To see the other types of publications on this topic, follow the link: Ni-based superalloy.
Dissertations / Theses on the topic 'Ni-based superalloy'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Ni-based superalloy.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Singh, Handa Sukhdeep. "Precipitation of Carbides in a Ni-based Superalloy." Thesis, Högskolan Väst, Avd för tillverkningsprocesser, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-6867.
Full textAbstract:
Alloy B is relatively new precipitation hardening superalloy. It´s applications are in the hot sections of the aero engines, rocket nozzles, gas turbines and in the chemical and petro-leum applications. The alloy is characterized by keeping high strength at elevated tempera-tures and high creep resistance. It´s excellent mechanical properties and corrosion resis-tance are due to the balanced amount of the coherent γ' matrix, combined with other alloy-ing elements and carbides. There are three types of carbides which can be found in nickel-based superalloys: MC, M 23C6 and M6C. Primary MC carbides act as source of carbon for the secondary carbides, which precipitate at the grain boundaries. They can have strengthening effect by hindering the movement of dislocations. In this work both simulation and experimental analysis are conducted in order to investi-gate the behaviour of the secondary carbides. JMatPro simulation is used to predict the behaviour of the material. Heat treatments are conducted at soak temperatures ranging from 920 °C to 1130 °C, with steps of 30 °C, and dwell times of 0.5, 1, 2 and 24 hours. Experimental methods included analysis at LOM, SEM, EDS, manual point counting and hardness tests. Main results show chromium rich M 23C6 carbides are stable at lower temperature compared to molybdenum rich M6C. Both appear as fine and discrete particles at the grain boundaries at 1070 °C. This morphology is believed to be beneficial for the mechanical properties of the alloy. The volume fraction varies between 0.6 and 1.3%. Hardness values are relevant in the range of 920-1010 °C. Above this range there is sudden drop of the hardness
2
Sathian, Sujith. "Metallurgical and mechanical properties of Ni-based superalloy friction welds." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0005/MQ46104.pdf.
Full text
3
Stewart, Calvin. "TERTIARY CREEP DAMAGE MODELING OF A TRANSVERSELY ISOTROPIC NI-BASED SUPERALLOY." Master's thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3606.
Full textAbstract:
Anisotropic tertiary creep damage formulations have become an increasingly important prediction technique for high temperature components due to drives in the gas turbine industry for increased combustion chamber exit pressures, temperature, and the use of anisotropic materials such as metal matrix composites and directionally-solidified (DS) Ni-base superalloys. Typically, isotropic creep damage formulations are implemented for simple cases involving a uniaxial state of stress; however, these formulations can be further developed for multiaxial states of stress where materials are found to exhibit induced anisotropy. In addition, anisotropic materials necessitate a fully-developed creep strain tensor. This thesis describes the development of a new anisotropic tertiary creep damage formulation implemented in a general-purpose finite element analysis (FEA) software. Creep deformation and rupture tests are conducted on L, T, and 45°-oriented specimen of subject alloy DS GTD-111. Using the Kachanov-Rabotnov isotropic creep damage formulation and the optimization software uSHARP, the damage constants associated with the creep tests are determined. The damage constants, secondary creep, and derived Hill Constants are applied directly into the improved formulation. Comparison between the isotropic and improved anisotropic creep damage formulations demonstrates modeling accuracy. An examination of the off-axis creep strain terms using the improved formulation is conducted. Integration of the isotropic creep damage formulation provides time to failure predictions which are compared with rupture tests. Integration of the improved anisotropic creep damage produces time to failure predictions at intermediate orientations and any state of stress. A parametric study examining various states of stress, and materials orientations is performed to verify the flexibility of the improved formulation.
A parametric exercise of the time to failure predictions for various levels of uniaxial stress is conducted.M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering MSME
4
Sun, Jifeng. "Time-dependent crack growth in a coarse-grained Ni-based superalloy RR1000." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4082/.
Full textAbstract:
The dwell fatigue crack growth behaviour of coarse grained RR1000 has been studied using advanced mechanical testing and characterization techniques. Crack growth under sustained loading has also been considered. Environmentally enhanced crack growth at high temperatures in air follows a stress assisted grain boundary oxidation (SAGBO) mechanism, with a 100-300 nm long Al2O3 intrusion ahead of the crack tip. When its thickness of reaches a critical value, this intrusion fails and crack advance ensues. The crack growth process is discontinuous and highly uneven. The dwell fatigue/sustained loading crack growth rates are affected by the stress relaxation ability of the materials, which is related to the size and distribution of tertiary γ' precipitates, testing temperature and stress state. Oxidation damage is deduced to be a dominant factor affecting crack growth over a range of temperature from 600 to 700 °C. At 700 °C oxidation damage begins to have an effect on fatigue crack growth at a dwell time of 30 s. Creep damage is suggested to make the dominant contribution to crack growth at 750 and 775 °C both in air and in vacuum.
5
Yang, Xiaoli. "Simulation of stray grain formation in single crystal Ni-based superalloy turbine blades." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424773.
Full text
6
Kountras, Apostolos 1970. "Metallographic study of gamma - gamma prime structure in the Ni-based superalloy GTD111." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/35753.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.Includes bibliographical references (leaf 73).
The potential for land-based turbine buckets material rejuvenation presents a significant commercial and scientific interest. Ni-based superalloy GTD111 is used at a number of GE-manufactured power generation turbines. The outstanding creep resistance features of Ni-based superalloys can be attributed to a large extent, to the gamma prime ([gamma]') precipitates found within the FCC [gamma]-matrix. Service-induced material degradation mainly involves coarsening and shape transformation of [gamma]'-phase precipitates; therefore, any bucket repair attempt should primarily address the restoration of [gamma]' precipitates to the original configuration. In the present study a quantitative metallographic analysis of GTD111 alloy under different conditions was performed. Several micrographs were taken and analysed using image analysis software. Gamma prime precipitate size was measured and compared between the different alloy conditions, leading to useful conclusions concerning material degradation as a result of high-temperature service exposure. In addition, microstructural transformations observed as a result of different heat treatments, formed the basis for investigation of procedures that can potentially restore the alloy microstructure in the original condition. High temperature solution and aging heat treatments sequence is considered as potentially sufficient for restoring the GTD111 microstructure. Finally, the measurements were examined for correlation with existing [gamma]' particle coarsening theory, by calculating and evaluating the metal service temperature during service. A satisfactory correlation exists.
by Apostolos Kountras.
S.M.
7
Edholm, Oscar. "Design of cemented carbide with Ni-based superalloy binder strengthened with y’-Ni3Al precipitates." Thesis, KTH, Materialvetenskap, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-261137.
Full textAbstract:
Replacement of cobalt in cemented carbides has gained in attention recently because threats of regulations due to health issues (cancerogenic effect), increased demand from the electric vehicle industry and the questionable extraction from countries like Democratic Republic of Congo. In this report the use of Ni-based binder as an alternative binder for cemented carbides has been explored. The design is based on producing a Ni-based superalloy binder which contains dispersed Ni3Al Gamma Prime (γ’) -phase precipitates in the binder matrix. The investigation focuses on the design of cemented carbide compositions and processes that ensures the formation of γ’- precipitates, the control of their morphology and distribution as well as the effect of heat treatment. To do this a Ni-Al master alloy has been designed that enables the formation of γ’-precipitates in WC-Ni-Al-X systems, produced by conventional powder metallurgy process including standard free sintering. Furthermore, the addition of usual elements in the cemented carbide industry (such as Ti, Cr, Ta, Nb) and their effect on the stability of γ’-precipitates has been investigated. A method to reveal the precipitates including ion-polishing and electro-etching has been developed. Basic mechanical properties such as hardness and toughness have been investigated, revealing particular crack propagation in Ni-based binder reinforced with γ’-precipitates. It was found that the common variables in cemented carbide manufacturing influence all aspects regarding the stability of γ’-phase. By varying the powder type, binder composition and content, the carbon balance, the WC grain size and the heating/cooling steps; the formation of γ’-precipitates (size, morphology, distribution, etc.) can be controlled to tailor the properties of the cemented carbide.Att hitta en ersättning av kobolt i hårdmetall har nyligen uppmärksammats bl.a. eftersom regleringar hotar användning av ämnet pga. dess cancerogenitet, en ökande efterfrågan från elfordonsindustrin samt den moraliskt tvivelaktiga utvinningen som sker i länder som Demokratiska Republiken Kongo. I denna rapport har användningen av ett nickel-baserat bindemedel som ett alternativt bindemedel för hårdmetaller undersökts. Designen är baserad på att producera en nickel-baserad superlegering som bindemedel som innehåller dispergerad Ni3Al Gamma Prim (γ’) – fas utfälld i bindemedlet. Utredningen fokuserar på designen av hårdmetallskompositioner och processer som försäkrar formationen av γ’-utfällningar, kontroller av dess morfologi, distributionen samt hur värmebehandlingar påverkar. För att kunna göra detta har en Ni-Al masterlegering skapats som möjliggör γ’-utfällningar i ett WC-Ni-Al-X system, producerat med konventionell pulvermetallurgiprocess inkluderat standard fri sintring. Dessutom har tillsatsen av vanliga ämnen i hårdmetallindustrin (such as TI, Cr, Ta, Nb) samt deras effekt på stabiliteten hos γ’-utfällningarna undersökts. En metod för att upptäcka utfällningarna, som inkluderar jonpolering och elektroetsning har utvecklats. Grundläggande mekaniska egenskaper som hårdhet och seghet har undersökts, vilket har avslöjat en speciell sprickutbredning i den nickelbaserade bindaren förstärkt med γ’-utfällningar. Det visade sig att de vanliga variablerna förenade med tillverkning av hårdmetall påverkar samtliga aspekter gällande stabiliteten hos γ’-utfällningar. Genom att variera pulvertyp, bindemedelkomposition och innehåll, kolbalansen, WC-kornstorlek och uppvärmning samt kylningssteg så påverkas bildningen av γ’-utfällningar (storlek, morfologi, distribution, etc..) som kan kontrolleras för att skräddarsy egenskaperna för hårdmetallen.
8
Phillips, Patrick J. "Advanced defect characterization via electron microscopy and its application to cyclically deformed Ni-based superalloy R104." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1330915484.
Full text
9
She, Dawei. "Analysis of Ni and Fe-based Alloys for Turbine Seal Ring Applications." Scholar Commons, 2018. http://scholarcommons.usf.edu/etd/7229.
