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1
Paul, Martin Andrew. "Arc sawing of nickel based superalloys." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396243.
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Rezaei, Hossein. "Diffusion welding of nickel-based superalloys." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186110.
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Ni based superalloys can be welded by diffusion bonding. Temperature, diffusion coefficient, activation energy and Boltzmann constant influence the quality of diffusion bonding, so obtaining the best condition for welding is considered. Showing the suitable condition for diffusion welding of nickel-based superalloys is the aim of this paper.
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Rezaei, Hossein. "Diffusion welding of nickel-based superalloys." Diffusion fundamentals 15 (2011) 2, S. 1-4, 2011. https://ul.qucosa.de/id/qucosa%3A13835.
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Ni based superalloys can be welded by diffusion bonding. Temperature, diffusion coefficient, activation energy and Boltzmann constant influence the quality of diffusion bonding, so obtaining the best condition for welding is considered. Showing the suitable condition for diffusion welding of nickel-based superalloys is the aim of this paper.
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Adegoke, Olutayo. "Homogenization of Precipitation Hardening Nickel Based Superalloys." Thesis, Högskolan Dalarna, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:du-11135.
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Allvac 718 Plus and Haynes 282 are relatively new precipitation hardening nickel based superalloys with good high temperature mechanical properties. In addition, the weldability of these superalloys enhances easy fabrication. The combination of high temperature capabilities and superior weldability is unmatched by other precipitation hardening superalloys and linked to the amount of the γ’ hardening precipitates in the materials. Hence, it is these properties that make Allvac 718 Plus and Haynes 282 desirable in the manufacture of hot sections of aero engine components. Studies show that cast products are less weldable than wrought products. Segregation of elements in the cast results in inhomogeneous composition which consequently diminishes weldability. Segregation during solidification of the cast products results in dendritic microstructure with the segregating elements occupying interdendritic regions. These segregating elements are trapped in secondary phases present alongside γ matrix. Studies show that in Allvac 718Plus, the segregating phase is Laves while in Haynes 282 the segregating phase is not yet fully determined. Thus, the present study investigated the effects of homogenization heat treatments in eliminating segregation in cast Allvac 718 Plus and Haynes 282. Paramount to the study was the effect of different homogenization temperatures and dwell time in the removal of the segregating phases. Experimental methods used to both qualify and quantify the segregating phases included SEM, EDX analysis, manual point count and macro Vickers hardness tests. Main results show that there is a reduction in the segregating phases in both materials as homogenization proceeds hence a disappearance of the dendritic structure. In Allvac 718 Plus, plate like structures is observed to be closely associated with the Laves phase at low temperatures and dwell times. In addition, Nb is found to be segregating in the interdendritic areas. The expected trend of increase in Laves as a result of the dissolution of the plate like structures at the initial stage of homogenization is only detectable for few cases. In Haynes 282, white and grey phases are clearly distinguished and Mo is observed to be segregating in interdendritic areas.
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Curtis, Richard V. "Phase equilibria in recycled nickel-based superalloys." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47013.
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Mathur, Harshal. "Recrystallisation in single crystal nickel-based superalloys." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608207.
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Leidermark, Daniel. "Mechanical Behaviour of Single-Crystal Nickel-Based Superalloys." Thesis, Linköping University, Department of Management and Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-10722.
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In this paper the mechanical behaviour, both elastic and plastic, of single-crystal nickel-based superalloys has been investigated. A theoretic base has been established in crystal plasticity, with concern taken to the shearing rate on the slip systems. A model of the mechanical behaviour has been implemented, by using FORTRAN, as a user defined material model in three major FEM-programmes. To evaluate the model a simulated pole figure has been compared to an experimental one. These pole figures match each other very well. Yielding a realistic behaviour of the model.
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Manson-Whitton, Estelle. "Microstructural evolution of spray formed nickel-based superalloys." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312158.
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Woollin, Paul. "Aspects of fatigue crack growth in nickel-based superalloys." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316765.
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Khan, Sarmad Ali. "Machining of nickel based superalloys using coated PCBN tooling." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5111/.