Full textAbstract:
Metal sealing rings have been used widely in compressors, turbines and hydraulic devices. Such rings can extend out due to elasticity, and keep close contact with the valve wall, resulting in the formation of a functional seal under pressure. In this project, the failure of metal sealing rings is considered. Sealing component failure due to stress relaxation can threaten the safety of the whole steam turbine. The object of this study was to examine the stress relaxation response and corresponding changes in microstructure of metal sealing rings used in nuclear steam turbine under high temperature and applied stress. The two kinds of sealing ring samples were selected for GH4145 and GH2132.
In this paper, all samples were tested by accelerated simulation experiment. The test temperature was controlled at 400℃, 600℃, and 800℃. The 400℃ experiments lasted for 10, 20, 30 and 40 hours, while the 600℃ and 800℃ experiments lasted for 5, 10, 15 and 20 hours. The surface morphology was observed by metallographic analysis. It was found that the two kinds of sealing ring samples presented with a continuous development of grain coarsening and a decrease of the twins when time and test temperature were increased. The prolongation of time and increase of test temperature will drive the grain coarsening and reduce the twins faster. Many precipitates and inclusions were observed on the surface. The composition of precipitation was examined by scanning electron microscopy (SEM). It was further studied by testing samples with applied stress. The differences between the two tests and their influence on mechanical properties are discussed. The grain coarsening and twinning in the alloy will reduce the stress relaxation resistance of the material. Additionally, the precipitates and inclusions in the alloy may adversely affect the stress relaxation performance. Sealing rings using the nickel-based superalloys have stronger anti-stress relaxation performance than sealing rings made of iron-based superalloys.
10
Penso, Graciela Carolina. "Welding of X65 Internally Clad with Precipitation Strengthened Ni-Based SUperalloy Filler Metal: Application in Pre-Salt Oil Extraction." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480600980467914.
Full text
11
Foss, Benjamin. "Oxidation and oxygen transport in a commercial polycrystalline Ni-based superalloy under static and loading conditions." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/30732.
Full textAbstract:
The current demands of the aviation industry for increased gas-turbine efficiency pushes polycrystalline nickel-based superalloy turbine discs to their operational limits. This drive for improved efficiency necessitates higher turbine entry temperatures, requiring that alloys exhibit superior oxidation resistance. The synergistic effects of oxidation and high mechanical stresses pose a complex issue and can be responsible for a reduction in the fatigue life of these components. The principal aim of this thesis is to examine the oxidation behaviour and the associated transport mechanisms in the fine grain alloy RR1000 in the polished and shot-peened conditions, for classical and mechanically loaded conditions. To achieve this, experiments were conducted that integrated two-stage isotopic tracing, with 18O serving as a tracer element during the second stage oxidation, combined with focused-ion- beam secondary ion mass spectrometry (FIB-SIMS) and other complimentary techniques. Classical oxidation studies of FGRR1000 between 700-800°C characterised the oxidation behaviour in terms of the kinetics, microstructural changes and transport mechanisms. The alloy formed a mostly chromia external oxide, with discontinuous layers of rutile above and below the main oxide. Preferential grain boundary alumina internal oxidation, γ'-dissolution and recrystallisation occurred in the sub-surface below. The shot-peened alloy demonstrated expedited oxidation kinetics, attributable to short-circuit diffusion paths generation during peening and exposure. Combined isotopic oxidation/FIB-SIMS mapping revealed anionic/cationic growth in the external oxidation. Inward oxygen transport in the alloy, following diffusion through the semi-protective external oxide, took place preferentially along alloy/internal oxide interfaces. The FIB-SIMS maps were used to determine the oxygen tracer-diffusion coefficients in the external scale, which were also higher in the SP alloy. Thermodynamic modelling provided an insight into the γ'-dissolution and recrystallisation, which is not related to the cold work alone, and was subsequently described by oxidation- induced recrystallisation (OIR). A study of compressive and tensile loads on the oxidation behaviour used a purpose-built bending rig for use in an isotopic oxidation apparatus. Loading did not influence the oxidation products formed, but did bring-about expedited oxidation kinetics and changes to the oxide morphology. Arguably, the most significant effects took place in the sub-surface regions. Increased oxidation kinetics were attributed to the development of fast anion/cation diffusion paths as the alloy deformed by creep. Likewise, the creep-deformed microstructure is largely responsible for the morphological differences observed. A study of the residual stress relaxation in the shot-peened alloy due to thermal exposure and dwell-fatigue loading utilised X-ray residual stress analysis, electron back-scattered diffraction, micro-hardness testing and FIB microscopy. Thermal exposure at 700°C for 48 hours resulted in a large reduction in the residual stresses and work-hardening effects in the alloy, but the sub-surface remained in a beneficial compressive state. Oxidizing environments caused recrystallization in the near surface, but did not affect the residual stress-relaxation behaviour. Dwell-fatigue loading at the same temperature and total exposure times caused the residual stresses to return to approximately zero at nearly all depths. The roles of oxidation and oxygen transport during crack initiation and short crack growth of the shot-peened alloy were investigated. This used post mortem examination of specimens that had undergone dwell-fatigue loading at 700°C using isotopic tracing protocols. Preparation of crack cross-sections utilised a tangential FIB milling technique, which provided a suitable analysis region for different materials characterisation techniques. The relative distributions of the 16O-/18O- suggested that oxygen diffusion and the subsequent oxidation took place along grain boundaries, orientated in the direction of the maximum shear, immediately ahead of the crack. The growth of these oxide intrusions appears stress assisted; however, grain boundary primary-γ' precipitates may impede their continued growth. Complimentary Time-of-Flight SIMS (ToF- SIMS) and Energy Dispersive X-ray Spectroscopy (EDS) revealed the chemistry of the oxidation products. A possible mechanism for initiation and the initial crack growth under the current loading conditions was put forward.
12
Musinski, William D. "Modeling the effects of shot-peened residual stresses and inclusions on microstructure-sensitive fatigue of Ni-base superalloy components." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52337.
Full textAbstract:
The simulation and design of advanced materials for fatigue resistance requires an understanding of the response of their hierarchical microstructure attributes to imposed load, temperature, and environment over time. For Ni-base superalloy components used in aircraft jet turbine engines, different competing mechanisms (ex. surface vs. subsurface, crystallographic vs. inclusion crack formation, transgranular vs. intergranular propagation) are present depending on applied load, temperature, and environment. Typically, the life-limiting features causing failure in Ni-base superalloy components are near surface inclusions. Compressive surface residual stresses are often introduced in Ni-base superalloy components to help retard fatigue crack initiation and early growth at near surface inclusions and shift the fatigue crack initiation sites from surface to sub-surface locations, thereby increasing fatigue life. To model the effects of residual stresses, inclusions, and microstructure heterogeneity on fatigue crack driving force and fatigue scatter, a computational crystal plasticity framework is presented that imposes quasi-thermal eigenstrain to induce near surface residual stresses in polycrystalline Ni-base superalloy IN100 smooth specimens with and without nonmetallic inclusions. In addition, the effect of near surface inclusions in notched Ni-base superalloy components on MSC growth and fatigue life scatter was investigated in this work. A fatigue indicator parameter (FIP)-based microstructurally small crack (MSC) growth model incorporating crack tip/grain boundary effects was introduced and fit to experiments (in both laboratory air and vacuum) for the case of 1D crack growth and then computationally applied to 3D crack growth starting (1) from a focused ion beam (FIB) notch in a smooth specimen, (2) from a debonded inclusion located at different depths within notched components containing different notch root radii, and (3) from inclusions located at different depths relative to the surface in smooth specimens containing simulated shot peened induced residual stresses. Computational predictions in MSC growth rate scatter and distribution of fatigue life were in general accordance with experiments.
The general approach presented in this Dissertation can be used to advance integrated computational materials engineering (ICME) by predicting variation of fatigue resistance and minimum life as a function of heat treatment/microstructure and surface treatments for a given alloy system and providing support for design of materials for enhanced fatigue resistance. In addition, this framework can reduce the number of experiments required to support modification of material to enhance fatigue resistance, which can lead to accelerated insertion (from design conception to production parts) of new or improved materials for specific design applications. Elements of the framework being advanced in this research can be applied to any engineering alloy.
13
MARCHESE, GIULIO. "Study and characterisation of Ni-based superalloys produced by laser additive manufacturing." Doctoral thesis, Politecnico di Torino, 2017. http://hdl.handle.net/11583/2694925.
Full textAbstract:
The laser additive manufacturing techniques (LAM) are of growing interest in different industries due to their capacity to produce near net shape components in a single step. Particularly in the case of the Ni-based superalloys, LAM processes can produce highly complex shape components more cheaply with respect to the traditional technologies. However, nowadays, there is still a lack of knowledge on the study of the process parameters on the microstructure and densification levels and the study of tailored heat treatments to meet standard qualification as well as precise industrial requirements. This thesis presents the research performed on two Ni-based superalloys produced by LAM processes. Inconel 625 (IN625) fabricated by laser powder bed fusion (LPBF) and directed energy deposition (DED) and Hastelloy X (HX) built by LPBF. For LPBF IN625 alloy was studied the effect of different process parameters on the hardness and densification level, obtaining dense samples (relative density over 99.8 %). Afterward, it was studied in detail the microstructure, mechanical and thermomechanical properties of as-built IN625. The results showed that the tensile behaviours of as-built IN625 state are higher than minimum values requirements for wrought IN625 alloys, due to very fine dendritic structures (mainly less than 1.5 micron) coupled with high dislocation density. However, the characterisation of as-built IN625 samples revealed that heat treatments are necessary to decrease the residual stresses, reduce elements segregation, and produce mechanical properties suitable for industrial applications. For this reason, the microstructural evolution of LPBF IN625 under different heat treatments was investigated. According to the performed heat treatment, the mechanical properties of heat-treated IN625 were influenced by phases precipitation (mainly γʺ phases and carbides) and/or recrystallisation, grain growth and dissolution of dendritic structures. For DED IN625 alloy, the aim of this work was to determine the impact of different process parameters on the densification level (relative density over 99.7 %), hardness and microstructure in order to select the appropriate parameters for industrial production. Finally, LPBF HX alloy was studied in a research collaboration with GE AVIO s.r.l. The target of this work was to investigate the microstructure of as-built and post-processed LPBF HX alloy. The as-built HX samples showed different microcracks caused by the LPBF process, so some samples were hot isostatically pressed (HIPed) to close the microcracks. The microstructure, grain size, phases and hardness of the as-built, heat-treated and HIPed HX samples were investigated. The results revealed that in case microcracks appear during production, they can be removed after specific post processing, generating LPBF HX parts with grain size similar to standard solution heat-treated (SHT) wrought HX alloy.