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Following a comprehensive literature review on the machinability of nickel based superalloys using conventional carbide, coated carbide and ceramics including uncoated/coated PCBN, the research details statistically designed experimental work to assess the tool life/wear performance and workpiece surface integrity of a range of uncoated and coated PCBN tools, when turning solution treated and aged Inconel 718. Typically, the use of carbide tooling is limited to < 60 m/min cutting speed, even with the use of high pressure cutting fluids (JetStream systems). Hardmetal coatings provide some productivity improvements although cutting speed restrictions still operate. Details of PCBN use at up to 600 m/min have been published but at the expense of tool life. Experimental testing of a number of uncoated PCBN grades involving both high and low CBN concentrations, indicated a preferred operating window of ~ 300 – 400 m/min. Advanced ceramic coatings provided no significant benefits. Primary tool wear mechanisms related to abrasion, workpiece adhesion/diffusion and fracture depending on the specific operating parameters employed. In depth workpiece integrity evaluation involving surface roughness, microstructure, microhardness and residual stress measurement suggested only limited damage when operating with PCBN tooling at preferred/optimised conditions.
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Sato, Atsushi. "Nickel-based single crystal superalloys for industrial gas turbines." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3533/.
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The oxidation resistance of four prototype single crystal nickel-based superalloys for industrial gas turbine applications is studied. All contain greater quantities of Cr than in most existing single crystal superalloys; two are alloyed with Si, one with Re. To explain the results, the factors known to influence the rate of Al\(_2\)O\(_3\) scale formation are considered. Models are developed to predict whether any given alloy composition will form a continuous Al\(_2\)O\(_3\) scale. These are used to rationalise the dependence of Al\(_2\)O\(_3\) scale formation on alloy composition in these systems. The mechanical behaviour of a new single crystal nickel-based superalloy for industrial gas turbine applications is also studied under creep and out-of-phase thermomechanical fatigue (TMF) conditions. Neutron diffraction methods and thermodynamic modelling are used to quantify the variation of the gamma prime (\(\gamma\)’) strengthening phase around the \( \gamma\)’ solvus temperature; these aid the design of primary ageing heat treatments to develop either uniform or bimodal microstructures of the \( \gamma\)’ phase. During TMF, localised shear banding occurs with the \( \gamma\)’ phase penetrated by dislocations; however during creep the dislocation activity is restricted to the matrix phase. The factors controlling TMF resistance are rationalised.
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Parimi, Lakshmi Lavanya. "Additive manufacturing of nickel based superalloys for aerospace applications." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/4982/.
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The aim of this work is to establish the influence of the many process variables on the microstructure and the nature of internal stress in IN718 samples produced directly from powder using direct laser fabrication, which enables production of solid samples directly from a CAD file. The process variables that have been studied include, specimen geometry, laser power, laser traverse speed, the detailed laser path and powder feed rate. It has been found that the detailed microstructure is strongly influenced by all of these variables with the propensity for the production of equiaxed or columnar grains being strongly influenced by laser power. The texture is correspondingly strongly influenced by changes in processing conditions. The extent of precipitation of the various phases expected in IN718 was also found to be influenced by the process conditions. The level and nature of the residual stress in the sample and in the substrate have been determined for a wide range of experimental conditions and using neutron diffraction. It has been found that the level of these stresses could be reduced to a minimum value of about 300 MPa, but could not be eliminated. A simple 3D thermo-mechanical model was developed to understand the residual stress distribution, which agreed closely with the experimental measurements.
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Zhu, Zailing. "Analysis and design of nickel-based single crystal superalloys." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:b91e0a91-9f90-4128-9b2b-a608a5128317.
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This thesis provides a research into properties of nickel-based single crystal superalloys. The underlying quantitative relationship between alloy chemistry and the important properties have been studied. To design new grade of single crystal superalloys, computational modelling methods have been proposed which build on the findings of composition-microstructure-property relationships. A physical model for the creep deformation of single crystal superalloys is presented, in which the dependence of the kinetics of creep deformation on alloy chemistry is rationalised. The rate-controlling step is considered to be climb of dislocations at the matrix/particle interfaces and their rate of escape from trapped configurations. The effects of microstructural scale precipitate size, geometry and spacing are also studied. A first order estimate for the rate of creep deformation emerges from the model, which is useful for the purposes of alloy design. Three new single crystal superalloys have been isolated using theory-based computational modelling approaches, termed Alloys-By-Design methods. They are (i) an oxidation-resistant low Re-containing alloy with balanced properties, intended for general-purpose gas turbine applications; (ii) an alloy containing 5.6 wt.% Re and 2.6 wt.% Ru suitable for high performance jet engine applications, and (iii) a cheap, corrosion-resistant alloy for power generation applications. The new alloys have been manufactured using investment casting techniques, and their creep and oxidation behaviour evaluated. The multicomponent composition space pertinent to the single crystal nickel-based superalloys has been mapped and searched, by using newly developed numerical algorithms. This allowed compositions of alloys conferring the microstructures needed for optimal properties to be identified, at a resolution of 0.1 wt.%. Databases have been constructed which contain all appropriate compositions available in these systems. When coupled with composition- and microstructure-dependent property models, the databases can be searched to identify new alloys predicted to exhibit the very best properties or combinations of them.