14
Amaro, Robert L. "Thermomechanical fatigue crack formation in a single crystal Ni-base superalloy." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/37172.
Full textAbstract:
This research establishes a physics-based life determination model for the second generation single crystal superalloy PWA 1484 experiencing out-of-phase thermomechanical fatigue (TMF). The life model was developed as a result of a combination of critical mechanical tests, dominant damage characterization and utilization of well-established literature. The resulting life model improves life prediction over currently employed methods and provides for extrapolation into yet unutilized operating regimes. Particularly, the proposed deformation model accounts for the materials' coupled fatigue-environment-microstructure response to TMF loading. Because the proposed model is be based upon the underlying deformation physics, the model is robust enough to be easily modified for other single crystal superalloys having similar microstructure. Future use of this model for turbine life estimation calculations would be based upon the actual deformation experienced by the turbine blade, thereby enabling turbine maintenance scheduling based upon on a "retirement for a cause" life management scheme rather than the currently employed "safe-life" calculations. This advancement has the ability to greatly reduce maintenance costs to the turbine end-user since turbine blades would be removed from service for practical and justifiable reasons. Additionally this work will enable a rethinking of the warranty period, thereby decreasing warranty related replacements. Finally, this research provides a more thorough understanding of the deformation mechanisms present in loading situations that combine fatigue-environment-microstructure effects.
15
Kwong, Jacky King Chung. "On Understanding the Mechanisms Affecting Surface Integrity During Hole Making Operations on an Advanced NI-Based Superalloy." Thesis, University of Nottingham, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517845.
Full text
16
Storgärds, Erik. "High Temperature Fatigue Crack Growth in a Ni-based Superalloy : Modelling Including the Interaction of Dwell Times." Doctoral thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-121012.
Full textAbstract:
Safe life of gas turbines is always of major concern for manufacturers in order to ensure passenger safety and stable continuous power output. An increasing amount of resources have been put into research and development to assure that all safety aspects are covered in the design of new turbines and to ensure that enough frequent service intervals are scheduled to avoid complications. Many of these issues require good knowledge of material properties and of how to use these in the design process. Some of these relate to fatigue which is of major concern in all parts of a development programme. However, while some fatigue problems have been extensively studied, some have not. One example is crack growth with influence of dwell times at elevated temperature in combination with cyclic loading. Such loading conditions have been shown to give a different cracking behaviour compared to rapid cyclic loading, increasing the growth rate significantly with respect to the number of load cycles. Improved models for predicting this behaviour is therefore of major interest for gas turbine manufacturers, and could substantially increase the reliability. As a result, more research is needed in order solve these problems. The work presented in this dissertation has focused on how to predict life under the above-mentioned circumstances. The materials used in high temperature gas turbine applications are often nickel-based superalloys, and in this work the most common one, Inconel 718, has been studied. Mechanical experiments have been performed under operation like conditions in order to receive material data for the subsequent modelling work. The modelling approach was chosen such that the underlying physics of the dwell time cracking have been incorporated on a phenomenological basis, creating a model which can be physically motivated as well as used for industrial applications. The main feature of the modelling work has been to track material damage which is received from dwell times, how this interacts with cyclic loading and how it affects the crack growth rate, thus creating a load history dependent model. The outcome of this work has resulted in a model which is both easy to use and which has shown to give good correlation to available experimental data. Key components such as calibration for cheap and easy parameter determination, validation on complex engine spectra loadings, three dimensional crack growth, overload influences, material scatter, thermo-mechanical fatigue crack growth and the impact of high cycle fatigue loadings, are all covered in the presented work, both as experimental findings and as continuous development of the modelling concept. The dissertation consists of two parts. In the first an introduction with the theory and background to crack growth with dwell times is given, while the second part consists of 10 papers.
17
Dai, Huijuan. "A study of solidification structure evolution during investment casting of Ni-based superalloy for aero-engine turbine blades." Thesis, University of Leicester, 2009. http://hdl.handle.net/2381/4551.
Full textAbstract:
The need to achieve increased efficiency and performance in aerospace gas turbines requires advanced single crystal Ni-based superalloys to exhibit increased temperature capabilities. High temperature creep resistance of the turbine blades is one of the major limitations to meet increased performance goals of gas turbines. The ultimate creep resistance of the Ni-based superalloys is dependent on solidification structures formed during casting. In this study, multi-scale modelling method was used to study the solidification structure evolution occurring at various scales during investment casting. Modelling of solidification on the macroscopic scale of the process was implemented using a macroscopic Finite Element casting model, ProCAST, to predict thermal and flow profiles. The predicted thermal and flow data were then used as input in a meso-scale model Cellular Automaton Finite Element (CAFE) to predict grain structure and grain orientations during solidification. At the micro-level, detailed dendritic morphology and solutal interaction were investigated using a μMatIC model. Using the multi-scale approach, grain selection in spiral grain selector, formation of new grains ahead of solidification interface and the effect of dendrite packing patterns on primary dendrite spacing were investigated. The effect of spiral shape on grain selection in single crystal grain selector has been systematically studied. It was found that the efficiency of the spiral selector significantly depends on its geometry and dimensions. The spiral becomes more efficient with a smaller wax wire diameter, larger spiral diameter and smaller take-off angle. Formation of new grains ahead of solid/liquid growth front was simulated. Stray grain formation in the platform region of turbine blades was investigated, indicating that the alloy with greater susceptibility to the formation of stray grains has lower critical nucleation undercooling. The columnar-to-equiaxed transition (CET) during solidification was predicted and the effect of material properties on the CET was analyzed. The analysis results revealed that the CET can be promoted by: (1) decreasing the critical nucleation undercooling; (2) increasing the nuclei density of the melt; and (3) extending the solidification range. Dendrites with different packing patterns were used to simulate dendrite spacing adjustment during solidification. It was found that the branching of secondary and tertiary arms in the hexahedral packing is easier than that in the cuboidal packing, leading to a smaller average spacing.
18
Lemos, Georges [Verfasser], Florian [Gutachter] Pyczak, and Ulrich [Gutachter] Tetzlaff. "Development of Ni-based superalloy metal matrix composites, featuring high creep resistance / Georges Lemos ; Gutachter: Florian Pyczak, Ulrich Tetzlaff." Cottbus : BTU Cottbus - Senftenberg, 2021. http://d-nb.info/1227930690/34.
Full text
19
Jiang, Rong. "Study of fatigue crack initiation and propagation mechanisms in an advanced Ni-based superalloy : effects of microstructures and oxidation." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/386208/.
Full textAbstract:
Low Solvus, High Refractory (LSHR) alloy is a latest generation of turbine disc alloy which contains relatively high Co and Cr levels compared with incumbent alloys, this provides a low solvus temperature for enhanced high temperature processing versatility, and the alloy is designed to operate at higher temperatures to achieve higher thrust-to-weight ratio and higher fuel efficiency. Understanding the fatigue performance of the LSHR alloy along with the coupled influences of deformation and oxidation damage is important for both its practical application and in further development of turbine disc alloys. Short crack tests have been conducted on coarse grained (CG) and fine grained (FG) LSHR alloys by uninterrupted and interrupted three-point bending with a replication procedure at room temperature, 650 and 725 oC in air and vacuum under a sine waveform (20Hz) and/or 1-1-1-1 trapezoidal waveform to investigate fatigue crack initiation and early propagation. The results show that fatigue lives in the LSHR alloy are shortened by high temperature, high oxygen partial pressure and low frequency loading waveforms which are associated with more intergranular fracture mechanisms. At room temperature, where the effect of oxidation is absent, twin boundary (TB) cracking in relatively large grains dominates the crack initiation process along with occasional crack initiation due to slip band cracking. Activation of the primary slip systems parallel to the TB at matrix and twin and high resolved shear stress associated with high Schmid factor (SF) are required for TB crack initiation. Cracks preferentially propagate along slip bands associated with high SF slip systems after initiation. But cracks also propagate along slip bands associated with slip systems with lower SF if the inclination angle between the slip band ahead of the crack tip and the crack segment of the crack tip is small enough to enable a steady transition (or non-deflected growth) of cracks across the grain boundary (GB). At elevated temperatures (i.e. 650 and 725 oC), fatigue crack initiation and early short crack propagation behaviour are closely related to coupled deformation-oxidation damages. Plentiful crack initiation mainly occurs at GBs and/or γ/γʹ interfaces (in the FG variant) with bulged Ni/Co-rich oxides and Cr/Ti/Al oxide intrusion due to oxide cracking. Cracks subsequently propagate along oxidised GBs at the surface and exhibit significant crack coalescence in the final stages of fatigue life. In terms of crack propagation in the depth direction, this is a consequence of the competing effects between mechanically-driven and oxidation-assisted crack propagation, and exhibits transgranular or intergranular or mixed inter-transgranular propagation. Formation of bulged Ni/Co-rich oxides and Cr/Ti/Al oxide intrusion along grain boundaries is accompanied by dissolution of γʹ precipitates, and is closely related to the strain localisation which is associated with grain orientation and applied stress. The boundaries of high/low SF grains are preferential sites for bulged Ni/Co-rich oxides and Cr/Ti/Al oxide intrusion formation. Strain-assisted formation of internal GB Cr/Ti/Al oxide intrusion can facilitate coupled formation of GB bulged Ni/Co-rich oxides by providing abundant Ni and Co. Apart from the significant oxidation at grain boundaries and γ/γʹ interfaces, uniform surface oxide scale along with internal Al oxide particles form within grains and primary γʹ. Studies of long fatigue crack growth (FCG) behaviour in LSHR alloy at 650 and 725 oC in air and vacuum under trapezoidal waveforms of 1-1-1-1 and 1-20-1-1 indicate that a CG structure possesses better FCG resistance due to the enhanced slip reversibility promoted by planar slip as well as the reduction in grain boundary area. The fatigue performance of the LSHR alloy is significantly degraded by the synergistic oxidation effect brought about by high temperature, high oxygen partial pressure and dwell at the peak load, associated with increasingly intergranular fracture features and secondary grain boundary cracking. Secondary cracks are observed to be blocked or deflected around primary γʹ, carbides and borides, and their occurrence closely relates to the roughness of the fracture surface, FCG rate and grain boundary oxidation. The apparent activation energy analysis provides a further insight into the underlying mechanism of the FCG under dwell-fatigue testing conditions, and confirms that oxidation fatigue is the dominant process contributing to the intergranular failure process. At high enough crack growth rates and at lower temperatures, mechanically-driven fatigue crack growth processes can outstrip crack-tip oxidation processes.