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Carter, Jennifer Lynn Walley. "Exploration of Local Strain Accumulation in Nickel-based Superalloys." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1344646905.
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Lunt, Matthew James. "The yield stress anomaly and inverse creep in L1â†2 single crystals." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268137.
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Jones, Robert Edward. "Bondcoat developments for thermal barrier coatings." Thesis, Sheffield Hallam University, 1999. http://shura.shu.ac.uk/3137/.
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The prime design considerations for modern nickel based superalloys for use in aero gas-turbine engines, are those of mechanical performance, namely good resistance to creep and fatigue with good toughness and microstructural phase stability. Design of the current generation of superalloys has attained these properties at the expense of environmental resistance. This design philosophy has lead to the widespread use of surface coatings technology to protect hot-section componentry from the harsh operating environment. The ongoing drive towards higher operating temperatures has lead to an interest, over the last few years, in thermal barrier coatings (TBCs). TBCs are duplex coating systems consisting of a thin, insulating, ceramic layer over a metallic bondcoat. The bondcoat provides both environmental protection and the necessary adhesive interface to maintain the adherence of the ceramic during the rigours of operation. Central to the performance of a TBC system is the integrity and adherence of the alumina scale promoted by the bondcoat. This study aimed to design and optimise a novel bondcoat system that was capable of out-performing the current generation of bondcoats and progress the resultant coating into a production ready status. This was achieved by comparing the performance of a range of bondcoats of both novel and standard compositions, using the modified scratch test in conjunction with hot isothermal and cyclic furnace tests. The down selected system was then analysed using a range of techniques including optical and electron microscopy, XRD, WDS and SIMS in order to understand the failure mechanisms. The results of the testing programme lead to bondcoat chemistry changes and processing improvements that enabled better performance to be achieved. The bondcoat was optimised and taken to a production standard by using the Taguchi Method of fractional factorial experimental design. The resultant coating system offered a higher TBC/bondcoat interface temperature capability and extended the life of the system at more moderate temperatures, beyond that offered by systems currently available. The coating system has subsequently been run as a bondcoat for EB-PVD TBCs and has successfully completed the duty cycles on a number of development and test engines.
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Wang, Wei. "A mathematical model of dendritic microstructures in nickel-based superalloys." Thesis, Imperial College London, 2003. http://hdl.handle.net/10044/1/11524.
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Xu, Xuahua. "Grain development during vacuum arc remelting of nickel based superalloys." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368958.
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Tung, David C. "Welding Metallurgy of Nickel-Based Superalloys for Power Plant Construction." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1449164834.
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Németh, André Anjou Nordine. "Environmentally-assisted fracture events in high strength nickel-based superalloys." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:e2bb3d1f-06cd-4c6a-addc-f217d1eeddc7.
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There is significant interest in defining and quantifying the performance of polycrystalline Ni-based superalloys - particularly high strength ones produced via powder processing for turbine disc applications - at temperatures between 700 and 800°C. This is because the outer rims of a high pressure turbine disc in turbine applications for jet propulsion can experience such temperatures during a significant portion of the flight cycle while also being exposed to oxidative/corrosive gases which cause intergranular environmentally-assisted crack growth. In this work, a testing methodology involving slow strain-rate tensile tests on a electro-thermal mechanical testing device is presented which is capable of the rapid assessment of an alloys susceptibility to environmentally-assisted cracking. It makes use of miniature test pieces which are shown to be of sufficient size to characterise macroscopic properties. This approach is first validated and then utilized to perform systematic experimentation involving the control of the important microstructural and compositional variables such that the effects of others can be isolated, identified and confirmed. The need to better understand the embrittlement mechanism was addressed at the most appropriate lengthscale using high resolution characterisation techniques which are capable of providing the most revealing information including scanning and transmission electron microscopy and nanoscale secondary ion mass spectrometry. Our results have implications for alloy design efforts â rationalising the effect of heat treatment and demonstrating that for a given strength level, both more and less damage tolerant variants can be designed.
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Yang, Jian. "Microstructure-property development in linear friction welding of nickel-based superalloys." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5567/.
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Linear friction welding (LFW) is known as an advanced technique to substitute fusion welding of joining Ni-based superalloys. However, due to the complex microstructural development caused by LFW, some unexplained issues still need to be solved, such as: influence of weld parameters (weld pressure, amplitude of oscillation, and frequency of oscillation) on the development of microstructural, microhardness, texture and residual stresses in LFWed IN718-IN713LC; impact of post-weld heat treatment (PWHT) on the microstructural and microhardness development; influence of rapid thermal cycle on the precipitate dissolution of IN718 and IN713LC; formation mechanisms of alumina inclusions (Al-oxides) on the weld interface. The present work aims to investigate these issues.
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Tapia, Alma Stephanie. "Computational design of nickel based superalloys for industrial gas turbine components." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013180.
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Cancho, Daniel Barba. "Segregation-assisted creep in nickel-based superalloys : experiments, theory and modelling." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:33e157e8-0e68-49b1-9225-12f8a2039dee.
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Mid-temperature creep deformation in the range of 600 to 850°C is assuming greater importance in Ni-based superalloys. This is because the design operating temperature of the combustion cycle is increasing as the new generations turbofan engines become more efficient. The temperature at the rim of turbine disks and the root of turbine blades can be in this critical range of temperatures for significant portions of the mission cycle, leading to a complex time-dependent mode of plasticity called "microtwinning"'. Unfortunately this kind of coupled displacive-diffusive deformation mechanism is not yet well understood, and even the range of temperatures and stresses where microtwinning occurs is not clearly defined. This work explores the fundamentals of this phenomenon, from the kinetics of microtwinning to its influence on the mechanical behaviour of the material. To achieve this objective, coupled computational-experimental studies have been carried out. First, the contribution of microtwinning mechanism to the creep deformation of a single crystal superalloy is studied. The accumulated creep strain computed from quantitative stereology of the tested samples supports the role of this mechanism in conferring plastic deformation. Second, the chemical composition of the microtwins is analysed by means of atomic-resolution characterisation techniques (APT and TEM). Segregation of Î3'-stabilisers to the growing faults is found to be crucial for the understanding of the creep mechanisms in this range of temperatures. Third, a model for diffusion-controlled growth of microtwins is proposed and used to recover the experimental creep strain rates. This then provides the basis for a thermodynamically consistent constitutive model developed on the basis of crystal plasticity theory. The constitutive model is subsequently implemented into a finite element code to study the activation of the different plastic mechanisms within single crystal and polycrystalline aggregates depending on the crystal orientation. With the support of this model, a relation between the rotations of the crystal and the creep life of the different crystal orientations is established. The numerical and experimental results ultimately reveal the critical role of the microtwinning on the asymmetric behaviour of the alloy and thus, its influence on the mechanical performance.
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Köksal, Sakip. "Face milling of nickel-based superalloys with coated and uncoated carbide tools." Thesis, Coventry University, 2000. http://curve.coventry.ac.uk/open/items/86a6b065-704a-475b-b805-9d3397487ddf/1.
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Face milling machinability investigation of two difficult-to-machine nickel-based superalloys, namely Inconel 718 and Waspaloy, has been carried out with four different types of tungsten carbide tools under various cutting conditions. The tools comprised of one double-layer CVD-TiCN+Al2O3 coated (KC994M), two PVD-TiN coated (KC720 and KC730) and one uncoated (KMF) tungsten carbide tools. The objectives of the study include investigation of tool performance, failure modes and wear mechanisms under the cutting conditions employed. In addition, surface integrity of the machined surfaces, with regard to surface finish, subsurface microhardness and metallographic examination of the subsurface microstructure, was investigated. CVD-coated KC994M gave the best overall performance in terms of tool life at low and high cutting conditions on both workpieces. The second best-performing tool was the uncoated KMF grade which gave as high tool lives as KC994M at lower cutting speeds. However at higher cutting speeds, KMF was generally outperformed by PVD-TiN coated tools. Short tool lives were obtained at higher cutting speeds of 75 and 100 m/min due to premature failure by chipping. Tool wear at low cutting speed range was due to a combination of progressive microchipping and plucking through a fracture/attrition related wear mechanism associated with cyclic workpiece adhesion and detachment and abrasion/diffusion-related flank wear. Plucking and microchipping were the dominant wear mechanisms. Coating layers on the rake face of both CVD and PVD coated tools were almost completely removed within the first few seconds of cutting at all cutting speeds tested, thus becoming ineffective. On the flank face, however, they remained intact for a longer period and hence increasing tools performance at the medium cutting speed range. Analysis of the subsurface microstructures and microhardness measurements showed that plastic deformation was the predominant effect induced onto the machined surface, the degree of which influenced by the cutting speed, tool wear and prolonged machining. In addition surface irregularities in the form of tearing and embedded hard particles were found to occur which was mainly associated with the chipping dominated wear mode.