20
Utada, Satoshi. "Effect of a Prior Plastic Deformation during Heat Treatments on the Mechanical Properties of Ni-Based Superalloys for Turbine Blade Application Evolution of superalloy for turbine airfoil and development of recycling technology Platinum containing new generation nickel-based superalloy for single crystalline application Tensile, low cycle fatigue and very high cycle fatigue characterizations of advanced single crystal nickel-based superalloys Creep Property and Phase Stability of Sulfur-Doped Ni-Base Single-Crystal Superalloys and Effectiveness of CaO Desulfurization Evaluation and comparison of damage accumulation mechanisms during non-isothermal creep of cast Ni-based superalloys." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0019.
Full textAbstract:
Les superalliages monocristallins base Ni sont utilisés pour la conception des aubes de turbines en raison de leur excellente durabilité à haute température. Lors de la production d'une aube de turbine, une déformation plastique (DP)inattendue peut être introduite dans le matériau. Dans cette étude, les matériaux monocristallins ont été pré-déformés entre les traitements thermiques de mise en solution et de revenu pour simuler la DP pouvant être rencontrée lors des étapes de production. Des tests mécaniques sur les matériaux pré-déformés ont été effectués pour comprendre l'effet de cette DP.Au cours des traitements thermiques de revenu du superalliage monocristallin AM1 pré-déformé, un grossissement des précipités γ′ plus rapide et une nucléation accélérée de pores ont été observés à proximité des bandes de glissement introduites lors de la DP à température ambiante. Au cours de la déformation par fluage de l’AM1 pré-déformé dans des conditions de haute température/basse contrainte (≥ 950 °C), les bandes à microstructure grossière sont des sites préférentiels d’accumulation du dommage de fluage induit par diffusion, induisant de la recristallisation et une réduction drastique des propriétés de fluage. Dans des conditions de basse température/haute contrainte (≤ 850 °C), le cisaillement de la microstructure est facilité dans les bandes à microstructure grossière et il réduit également les propriétés de fluage.La recristallisation n'est pas été observée dans des ces conditions de fluage à basse température car les mécanismes diffusifs sont ralentis. Ces résultats ont été confirmés via des essais de fluage sur des matériaux pré-déformés suivant différent chemin de pré-déformation (température, position de la DP dans le cycle thermique…). Le superalliage monocristallin CMSX-4 Plus a été testé de manière similaire à l'AM1 pour comprendre l'effet de la composition chimique. L'effet de la DP sur la microstructure de l'alliage est plus limité pour cet alliage par rapport à celui sur l’AM1. Par conséquent, la pré-déformation n'a pas montré de chute de la durée de vie pour le CMSX-4 Plus à des températures inférieures à 1050 °C. Par contre, pendant le fluage de CMSX-4 Plus à 1150 °C, la pré-déformation a montré un impact spectaculaire sur la durée de vie et la ductilité via les mêmes mécanismes que ceux observés pourl’AM1 à 1050 °C.Afin de régénérer les propriétés des superalliages monocristallins pré-déformés, un traitement thermique de restauration a été ajouté après la DP. Le traitement de restauration a permis de restaurer la microstructure après la DP à température ambiante avec succès, et les propriétés de fluage des matériaux restaurés sont équivalentes à celles de l'AM1 et duCMSX-4 Plus vierges de pré-déformationNi-based single crystal (SX) superalloys are used for turbine blade applications because of their high-temperature durability. During the production of a turbine blade, unexpected plastic deformation (PD) can be introduced to the material. In this study, SX materials were pre-deformed in between solution and aging heat treatments to mimic PD during production. Mechanical tests on the pre-deformed materials have been performed to understand the effect of the prior PD.During aging treatments of pre-deformed AM1 SX superalloy, faster coarsening of γ′ precipitates and enhanced void nucleation were observed in the vicinity of slip bands which were introduced by PD at room-temperature. During creep deformation of pre-deformed AM1 at high temperature/low stress conditions (≥ 950 °C), the microstructure coarsened bands act as diffusion induced creep damage accumulating paths, further triggering recrystallization and resulting in drastic reduction of creep properties. At low temperature/high stress conditions (≤ 850 °C), microstructure shearing was facilitated in the microstructure coarsened band and it decreased creep properties. Recrystallization was not observed at lower temperature creep because the diffusion damage was suppressed. These relationships have been explained by creep tests on pre-deformed materials prepared by different pre-deformation temperatures and heat treatment procedures.CMSX-4 Plus SX superalloy was tested similarly to AM1 to understand the effect of the chemical composition. Effect of pre-deformation on alloy’s microstructure was mild in CMSX-4 Plus compared to that in AM1. Therefore, the predeformation did no exhibit large creep life debit in CMSX-4 Plus at temperatures lower than 1050 °C. However, during creep of CMSX-4 Plus at 1150 °C, pre-deformation presented huge impact on creep life and ductility by the same mechanisms as the ones observed for AM1 at 1050 °C.In order to restore properties of pre-deformed SX superalloys, rejuvenation heat treatment was added after PD.Rejuvenation treatment successfully restored microstructure after PD at room-temperature, and creep properties of rejuvenated specimens were shown to be equivalent to that of original AM1 and CMSX-4 Plus without PD
21
Chen, Yiqiang. "High-resolution microstructural and microanalysis studies to better understand the thermodynamics and diffusion kinetics in an advanced Ni-based superalloy RR1000." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/highresolution-microstructural-and-microanalysis-studies-to-better-understand-the-thermodynamics-and-diffusion-kinetics-in-an-advanced-nibased-superalloy-rr1000(1d4e96e0-b362-484e-82cb-bec18cab850b).html.
Full textAbstract:
The commercial polycrystalline superalloy RR1000 developed for turbine disc applications contains a large number of alloying elements. This complex alloy chemistry is required in order to produce appropriate microstructures and the required mechanical properties, such that the most important strengthener γʹ displays complex alloy chemistry. The broad aim of this project is to develop an approach to measuring the composition of γʹ precipitates at a broad range of length scales from nanometres to hundreds of nanometres, and subsequently develop a better understanding of the role of thermodynamics and diffusion kinetics on γʹ phase separation and precipitate growth. A solution of the absorption-corrected EDX spectroscopy to spherical particles was developed in our work, therefore enabling the quantitative analysis of precipitates' composition using an absorption-corrected Cliff-Lorimer approach. By performing this quantification, size-dependent precipitate compositional variations were obtained. Examination of this quantitative approach was compared to thermodynamic calculations of primary γ' precipitates possessing equilibrium compositions. Given the development of semi-quantitative compositional measurements for spherical γʹ precipitates and that cooling is one of the most common and critical regimes in physical metallurgy of Ni-based superalloys, this approach was then applied to study the local compositional variations that are induced in γ' precipitates when the alloy RR1000 undergoes different cooling rates. These measured compositions have been compared to detailed thermodynamic calculations and provide new experimental evidence of the importance of the dominant role of aluminium antisite diffusion in determining the low-temperature growth kinetics of fine-scale γ' precipitates. We have applied a similar analysis approach to study the compositional variations of γʹ cores within the class of secondary precipitates upon cyclic coarsening and reversal coarsening. It was shown that supersaturated Co in secondary γʹ exhibits an overall trend towards the equilibrium but Co content can significantly increase as γʹ coarsens. It was demonstrated that the limited elemental diffusivity in γ and γʹ compared to the observed coarsening rate in the coarsening regime results in the long-lasting Co supersaturation in γʹ and builds up elemental enhancements or depletions. These inhomogeneous elemental distributions produce compressive elastic constraints on large-scale secondary γʹ, therefore inducing morphological instability of these γʹ and causing the reversal coarsening. These results enable us to better understand the role that both thermodynamics and limited diffusion kinetics plays in controlling the complex microstructures of γ' precipitates.
22
Cruchley, Sam. "The oxidation damage of Ni-based superalloy, RR1000, with different surface modifications and the role of oxidation in fatigue crack initiation." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5894/.
Full textAbstract:
The oxidation behaviour of RR1000 with different surface modifications has been well studied using detailed metallographic and mass gain measurements. The oxide comprises of an external chromia scale with isolated grains of TiO\(_2\) on the outer surface. Sub-surface internal alumina is present, beneath which the presence of TiN occurs (at higher temperatures >800\(^o\)C), all contained within a ɣ' denuded zone. The chromia external scale growth rate is significantly greater than pure chromia on chromium and the enhancement is attributed to the increased ionic transport caused by doping of the chromia layer with Ti. This effect is still seen regardless of surface condition prior to oxidation. Oxides, especially internal intergranular oxides have been shown to crack under room temperature fatigue conditions, causing a significant fatigue life deficit at a maximum applied stress of 800 MPa and 1000 MPa. At 825 MPa, it is suggested that plastic yielding of the ɣ' denuded zone initiated leading to a substantial increase in fatigue life, through either blunting the crack by deforming to accommodate the stress concentration at the crack tip or by preventing cracking of the oxides.
23
Seret, Anthony. "Influence de la mise en forme sur les cinétiques de précipitation durcissante dans les superalliages base nickel Inconel® 625 et AD730™." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEM030.