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Sadiq, Saqib. "Intermetallic compond precipitation in some model nickel based superalloys containing refractory metals." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/46416.
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Busuttil, Markus. "The influence of glass coating on the forging of nickel-based superalloys." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/4870/.
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Forging of components for gas turbine application from nickel-based superalloys remains a challenge, due to the exceptional high temperature properties of these alloys. In order to enhance formability and prevent oxidation at high temperature forging, a glass coating is applied to protect the alloy. However, the contribution and significance of glass coating to the material flow during forging is not fully understood. In addition, increased competitive pressure requires a better understanding of the root cause for geometrical part variability in the forging of aerospace components. Particularly, reduction of manual rework is highly desirable, as it increases the manufacturing costs of these components significantly. The aim of this work was to identify the Key Process Variables (KPVs) of the forging of aerofoils. Therefore, numerical modelling of a full factorial design of experiment was conducted to study the significance of various process parameters. The contribution of glass coating as a process variable has been studied experimentally. The double cup extrusion test has been employed to study the influence of glass coating thickness and chemistry in hot forging condition. Ring compression tests have been conducted to investigate the contribution of graphite lubricant. It was found, that in the presence of graphite lubricant friction reduces markedly. However, in order to establish a stable lubrication system the fusion behaviour of glass coating becomes crucial. In the absence of graphite lubricant, friction increases with increased glass coating thickness. Numerical modelling revealed that the interfacial heat transfer coefficient increases with a reduction of glass coating thickness. A good agreement between experimentally and numerically derived interfacial heat transfer coefficient has been found. In contrast, in a rapid deformation process such as blade forging, the effect of heat loss becomes less important compared to the contribution of friction. The initial variability of glass coating thickness has been characterised in the industrial forging of Inconel 718 aerofoils. Glass coating thickness varies considerably across the workpiece and the batch. This variability, alongside the variability of manual process parameters such as transfer and resting time, have a notable effect on the forming temperature and thus on the resulting aerofoil geometry.
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Schoettle, C. "Sustained macroscopic defelcted cracking in nickel based superalloys : mechanism and design criteria." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/355954/.
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In this EngD thesis the phenomenon of sustained macroscopic deflected crack growth (SMDCG) during fatigue in Nickel based Superalloys is discussed, also referred to as ‘teardrop’ cracking in previous work. In a corner notched bend (CNB) specimen a fatigue crack usually grows in a quarter-circular plane perpendicular to the stress axis, the SMDCG however exhibits considerable deflection from this plane at the free surfaces, so that a central planar region is enclosed by large shear terraces (thus forming the ‘teardrop’). This is difficult to characterise in terms of component lifing (both in terms of crack path and crack growth rates), and this thesis aims to further understanding of the underlying mechanisms and to develop assessment methodologies for lifing of such cracks in aeroengine components. The SMDCG effect has been observed under externally applied mode I loading in Udimet 720Li with relatively fine grain sizes of 6-18μm, which are candidate materials for aero engine turbine discs. CNB and single edge bend notch bend (SENB) fatigue tests have been carried out on cast and wrought and powder metallurgy variants of Udimet 720Li and SMDCG was observed at 300°C in air and at 300, 600 and 650°C in vacuum. A consistent measure of the onset of deflection has been defined; this is the crack tip stress intensity factor range K at which the sustained deflection from the free surface exceeds the expected shear lip area, which is estimated as the distance of the monotonic plane stress plastic zone size from the free surface. This has been used to characterise samples from other research programmes and aeroengine components from rigtests, that have shown some form of deflected crack growth, to assess whether they exhibit SMDCG or whether the apparent deflection was caused by the expected plane stress region, or other factors such as tunnelling due to creep effects or complex overall loading conditions. Fracture surfaces exhibiting SMDCG have been studied via SEM and the fractographic analysis shows a competition between local shear crack growth and mode I crack growth occurs in both the macroscopically deflected and planar regions. This indicates that the macroscopic deflection is triggered by the stress state at the free surface. Further detailed analysis of the deflected crack tip with focussed ion beam (FIB) serial sectioning combined with EBSD analysis has allowed a detailed 3D reconstruction of the crack tip interaction with local microstructure. This, together with TEM foils extracted via FIB in the same region, have confirmed that the SMDCG in these systems is not linked to any local texture effects or surface microstructural differences. Lifetime predictions for the CNB samples have been carried out based on Paris law coefficients from the SENB tests, and showed shorter lifetimes than the actual samples with deflected crack growth. Whilst this could be partially due to unaccounted for initiation effects, it could also indicate that significant extrinsic shielding caused by the deflected crack growth may actually increase fatigue lifetimes. To assess the driving force evolving during SMDCG, an Alicona Infinite Focus profilometre has been used to map the complex 3D crack shapes, from where tilt angles could be measured to define a mixed mode plane stress SENB test, with the aim of replicating the stress state that had given rise to the locally deflected shear growth and to explicitly measure crack growth behaviour in the deflected regions. However this was not achieved with this test set-up, as the achievable ΔKeff was not high enough to trigger the deflection throughout the sample. As a result the 3D map was next used to define Finite Element model to assess the local crack tip stress state of the complex deflected crack path. Crack driving forces that have been identified at the point the deflected crack path becomes self-sustaining, could be used in a lifing model to predict crack paths in aeroengine components, together with the measured onset of deflection.
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Aslan, Ozgur. "Numerical modeling of fatigue crack growth in single crystal nickel based superalloys." Paris, ENMP, 2010. http://pastel.archives-ouvertes.fr/pastel-00540893.
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Les composants monocristallins fonctionnant à des températures élevées sont soumis à des conditions de chargement thermo-mécanique sévères. La géométrie et le comportement de ces composants sont très complexes. Un défi majeur est de développer des modèles mathématiques afin de prévoir l'initiation et la propagation de fissures en présence de contraintes importantes et de forts gradients de température. Dans ce cas, le comportement élastoviscoplastique fortement anisotrope du matériau étudié (superalliage à base Ni) doit être pris en compte. Le modèle correspondant doit être en mesure de rendre compte de la croissance anisotrope des fissures et de leur bifurcation dans des champs de contrainte complexes. De plus, le modèle doit être capable de prédire non seulement le taux de croissance des fissures mais aussi les chemins de fissuration. La mécanique de l'endommagement anisotrope est un cadre théorique bien adapté au développement de modèles de croissance de fissures dans les monocristaux. Au cours d'études précédentes, une loi de comportement couplant plasticité cristalline et endommagement cyclique a été développée, démontrant l'intérêt de cette approche, mais aussi ses limites, notamment du fait de la dépendance au maillage des résultats. Le développement récent de modèles non-locaux dans le cadre de la mécanique des milieux continus pourrait ainsi aider à surmonter ces difficultés. Une grande base expérimentale existe concernant l'initiation et la propagation de fissures dans les superalliages monocristallins à base de nickel. Les simulations thermomécaniques par éléments finis des aubes de turbine fournissent des informations détaillées sur la distribution des contraintes et des déformations plastiques, en particulier près de singularités géométriques comme les trous et les fentes de refroidissement. Tout d'abord, sur la base de la théorie de la plasticité cristalline qui établit un lien solide entre les contraintes et les déformations plastiques, un modèle découplé en mécanique de l'endommagement basé sur l'historique des calculs par éléments finis sera présenté. Ensuite, un modèle d'endommagement incrémental basé sur les milieux généralisés sera proposé et enfin, les prédictions du modèle pour l'initiation et la croissance de micro-fissures en résolvant le problème de dépendance au maillage seront discutésSingle crystal components operating at elevated temperatures are subjected to severe thermomechanical loading conditions. The geometry and behaviour of these components are now very complex. A major issue is to develop models to predict crack initiation and crack growth in the presence of strong stress and temperature gradients. The strongly anisotropic elastoviscoplastic behaviour of the material which is a single crystal nickel base superalloy, must be taken into account. The corresponding model should be able to account for anisotropic crack growth and crack bifurcation in complex stress elds. Moreoever the model must be capable of predicting not only the crack growth rate but also the non-straight crack paths. Anisotropic damage mechanics is a well-suited theoretical framework for the development of crack growth models in single crystals. A model coupling crystal plasticity and cyclic damage has been developed in a previous project, that shows the interest of the approach, but also its current limits, in particular the strong mesh dependence of the results. Recent development of nonlocal models within the framework of the mechanics of generalized continua could help overcoming these difficulties. A large experimental basis exists concerning initiation and crack growth in single crystal nickel base superalloys. Finite element simulations of the thermomechanics of turbine blades provide detailed information about stress and plastic strain distribution, in particular near geometrical singularities like cooling holes and slits. First of all, on the basis of crystal plasticity theory which provides a solid link between stress and plastic strains, an uncoupled damage mechanics model based on the history of FE calculations will be presented. Afterwards, an incremental damage model based on generalized continua will be proposed and model predictions for the initiation and growth of microcracks by solving the mesh dependency, will be discussed
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Payton, Eric John. "Characterization and Modeling of Grain Coarsening in Powder Metallurgical Nickel-Based Superalloys." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1250265477.