Full textAbstract:
Les superalliages base nickel possèdent d'exceptionelles propriétés mécaniques et de résistance à la corrosion à haute température. Ces propriétés mécaniques proviennent en partie de la précipitation durcissante des phases Ni3Nb γ″ ou Ni3(Al, Ti) γ′. L'objectif de cette thèse est de mieux comprendre comment les opérations de mise en forme de pièces industrielles peuvent influencer cette précipitation. Deux superalliages ont été étudiés dans cette thèse : Inconel® 625 mis en forme par déformation à température ambiante et renforcé par la phase γ″, et AD730™ mis en forme par forgeage à chaud et renforcé par la phase γ′. Des traitements thermiques, essais mécaniques et thermomécaniques ont été réalisés afin d'une part de reproduire les niveaux de déformation plastique et/ou la structure de grains obtenus à la fin d'étapes de mise en forme industrielle, et d'autre part de déclencher la précipitation ou d'induire l'évolution des précipités existants. Les microstructures ont ensuite été caractérisées quantitativement par microscopie à balayage au regard de la structure de grains, l'organisation des dislocations et d'état de précipitation. Dans l'alliage Inconel® 625, la précipitation γ″ lors d'un traitement thermique à 650 °C n'est pas influencée par une déformation préalable appliquée, validant la pertinence de la température de 650 °C pour procurer un durcissement homogène aux pièces industrielles. Dans l'alliage AD730™, la germination de précipités γ′ lors d'un refroidissement après compression à chaud a lieu plus tôt dans les grains non recristallisés que dans les grains recristallisés, par relaxationélastique à la germination. De manière concomitante, le front de recristallisation dissous ces précipités γ/γ′ présents dans les grains non recristallisés pour éviter toute interface γ/γ′ incohérente. Des précipités γ′ reprécipitent ensuite dans le front de recristallisation avec une interface γ/γ′ cohérente dans les grains recristallisés, et peuvent par la suite se subdiviser pour diminuer l'énergie élastique globale. Cette thèse comprend le développement d’outils spécifiques : réduction du bruit de mesure de cartographies EBSD pour une estimation plus précise des densités de dislocations géométriquement nécessaires, analyse d’image et modèle de précipitationNickel-based superalloys possess exceptional mechanical properties and corrosion resistance at high temperature. These mechanical properties result partly from the hardening precipitation of Ni3Nb γ″ or Ni3(Al, Ti) γ′ phases. The objective of this PhD is to better understand how forming operations of industrial parts may influence this precipitation. Two superalloys have been studied in this PhD : Inconel® 625 alloy formed a room temperature and reinforced by the γ″ phase, and AD730™ alloy hot forged and reinforced by the γ′ phase. Thermal treatments, mechanical and thermomechanical tests have been performedin order to, on the one hand, reproduce the plastic strain levels and/or the grain structure obtained at the end of industrial forming operations, and on the other hand to trigger the precipitation or the evolution of already existing precipitates. The microstructures have then been quantitatively characterizedby scanning electron microscopy regarding the grains structure, the dislocationsorganization and the precipitation state.In the Inconel® 625 alloy, the nucleation of γ″ precipitates during a thermal treatment at 650 °C is not influenced by a strain applied before, supporting the relevancy of the 650 °C temperature to bring an homogeneous hardening to industrial parts. In the AD730™ alloy, the γ′ precipitation during a cooling after a hot compression takes place sooner in unrecrystallized grains than in recrystallized grains, by elastic relaxation when nucleating. Concomitantly, the recrystallization front dissolves these γ′ precipitates present in unrecrystallized grains to avoid any incoherent γ/γ′ interface. Then γ′ precipitates reprecipitate on the recrystallization front with a coherent γ/γ′ interface in recrystallized grains, and can afterwards subdivide to reduce the global elastic energy. This PhD includes the development of specific tools : reduction of the measurement noise of EBSD maps for a more accurate assessmentof geometrically necessary dislocations densities, image analysis and precipitation model
24
Underhill, Richard P. "The spray forming of Ni based superalloys." Thesis, University of Oxford, 1995. http://ora.ox.ac.uk/objects/uuid:a26505d4-90cf-41ff-86e9-fbf903c9a87f.
Full textAbstract:
The main aim has been to investigate the effect of process parameters on the spray forming of UDIMET 720 and in particular to understand the mechanism of grain size evolution in the deposit using a combination of experimental and computer modelling techniques. Samples of two spray formed Ni superalloys, MAR-M-002 and UDIMET 720, have been re-heated into the solid/liquid region and the fully solid region just below the solidus temperature for a series of times to try and reproduce the situation of grain growth in a spray formed deposit. Grain growth in the solid/liquid region follows the equation: d3=d03 +Kt, where d is the grain size, d0 is the initial grain size, K is the coarsening rate constant and t is the time. Coarsening rate constants have been determined for temperatures in the solid/liquid region and they increase with increasing temperature/decreasing solid fraction. Existing spray forming equipment for Al alloys has been modified to manufacture UDIMET 720 deposits. Process conditions were monitored continually during spray forming, in particular the temperature of the deposit by embedded thermocouples and infra red thermal imaging of the deposit top surface. Above a deposit temperature of ≈1250°C the microstructure consists of equiaxed fine grains (20μm-35μm) and the porosity is low (<1%). Below this deposit temperature the microstructure consists of droplet "splats" and the porosity is higher (2-4%). The measure grain size increases with increasing deposit temperature and solidification time and agrees reasonably well with the predicted grain size using the above equation. A commercial finite difference based fluid dynamics software program, FLUENT, has been used to model the 2-dimensional dynamic and thermal behaviour of UDIMET 720 droplets during gas atomisation and spray forming. The effect of atomising gas pressure, spray distance and melt mass flow rate on the equilibrated droplet spray temperature has been examined and shows similar variations with process parameters as the measured maximum deposit temperature. The predicted spray temperature at the substrate is always higher than the measured maximum deposit temperatures under all conditions, and increases with (i) decreasing gas pressure, (ii) decreasing spray distance and (iii) increasing MFR. Mean droplet temperatures and velocities are strongly dependent on droplet size, the mean droplet temperature decreases and mean droplet axial velocities increases with decreasing droplet size.
25
Yablinsky, Clarissa A. "Characterization of Fatigue Mechanisms in Ni-based Superalloys." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1285006918.
Full text
26
Pace, Michael. "Oxidation of MCrAlY coatings on Ni-based superalloys." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/6670.
Full textAbstract:
Ensuring a sustainable power generation supply into the future is of worldwide importance. A combination of power generation methods to meet this (including both fossil plant and renewables) is a certainty. Therefore, the maintenance of conventional fossil-fired plants is required to provide a low cost, flexible and reliable electricity supply, and in order to conserve fuel resources it is important to ensure they operate as efficiently as possible. Lifetime predictions of important components (such as turbine blades in industrial gas turbine engines) are essential in order to avoid failures and unnecessary downtime, improve the ability to schedule routine maintenance work and to help develop new coating systems to meet the ever more demanding requirements. Better models would allow improved predictions and mean that service schedules could be set with better accuracy thereby, limiting downtime and reducing costs as well as being better able to predict coating performance and thus increase engine efficiency. Ni-based superalloys are a common material utilised for turbine blades due to their high temperature strength. Coupled with MCrAlY coating systems and thermal barrier coatings (TBC) they are able to withstand both the high temperatures and arduous environments they will encounter during service. In order to effectively predict the lifetime of components such as turbine blades it is vital to understand the oxidation behaviour of these systems and how factors such as the MCrAlY composition, processing factors and thermal cycling affect their performance. MCrAlY coatings are commonly utilised to protect the alloy substrate from the high risk of oxidation and corrosion. The M in MCrAlY is generally Ni, or Co or a combination of the both. These systems work by elements within the MCrAlY (notably Al) reacting with oxygen in the environment and forming protective thermally grown oxides (TGO). As these systems are very complex, a detailed understanding is needed of all areas, especially the TGO. This research was concerned with the characterisation of the TGOs formed on different compositions of MCrAlY coatings as a function of time and temperature. A range of coated samples were exposed to both isothermal and cyclic conditions to simulate service conditions. A wide range of analytical techniques have been utilised including scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDS), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and dual beam focussed ion beam field emission gun scanning electron microscope (FIBSEM) for phase characterisation. Detailed analyses of the MCrAlY bond coat, TGO and TBC layers have been made with regards to how composition, temperature, processing parameters and thermal cycling affect them. Thermodynamic equilibrium calculations have also been performed using commercial software in conjunction with a thermodynamic database for Ni-based superalloys to provide information about phase stabilities at equilibrium. Four MCrAlY coating systems have been analysed in detail in this research (NiCoCrAlY, NiCrAlY, CoCrAlY and CoNiCrAlY). Thermodynamic equilibrium calculations predicting phase amounts and compositions have been compared with experimental data with good correlation. The microstructural evolution from short term to long term ageing has been charted for all bond coat systems. The Co containing systems were shown to be very similar showing a main aluminium rich TGO, with precipitates forming in the TGO multi-oxide/spinel regions above it. The NiCrAlY was shown to have a completely different behaviour, forming a mixed Cr/Al oxide initially followed by an aluminium rich TGO. Whilst precipitates were seen in the aluminium TGO, no multi-oxide/spinel regions were seen. Further in depth analysis of the oxide formations was undertaken. The oxide on all coating systems was shown to form via similar mechanisms, whereby the Y in the bond coat is doping the oxide and changing the growth mechanism. Analysis of the TGO showed that on the Co containing coatings the TGO was alumina and on the NiCrAlY a mixture of chromia, mixed Al/Cr oxide and alumina beneath. The form Y has taken in the bond coat was quantified using high resolution techniques, as were the Y precipitates within the TGO. Each bond coat system was seen to contain different forms of precipitate however they were all thought to mainly form via the outward diffusion of Y from the bond coat, although it is possible some were existing particles in the bond coat enveloped by the growing oxide. It was also discovered that in the NiCoCrAlY system Ti precipitates were present along with strong Ti segregation at the boundaries, where Ti was thought to have diffused from the superalloy substrate to the oxide. The presence of Ti is thought likely to alter the grain boundary diffusion and probably increase scale growth. The multi-oxide/spinel regions (shown to be mixed Co, Cr, Al, Ni oxides) were shown to correlate well with similar formations noted in previous literature and are thought to be a result of the variable interface morphology of the coatings resulting in localised Al depletion and the formation of breakaway oxides. The effect that processing parameters and thermal cycling can have on the system has also been investigated. It was shown that the interface morphology (which is linked closely to the processing parameters) can greatly affect the oxide formation, both in terms of precipitates within the TGO and multi-oxide/spinel regions. The interface morphology was also shown to have important implications with regard to the cyclic life, through its effect on the stresses within the system, which in turn can affect the cyclic life. The nature of the oxide formations were also shown to influence the cyclic life.
27
Ogden, Sarah L. "Microstructural evolution in coated single crystal Ni-based superalloys." Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/12824.
Full textAbstract:
Ni-based superalloys are primarily used in the manufacturing of critical gas turbine components, such as rotating blades. The drive for increased efficiency has led to a continuous rise in engine operating temperatures, and therefore these components are exposed to conditions that can ultimately compromise their mechanical integrity and therefore limit their service life. There is a desire to extend the component's life and also to avoid any premature failures, and therefore understanding of the material's stability and properties throughout component life is increasingly important. The identification of features in the microstructure of Ni-based superalloys which change systematically with time and temperature may allow it to be used as a 'time-temperature' recorder. This could enable a determination of the effective temperature a component will have experienced, and in conjunction with known values of operating stress, an estimate of the remaining service life can be made.
28
Newman, Scott. "Microstructural evolution in coated conventionally cast Ni-based superalloys." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12468.
Full textAbstract:
The aim of this research project was to investigate the microstructural changes of MCrAlY coated Ni-based superalloys that are routinely used in industrial gas turbine engines for power generation. One of the main aims of the characterisation was to understand ageing time and temperature effects on the microstructural evolution so that a methodology could be developed where the characterisation of a thermally exposed microstructure can be used to estimate unknown service exposure conditions.
29
Di, Martino Irene. "Microstructure modelling of coated single-crystal Ni-based superalloys." Thesis, Loughborough University, 2004. https://dspace.lboro.ac.uk/2134/35527.
Full textAbstract:
Market-driven requirements for better performance of gas-turbine engines are the main drive towards the development of more advanced Ni-based superalloy/coating systems. The durability of such coated components is a crucial issue faced by the power generation and the aircraft industries, because coating life mainly controls the refurbishment and replacement of many engine parts, such as blades. Coated systems undergo a number of microstructural changes as a result of thermal exposure, which need to be understood for the creation of accurate microstructure-based life-prediction models. This work was mainly concerned with the evolution of the microstructure in both the parent material and the coating as a function of temperature and time in a number of single-crystal Ni-based superalloys, coated with an MCrAlY coating. The microstructural changes occurring at various time/temperature conditions were studied using thermodynamic equilibrium calculations, scanning electron microscopy and energy dispersive X-ray analysis.
30
Sjöström, Julia, and Helena Åkesson. "Investigation of Ductility Dip at 1000˚C in Alloy 617." Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209823.
Full textAbstract:
Alloy 617 displays a ductility dip during straining at exactly 1000˚C, leading to brittle fracture. A sudden decrease in ductility appearing during Gleeble hot ductility tests of Ni-based superalloys is a well-known phenomenon, while its cause is unknown. Many mechanisms have been established as possible contributors to the issue, and in later years not one, but the simultaneous presence of several of these mechanisms were confirmed as the cause. The ductility dip leads to solid state cracking and a specific solid state cracking phenomenon known as ductility dip cracking is specifically common in Ni-based superalloys. Ductility dip cracking is identified by intergranular cracks and the occurrence of specific precipitates, among other things. This work investigates the possibility that the decreased ductility is due to ductility dip cracking. Furthermore, other possible explanations are investigated. Visual examination was conducted through LOM, SEM and chemical analysis using EDS technique. Combined with thermodynamic calculations, the existence of Cr-rich M23C6 carbides, Ti(N,C) and Mo-rich particles, most likely M3B2, were confirmed. Further, it is established that the ductility dip is related to the lack of dynamic recrystallization at 1000˚C. It is not confirmed that the ductility dip in alloy 617 is due to ductility dip cracking.Nickelbaslegeringen 617 uppvisar en minskning i duktilitet under Gleeble-dragprovning vid exakt 1000˚C vilket leder till sprött brott. En plötslig sänkning av duktiliteten vid varmdragning av Ni-baserade superlegeringar är ett välkänt fenomen, dock är orsaken inte fastställd. Många mekanismer har bekräftats som bidrag till problemet och under de senaste åren har den simultana närvaron av fler av dessa mekanismer bekräftats som orsaken. Sänkningen i duktilitet leder till sprickbildning i fast fas och en specifik typ av sprickbildning känd som ”ductility dip cracking” är speciellt förekommande i Ni-bas legeringar. Denna identifieras bland annat genom intergranulära sprickor och närvaron av specifika utskiljningar. Detta arbete undersöker möjligheten att duktilitetssänkningen beror på ”ductility dip cracking”. Dessutom undersöks fler tänkbara förklaringar. Visuell granskning genomfördes via LOM och SEM och analys av sammansättningar via EDS-analys. I kombination med termodynamiska simuleringar blev förekomsten av Cr-rika M23C6 karbider, Ti(N,C) och Mo-rika partiklar, troligtvis M3B2, bekräftad. Fortsatt är det bekräftat att duktilitetssänkningen är relaterat till avsaknaden av rekristallisation vid 1000˚C. Det är inte bekräftat i detta arbete att duktilitetssänkningen i legering 617 beror av ”ductility dip cracking”.
31
Smith, Timothy M. Jr. "Orientation and Alloying Effects on Creep Strength in Ni-Based Superalloys." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480599553519057.
Full text
32
Ye, Ruoru. "Microstructure characterisation and mechanical behaviour of linear friction welded Ni-based superalloys." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/6405/.
Full textAbstract:
Linear friction welding (LFW) has been selected as a screening method to investigate the solid state joining of the Ni-based superalloys: IN718, RR1000, Alloy10, IN100, IN713LC and CMSX4, with the volume fraction (Vf) of γʹ range from 20-70%. Similar welds of each alloy and one dissimilar weld, IN718-IN713, are studied in this project. The extreme thermomechanical history during LFW results in dynamic recrystallisation in the weld zone, dissolution and reprecipitation of the strengthening phase in the HAZ. Sustained load crack growth (SLCG) threshold testing was carried out at 650°C in air for all the similar welds. Weld IN718 which had a low Vf of γʹ+γʹʹ, had the highest threshold (25MPa√m) and highest SLCG resistance. However, there was no such clear effect of γʹ size and volume fraction on threshold value (9-19MPa√m) in welds with a high γʹ content. The crack growth rates of all these welds accelerated sharply from 10-5 to 10-2mm/s over a limited increase in K. A comprehensive mechanical assessment of dissimilar weld IN718-IN713 was carried out, including tensile tests at room temperature and 630ºC, low-cycle and high-cycle fatigue tests at 630ºC on notched specimens, fatigue crack propagation testing at 630ºC, and stress rupture testing at 650ºC.
33
He, Shuang. "Interactions and phase stability in Ni-rich binary alloys." Licentiate thesis, KTH, Materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-189865.
Full textAbstract:
Ni-based superalloys are the important materials for gas turbines in advancedaeroplane engines . The addition of refractory elements to these superalloys,such as rhenium and tungsten, can significantly improve the hightemperatureperformance by so-called solid-solution hardening. Although thestrengthening effect of refractory elements in Ni-based superalloys have beenknown for a long time, the effective interactions among alloying componentsas well as the atomic ordering in the alloy systems are still under investigationand even under debate. In this work, we study these interactions and thisordering for two binary alloys, Ni-rich Ni-Re and Ni-rich Ni-W, by means ofab initio simulations and statistical mechanics simulations based on the IsingHamiltonian. For the Ni-rich Ni-Re alloys, we show that the effective cluster interactionsvary substantially depending on the temperature, concentration of the componentsand the magnetic state of the matrix. The strain-induced interactionshave large contribution to the nearest-neighbor pair-interactions and some multisitecluster-interactions in the ferromagnetic and nonmagnetic states. Theordering tendency of binary Ni-Re alloy systems can be predicted in terms ofordering energy and enthalpy of formation. We show that the D1a orderedstructure should be stable at the concentration of 20 at.% Re in the Ni-rich Ni–Re alloy system. The Monte Carlo simulations of Ni-Re random alloysshow the existence with the D1a-Ni4Re ordered structure at low temperatures. We also calculated lattice parameters for different compositions of Ni-rich Ni-W alloys, and we find that lattice parameters of random Ni-W alloys increaselinearly with the concentration of W. This is in good agreement withthe Vegard’s law predictions and experimental data. We investigated phasestability of Ni-rich Ni-W alloys in terms of the enthalpies of formation andordering energies. We find the chemical pair interactions are sensitive to themagnetic state and concentration. The calculated strain-induced interactionsare quite large for the first coordination shell, which is due to a large sizemismatch of Ni and W. Taking local lattice relaxation into account, the Ni-Wsystems were modeled by Monte Carlo method. The D1a-Ni4W ordered structurecan be observed up to 22 at.% W. In higher concentrations of W, in ourMC calculations, the DO22-Ni3W and Pt2Mo-Ni2W ordered structures can beobserved in Ni-25 at.% W alloy and Ni-33 at.% W alloy, respectively.QC 20160721
34
Edwards, Richard Thornton. "The vapourisation characteristics and metal-mould interactions of high temperature Ni-based superalloys." Thesis, University of Bristol, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390336.
Full text
35
Siva, Prasad Himani. "Selective Laser Melting of Ni-based Superalloys: High Speed Imaging and Process Optimisation." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-59857.
Full textAbstract:
Additive manufacturing is the process of joining or adding material to build an object from 3D model data. Selective Laser Melting (SLM) is an additive manufacturing technology that generates components layer by layer. Though it is already being used in the industry, some aspects are not very well understood. In this thesis, high speed imaging is used to gain new insights about the interaction of laser light with material. A number of parameter sets for high e ciency and good surface finish were found for a nickel based superalloy, HastelloyXTM. Three setups are discussed: single laser pulse interaction with powder, low speed SLM and high speed SLM. It was found, that in order to observe powder behaviour, a narrow bandwidth illumination source is necessary. The low speed SLM process was imaged clearly and revealed three stages of the process, i.e. powder redistribution, melting and drop incorporation. In contrast, the high speed process included vertical powder displacement. Influence of various process parameters is also discussed.
36
Rannou, Benoît. "Slurry coatings from aluminium microparticles on Ni-based superalloys for high temperature oxidation protection." Phd thesis, Université de La Rochelle, 2012. http://tel.archives-ouvertes.fr/tel-00839790.
Full textAbstract:
Because of their good mechanical resistance at high temperature, Ni-based superalloys are used for aero-engine and land-based turbines but undergo "dry" oxidation between 900 and 1500°C. These materials are thus coated with nickel-aluminide coatings (BC). An additional thermal barrier coating (TBC) is generally applied in the hottest sections of the turbines (T>1050°C) to lower the impact of the temperature on the substrate. In the framework of the European research programme "PARTICOAT", this PhD work was focused on the growth mechanisms of a full protective coating system (BC+TBC) in a single step process, using a water-based slurry containing a dispersion of Al micro-particles to satisfy the European environmental directives. The rheological and physico-chemical characterizations showed the slurry stability up to seven days. After depositing the latter by air spraying, a tailored thermal treatment resulted in a nickel-aluminide coating (β-NiAl) similar to the conventional industrial ones but through an intermediate Al liquid phase stage. Simultaneously, the oxidation of the Al micro-particles brought aboutthe formation of a top alumina "foam" (PARTICOAT concept). After a validation step of the mechanisms involved in pure Ni substrate, the extrapolation of the process to several Ni-based superalloys (René N5 (SX), CM-247 (DS), PWA- 1483 (SX) and IN-738LC (EQ)) revealed different coating compositions and microstructures. A particular attention was therefore paid onto the effect of alloying elements (Cr, Ta, Ti) as well as their segregation in the coating. The high temperature behaviour of the coated samples has been studied through isothermal oxidation (1000h in air between 900 and 1100°C) and showed that the oxidation and interdiffusion phenomena ruled the degradation mechanisms. Besides, the electrodeposition of ceria before the application of the PARTICOAT coating allowed to strongly limit interdiffusion phenomena and stabilized the nickel aluminide coating.