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Po-Sri, Chatuporn. "Elevated temperature crack growth in inertially welded nickel-based superalloys and gamma based titanium aluminides." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/1432/.
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An evaluation of inertia friction welds in RR1000 has been conducted through microtensile and sustained load crack growth tests on pre-cracked testpieces. As-welded and two post weld heat treatment conditions have been considered. The fatigue crack growth behaviour of γ TiAl has also been considered, with a focus on establishing fatigue crack growth thresholds.
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Bloss, Matthew C. "Ultrasonic metal welding the weldability of stainless steel, titanium, and nickel-based superalloys /." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1198168491.
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Cosentino, Francesco. "Heat treatment of nickel based superalloys for turbine blade application : modelling and validation." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4250/.
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A numerical model has been developed for the simulation of the vacuum heat treatment and high pressure gas quenching used during the manufacture of single crystal turbine blades, of the type used for aeroengine applications. Heat transfer by radiation and forced convection is taken into account to obtain quantitative predictions of the thermal history of the components during ramping-up, holding and gas fan quenching. The uniformity of the temperature is investigated and the effectiveness of the treatment is assessed. Simulations of the quenching process have allowed visualisation of the flow field and prediction of the local quench rate as a function of the furnace parameters. The results of the modelling have been validated against thermocouple measurements made on laboratory-scale vacuum furnace with many of the characteristics of the type used in industrial production. The modelling methodology is extended to industrial scale processes via a multi-scale decomposition approach. The effect of quench rate on the microstructure of CMSX-10 has been characterised using scanning electron microscopy. It is shown that the precipitate size distribution correlates directly with the local quenching rate. To understand the influence of the microstructure on creep performance, two structures with different average \(\gamma\)’ size have been tested in creep over a wide range of temperatures and applied stress levels. Particularly in the low temperature / high stress regime, the size of the precipitates markedly determines the creep performance observed.
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Xu, Jinghao. "Alloy Design and Characterization of γ′ Strengthened Nickel-based Superalloys for Additive Manufacturing." Licentiate thesis, Linköpings universitet, Konstruktionsmaterial, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-173042.
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Nickel-based superalloys, an alloy system bases on nickel as the matrix element with the addition of up to 10 more alloying elements including chromium, aluminum, cobalt, tungsten, molybdenum, titanium, and so on. Through the development and improvement of nickel-based superalloys in the past century, they are well proved to show excellent performance at the elevated service temperature. Owing to the combination of extraordinary high-temperature mechanical properties, such as monotonic and cyclic deformation resistance, fatigue crack propagation resistance; and high-temperature chemical properties, such as corrosion and oxidation resistance, phase stability, nickel-based superalloys are widely used in the critical hot-section components in aerospace and energy generation industries. The success of nickel-based superalloy systems attributes to both the well-tailored microstructures with the assistance of carefully doped alloying elements, and the intently developed manufacturing processes. The microstructure of the modern nickel-based superalloys consists of a two-phase configuration: the intermetallic precipitates (Ni,Co)3(Al,Ti,Ta) known as γ′ phase dispersed into the austenite γ matrix, which is firstly introduced in the 1940s. The recently developed additive manufacturing (AM) techniques, acting as the disruptive manufacturing process, offers a new avenue for producing the nickel-based superalloy components with complicated geometries. However, γ′ strengthened nickel-based superalloys always suffer from the micro-cracking during the AM process, which is barely eliminated by the process optimization. On this basis, the new compositions of γ′ strengthened nickel-based superalloy adapted to the AM process are of great interest and significance. This study sought to design novel γ′ strengthened nickel-based superalloys readily for AM process with limited cracking susceptibility, based on the understanding of the cracking mechanisms. A two-parameter model is developed to predict the additive manufacturability for any given composition of a nickel-based superalloy. One materials index is derived from the comparison of the deformation-resistant capacity between dendritic and interdendritic regions, while another index is derived from the difference of heat resistant capacity of these two spaces. By plotting the additive manufacturability diagram, the superalloys family can be categorized into the easy-to-weld, fairly-weldable, and non-weldable regime with the good agreement of the existed knowledge. To design a novel superalloy, a Cr-Co-Mo-W-Al-Ti-Ta-Nb-Fe-Ni alloy family is proposed containing 921,600 composition recipes in total. Through the examination of additive manufacturability, undesired phase formation propensity, and the precipitation fraction, one composition of superalloy, MAD542, out of the 921,600 candidates is selected. Validation of additive manufacturability of MAD542 is carried out by laser powder bed fusion (LPBF). By optimizing the LPBF process parameters, the crack-free MAD542 part is achieved. In addition, the MAD542 superalloy shows great resistance to the post-processing treatment-induced cracking. During the post-processing treatment, extensive annealing twins are promoted to achieve the recrystallization microstructure, ensuring the rapid reduction of stored energy. After ageing treatment, up to 60-65% volume fraction of γ′ precipitates are developed, indicating the huge potential of γ′ formation. Examined by the high-temperature slow strain rate tensile and constant loading creep testing, the MAD542 superalloy shows superior strength than the LPBF processed and hot isostatic pressed plus heat-treated IN738LC superalloy. While the low ductility of MAD542 is existed, which is expected to be improved by modifying the post-processing treatment scenarios and by the adjusting building direction in the following stages of the Ph.D. research. MAD542 superalloy so far shows both good additive manufacturability and mechanical potentials. Additionally, the results in this study will contribute to a novel paradigm for alloy design and encourage more γ′-strengthened nickel-based superalloys tailored for AM processes in the future.Additional funding agencies: Agora Materiae Graduate School for multidisiplinary PhD students at Linköping University, and Stiftelsen Axel Hultgren.