37
Yeh, An-Chou. "High temperature phase stability and creep of Ru-bearing Ni-based single crystal superalloys." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615094.
Full text
38
Tréhorel, Roxane. "Comportement mécanique haute température du superalliage monocristallin AM1 : étude in situ par une nouvelle technique de diffraction en rayonnement synchrotron." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0055/document.
Full textAbstract:
Les superalliages monocristallins base nickel sont largement utilisés dans les parties chaudes (aux alentours de 1000°C) des turbines aéronautiques au vu de leur bonne résistance thermomécanique. Pendant le stade II du fluage leur microstructure est formée d’une matrice/couloirs γ (CFC) et de précipités en radeaux γ’ (L12). Le but de cette étude est de mieux comprendre la plasticité de ces matériaux, en particulier celle de l’alliage de 1ère génération AM1. Afin de suivre son comportement mécanique durant des transitions rapides, une nouvelle technique expérimentale par diffraction en transmission des rayons X (synchrotron) a été développée. L’utilisation d’une caméra en champ lointain permet d’enregistrer (une acquisition prend 7 secondes) la tache de diffraction (200) de chacune des deux phases, et donc l’évolution en temps réel du désaccord paramétrique entre les deux phases. En utilisant un modèle mécanique simplifié, il est possible d’en déduire les contraintes internes et la déformation plastique de chaque phase. Une campagne d’essai sur la ligne ID11 de l’ESRF a été réalisée avec cette technique. Deux types d’échantillons présentant une microstructure initiale différente, obtenues par des traitements thermiques adaptés, ont été testés. Ils ont été soumis in situ à des essais de fluage à température constante avec des sauts de contrainte. Après essai, les échantillons ont été caractérisés par MET et MEB afin de déterminer leur microstructure, vérifier les désorientations des échantillons, cartographier la concentration de certains éléments et évaluer la densité de dislocations au sein des radeaux γ’. Dans les couloirs γ, la propagation des dislocations nécessite une contrainte de Von Mises supérieure à la contrainte d’Orowan, et la densité de dislocations mobiles augmente avec la déformation plastique. Le mécanisme limitant la déformation plastique par montée de la phase γ’ est vraisemblablement l’entrée des dislocations dans les radeaux. Les conséquences déduites de cette hypothèse sont détaillées ainsi que le comportement mécanique du matériau résultantNickel-based single crystal superalloys are extensively used for turbines blades (above 1000°C) of aeronautical engines because of their good thermomechanical properties. During stage II of creep, their microstructure consists of a γ matrix (fcc) and raft precipitates γ’ (L12). The aim of this work is to improve the understanding of plasticity of this type of alloy, especially the first generation AM1 superalloy. To follow his mechanical behaviour during fast transients, a new experimental setup using synchrotron radiation diffraction in transmission geometry was developed. A far field camera allows the recording of the (200) diffraction spot of each phase, i.e. the evolution of the lattice misfit in real time (one acquisition takes 7 seconds). By using a simple mechanical model, it is possible to determine the internal stresses and the plastic strains for both phases. An experimental campaign was performed at ID11 beamline of ESRF using this new technique. Two sample types with different initial microstructure (obtained with adapted heat treatments) were tested in situ. They underwent load jumps under high-temperature creep conditions. Further post mortem investigations by SEM and TEM were performed to determine their microstructure, to check on misorientations, map some elements composition and estimate the dislocation density within the γ’ rafts. In the γ channels, dislocation propagation occurred when the Von Mises stress was larger than the Orowan stress. The mobile dislocations density increases with γ plastic strain. The limiting mechanism for γ’ plastic strain is presumably the entry of dislocation within the γ’ rafts. Under this assumption we deduce the mechanisms of interactions between dislocations, vacancies, and pores within the material, and the mechanical behaviour of the γ’ rafts
39
Ahmad, Afandi. "Development of Fe-based Superalloys Strengthened by the γ'Phase." Kyoto University, 2020. http://hdl.handle.net/2433/259045.
Full text
40
Nam, Cheolhee. "Quantitative investigation of solidification in Ni-based superalloys by in-situ X-ray imaging techniques." Kyoto University, 2019. http://hdl.handle.net/2433/245322.
Full text
41
Goswami, Kamal Nayan. "Ab initio study of the effect of solute atoms on vacancy diffusion in Ni-based superalloys." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8509/.
Full textAbstract:
Single crystal Ni-based superalloys are used in the highest temperature components in jet turbine engines owing to their excellent properties under creep conditions. These alloys owe their properties greatly to their chemical composition, and in particular the addition of slow diffusing elements like Re delays the creep deformation significantly. Vacancy diffusion has been suggested to be the rate-controlling process for creep deformation at high temperatures, and elements like Re are expected to interact with the vacancies in slowing them down. This has been investigated in the present work using ab initio calculations. Specifically, dilute as well as non-dilute binary alloys of Re, W and Ta in Ni were considered to study the effect of chemical composition on the rate of vacancy diffusion. Analytical formulations were used to describe the diffusion equations, however their applicability was restricted to the dilute regime. For the calculation of diffusion coefficients particularly in the non-dilute regime, kinetic Monte Carlo simulations were performed. The energies and the diffusion barriers were described using the cluster expansion method. Results suggested appreciable modifications of the vacancy diffusion coefficients, suggesting that the beneficial role of slow-diffusing elements in Ni-based superalloys could be partly explained by their effect on vacancy diffusion.
42
Tézenas, du Montcel Henri. "Ingénierie des joints de grains dans les superalliages à base de nickel." Thesis, Paris, ENMP, 2012. http://www.theses.fr/2012ENMP0006/document.
Full textAbstract:
Ce travail est consacré à l'étude de l'ingénierie des joints de grains dans les superalliages à base de Nickel pour disques de turbines aéronautiques. L'ingénierie des joints de grains a montré son efficacité dans l'amélioration des propriétés en fatigue et en fluage dans certains alliages de cuivre et de nickel. Cette amélioration est obtenue en réalisant une succession de déformations à température ambiante séparées par des traitement thermiques. Ce traitement a pour objectif de modifier la distribution du réseau de joints de grains. L'objectif de l'étude est d'adapter ces traitements au procédé du forgeage à haute température des superalliages. Une étude expérimentale est menée pour mettre en évidence l'influence des paramètres de forgeage sur les caractéristiques du réseau de joints de grains. La caractérisation de ce réseau est faite grâce à la réalisation de cartographies d'orientations cristallographiques par EBSD. Une méthode de caractérisation innovante basée sur la discrétisation des cartographies en réseaux de points triples est proposée. Cette méthode permet d'analyser la connectivité du réseau de joints de grains en vue d'une corrélation avec les propriétés mécaniquesThis work is dedicated to the study of Grain Boundary Engineering in Ni-based superalloys for aircraft turbine disk. The grain boundary engineering has proven its efficiency for the improvement of the fatigue and creep properties of copper and nickel alloys. This improvement is achieved by performing a succession of room temperature deformations interspaced by heat treatments to modify the distribution of the grain boundary network. The aim of the study is to adapt these processes to high temperature forging of superalloys. An experimental study is achieved to highlight the influence of forging parameters on the grain boundary network. The characterization of the grain boundary network is made through the completion of crystallographic orientation mapping by EBSD. An innovative characterization method based on the discretization of orientation maps in a triple junction network is proposed. This method allows to analyze the connectivity in the grain boundary network with the objective of a correlation with mechanical properties
43
Seiser, Bernhard Josef. "Topologically close-packed phase prediction in Ni-based superalloys : phenomenological structure maps and bond-order potential theory." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:4298ebde-4b32-4dcc-b294-649493f9146c.
Full textAbstract:
Single crystal nickel-based superalloys are used in modern gas turbines because of their remarkable resistance to creep deformation at elevated temperatures, which is ensured by the addition of significant amounts of refractory elements. Too high concentrations of refractory elements can lead to the formation of topologically-close packed (TCP) phases during exposure to conditions of high temperature and stress which result in the degradation of the creep properties. The traditional methods for predicting the occurrence of TCP phases in Ni-based superalloys have been based on the PHACOMP and newPHACOMP methodologies which are well-known to fail with respect to new generations of alloys. In this work a novel two-dimensional structure map (Nbar, deltaV/V) for TCP phases where Nbar is the valence-electron count and deltaV/V is a compositional dependent size factor. This map is found to separate the experimental data on the TCP phases of binary, ternary and multi-component TCP phases into well-defined regions corresponding to different structure types such as A15, sigma, chi, delta, P, R, mu, and Laves. In particular, increasing size factor separates the A15, sigma and chi phases from the delta, P, R, mu phases. The structure map is then also used in conjunction with CALPHAD computations of sigma phase stability to show that the predictive power of newPHACOMP for the seven component Ni–Co–Cr–Ta–W–Re–Al system is indeed poor. In order to gain a microscopic understanding of the observed structural trends, namely the differences between the two groups of TCP structures with increasing deltaV/V and the trend from A15 to sigma to chi with increasing Nbar, the electronic structure is coarse-grained from density functional theory (DFT) to tight-binding to bond-order potentials (BOPs). First, DFT is used to calculate the structural energy differences across the elemental 4d and 5d transition metal series and the heats of formation of the binary alloys Mo-Re, Mo-Ru, Nb-Re, and Nb-Ru. These calculations show that the valence electron concentration stabilizes A15, sigma and chi but destablizes mu and Laves phases. The latter are shown to be stabilized instead by relative size difference. Second, a simple canonical TB model and in combination with the structural energy difference theorem is found to qualitatively reproduce the energy differences predicted by the elemental DFT calculations. The structural energy difference theorem rationalizes the importance of the size factor for the stability of the mu and Laves binary phases as observed in the structure map and DFT heats of formation. Finally, analytic BOP theory, is employed to identify the structural origins of the energetic differences between TCP structure-types that lead to the trends found within the two-dimensional structure map.
44
Jullien, Malo. "Étude de la localisation de la déformation à 650°C et de son impact sur la rupture intergranulaire assistée par oxydation : cas de l'Alliage 718." Electronic Thesis or Diss., Ecole nationale des Mines d'Albi-Carmaux, 2024. http://www.theses.fr/2024EMAC0005.
Full textAbstract:
L'Alliage 718 est un superalliage base nickel de référence, largement utilisé dans la fabrication de composants structurels, parfois critiques, tels que les disques de turbine des turboréacteurs. Cet alliage est connu pour fortement localiser la déformation. Cette localisation peut être responsable d'un endommagement précoce en service. Pour le secteur aéronautique, les contraintes écologiques imposent une augmentation des températures de service. Il est alors essentiel d'identifier le rôle que joue le paysage de déformation à l'échelle de la microstructure sur l'endommagement assisté ou non par l'oxydation à ces températures. L'objectif premier de cette thèse est de comprendre comment la microstructure et les vitesses de chargement mécanique affectent le paysage de déformation à haute température. Le second est de lier ce paysage de déformation au comportement mécanique et aux caractéristiques de rupture observées lors d'essais de tractions à 650°C. Les travaux expérimentaux présentés dans ce manuscrit reposent principalement sur la technique de corrélation d'images numériques haute résolution qui permet de capter la réponse mécanique locale de la microstructure sur des régions statistiquement représentatives de la microstructure ; en opposition à des techniques micromécaniques plus locales. Ces travaux ont permis de montrer qu'à 650°C dans l'Alliage 718, la déformation est répartie entre les joints de grains et des bandes de glissement à l'intérieur des grains. Cette répartition dépend à la fois de la sollicitation mécanique et de la microstructure. Une taille de grains grossière favorise le glissement intragranulaire alors qu'une microstructure plus fine favorise la localisation de la déformation aux joints de grains. De même, en traction à faible vitesse de déformation, la localisation aux joints de grains est privilégiée alors qu'à plus haute vitesse de déformation et lorsque le phénomène de Portevin-Le-Chatelier a lieu, le glissement intragranulaire est majoritaire. Lors d'essais de traction sous air à 650°C, seule la localisation aux joints de grains entraine un abattement conséquent de la ductilité. Cependant, plus que l'activité plastique des joints de grains, il est montré que c'est la répartition des événements et leurs interactions qui sont responsables de la rupture intergranulaire assistée par oxydation et la perte de ductilité associée. Cette approche micromécanique associée à l'endommagement local de la matière amène un regard nouveau et intéressant sur le couplage oxydation-mécanique opérant à l'échelle de la microstructure dans cet alliageAlloy 718 is a benchmark nickel-base superalloy, widely used in the manufacture of sometimes critical structural components, such as turbine disks in jet engines. This alloy is known to strongly localize deformation. This localization can be responsible for early damage in service. In the aeronautics sector, environmental constraints mean that service temperatures have to be increased. It is therefore essential to identify the role played by the microstructure-scale deformation landscape on oxidation-assisted or non-assisted damage at these temperatures. The primary objective of this thesis is to understand how microstructure and mechanical loading rates affect the deformation landscape at high temperatures. The second is to link this deformation landscape to the mechanical behavior and fracture characteristics observed in tensile tests at 650°C. The experimental work presented in this manuscript is based mainly on the high-resolution digital image correlation technique, which captures the local mechanical response of the microstructure over statistically representative regions of the microstructure; as opposed to more local micromechanical techniques. This work has shown that at 650°C in Alloy 718, deformation is distributed between grain boundaries and slip bands within the grains. This distribution depends on both mechanical stress and microstructure. A coarse grain size favors intragranular slip, while a finer microstructure favors localization of deformation at grain boundaries. Similarly, at low strain rates, localization at grain boundaries is favored, whereas at higher strain rates and when the Portevin-Le-Chatelier phenomenon occurs, intragranular slip is predominant. In tensile tests in air at 650°C, only localization at grain boundaries results in a significant reduction in ductility. However, more than the plastic activity of grain boundaries, it has been shown that it is the distribution of events and their interactions that are responsible for oxidation-assisted intergranular fracture and the associated loss of ductility. This micromechanical approach, combined with local material damage, provides an interesting new insight into the oxidation-mechanical coupling operating at the microstructural scale in this alloy
45
Karagianni, Eleftheria. "Development of bond coat alloy(s) for Ni based superalloys for low emission gas turbine technology for H2 rich Syngas." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/10585/.
Full text
46
Oskay, Ceyhun [Verfasser]. "Investigation of the microstructural and mechanical property changes of NiAl coated Ni-based superalloys during high temperature exposure / Ceyhun Oskay." Düren : Shaker, 2020. http://d-nb.info/1206855665/34.
Full text
47
Eggeler, Yolita Maria [Verfasser], Sannakaisa [Akademischer Betreuer] Virtanen, and Erdmann [Gutachter] Spiecker. "Nano- and Microstructural Evolution in Ni- and Co-based Single Crystal Superalloys / Yolita Maria Eggeler ; Gutachter: Erdmann Spiecker ; Betreuer: Sannakaisa Virtanen." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2019. http://d-nb.info/1181428564/34.
Full text
48
Schaar, Helge Julian [Verfasser], Ingo [Gutachter] Steinbach, and Jan [Gutachter] Frenzel. "Simulation of solidification on the macro- and microscale in context of Ni-based superalloys / Helge Julian Schaar ; Gutachter: Ingo Steinbach, Jan Frenzel ; Fakultät für Maschinenbau." Bochum : Ruhr-Universität Bochum, 2020. http://d-nb.info/1217860169/34.
Full text
49
Thébaud, Louis. "Etude des relations entre microstructure et propriétés mécaniques du nouveau superalliage base nickel AD730™." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2017. http://www.theses.fr/2017ESMA0033/document.
Full textAbstract:
Compte tenu de l’évolution des températures d’entrée de turbines, le principal enjeu pour les métallurgistes est d’élaborer des alliages capables de présenter d’excellentes propriétés mécaniques à des températures de plus en plus élevées. Dans ce contexte, connaitre les relations entre les différents paramètres microstructuraux et les propriétés mécaniques à haute température (700°C et plus) est capital.La durabilité en fluage et en fatigue-temps de maintien ainsi que les processus d’endommagement de l’alliage AD730™, un nouveau superalliage pour disques de turbines, ont été analysés. Plusieurs paramètres ont été étudiés, qu’ils soient microstructuraux (joints de grains, taille de grains, taille et distribution des précités γ′), ou expérimentaux (température, environnement, contrainte appliquée, temps de maintien). L’utilisation de monograins de composition chimique identique à l’alliage de l’étude a permis de mettre en évidence le fait qu’une microstructure monogranulaire ne présente pas nécessairement de meilleures propriétés en fluage qu’une microstructure polycristalline. Ceci est attribué au rôle durcissant des joints de grains. Il a de plus été montré qu’à 700°C, la taille et la distribution des précipités γ′ est le paramètre microstructural pilotant les propriétés viscoplastiques à l’ordre 1.En fatigue avec temps de maintien, un comportement original a été observé pour les longs temps de maintien en fonction de la contrainte appliquée. Ce phénomène est attribué à un effet « type Bauschinger » apparaissant lors des phases de déchargesIn view of the turbine entry temperature evolution, the main challenge for metallurgists is to elaborate new alloys able to withstand higher temperatures while keeping great mechanical properties. Therefore, knowing the relationships between microstructural parameters and mechanical properties at high temperatures (700°C and more) is mandatory.The creep and dwell-fatigue durability as well as the damage mechanisms of AD730™, a new nickel base superalloy developed for turbine disks, have been analyzed. Several microstructural parameters were studied (grain boundaries, grain size, size and distribution of γ′ precipitates) as well as experimental parameters (temperature, environment, applied stress or dwell period). By using single crystalline specimens having the same chemical composition of the studied alloy, it has been shown unambiguously that single crystalline microstructures do not necessarily present better creep properties compared to polycristalline ones. This result is supposed to be caused by a grain boundary strengthening mechanism. Moreover, in creep at 700°C, it has been shown that the main viscoplasticity controlling parameters are the size and distribution of γ′ precipitates.An unexpected dwell-fatigue behavior has been observed for long hold times and in a specific applied stress window. This phenomena is attributed to a “Bauschinger type” effect, occurring during unloading phases
50
Larrouy, Baptiste. "Mécanismes de déformation et d'amorçage de fissures dans l'alliage Udimet™ 720Li en relation avec les paramètres microstructuraux." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2014. http://www.theses.fr/2014ESMA0019/document.
Full textAbstract:
Cette étude s’est focalisée sur la compréhension des mécanismes de déformation et d’endommagementd’un superalliage à base de Nickel (Udimet 720Li) utilisé pour la confection de disques de turbine hautepression soumis à des sollicitations monotones et cycliques à des températures inférieures à 500 °C.L’amorçage de fissures de fatigue à 20 °C et 465 °C a été systématiquement observé suivant des facettescristallographiques pour différents états métallurgiques. Une étude quantitative des traces de glissementplastique en surface a permis de montrer que cet endommagement est la conséquence d’une nontransmission de la déformation plastique entre grains voisins. Plus précisément, un mécanisme de rotationcristalline localisée au sein de micro-volumes à l’extrémité de bandes de glissement dans le grain voisin aété identifié à l’origine des fissures.Les configurations cristallographiques favorisant ce processus impliquent notamment les relations entresystèmes de glissement de part et d’autre du joint de grains (angle de TWIST), ou encore la présence d’uneprécipitation fine participant au confinement des bandes de glissementThis study contributes to the understanding of the deformation and damage mechanisms in a Nickelbasedsuperalloy (the Udimet 720Li) used for the manufacturing of aeroengines high pressure turbinedisks submitted to monotonic and cyclic loadings at temperatures below 500 °C under service conditions.Fatigue crack initiation at 20 °C and 465 °C was systematically observed at large crystallographic facetswhatever the microstructure. An extensive quantitative study of the slip activity at the surface showed thatcrack initiation results from a difficult slip transmission between neighbouring grains. In more details, alocalized crystallographic rotation confined in micro-volumes detected at the tip of slip bands interactingwith the grain boundary were identified to trigger crack initiation.The crystallographic configurations favouring such a process are closely related to the TWIST anglebetween active slip systems on each side of the grain boundary and to a dense and fine precipitationconfining the plasticity.Mots-clés