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Segersäll, Mikael. "Nickel-Based Single-Crystal Superalloys : the crystal orientation influence on high temperature properties." Licentiate thesis, Linköpings universitet, Konstruktionsmaterial, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-89950.
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Superalloys are a group of materials that are used in high temperature applications, for example gas turbines and aero engines. Gas turbines are most commonly used for power generation, and it is only the very critical components which are exposed to the most severe conditions within the turbine, which are made from superalloy material. Today, energy consumption in many parts of the world is very high and is tending to increase. This implies that all power generating sources, including gas turbines, must aim for higher efficiency. For the gas turbine industry, it is a continuous challenge to develop more energy-efficient turbines. One way to do this is to increase the temperature within the hot stage of the turbine. However, increased temperature in the hot stage also challenges the materials that are used there. Today’s materials are already pushed to the limit, i.e. they cannot be exposed to the temperatures which are required to further increase the turbine efficiency. To solve this problem, research which later can lead to better superalloys that can withstand even higher temperatures, has to be conducted within the area of superalloys. The aim of this licentiate thesis is to increase our knowledge about deformation and damage mechanisms that occur in the microstructure in superalloys when they are subjected to high temperatures and loads. This knowledge can later be used when developing new superalloys. In addition, increased knowledge of what is happening within the material when it is exposed to those severe conditions, will facilitate the development of material models. Material models are used for FEM simulations, when trying to predict life times in gas turbine components during the design process. This licentiate thesis is based on results from thermomechanical fatigue (TMF) testing of Ni-based single-crystal superalloys. Results show that the deformation within the microstructure during TMF is localized to several deformation bands. In addition, the deformation mechanisms are mainly twinning and shearing of the microstructure. Results also indicate that TMF cycling seems to influence the creep rate of single-crystal superalloys.
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Ellis, Jonathan Dudley. "Quality assurance by electron beam button melting." Thesis, Imperial College London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286213.
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Knaggs, Craig. "Effects of surface condition on fatigue in nickel-based superalloys for aero-engine applications." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7495/.
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Resistance against fatigue failure is a major requirement for critical rotating parts, which could be sensitive to surface condition after machining such as roughness, modification of microstructure and residual stress. The speed, tool material and other machining parameters can also have a significant effect on the surface quality of the parts. The effects of baseline and damage machining on the surface integrity of Alloy 720Li have been characterised comprehensively using metallography, EDX, surface roughness, micro hardness, nano-indentation, electron backscattered diffraction, differential scanning calorimetry and transmission electron microscopy. It was found that machining damage imparted a work-hardened layer, poorer surface roughness and surface features containing recrystallised material. A test matrix was constructed to establish whether machining induced changes of surface integrity would impact the fatigue performance of the material. Baseline samples and samples damaged by machining both with and without shot peening, and at different Kt factors were tested. Low cycle fatigue tests were conducted. Some damage machined samples exhibited a lower fatigue life. This was attributed to brittle surface features, caused by high temperatures and forces of machining, which resulted in early crack initiation.
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Aluru, Sreenivasa Charan Rajeev Gale W. F. "Microstructure - mechanical property relationships in transient liquid phase bonded nickel-based superalloys and iron-based ODS alloys." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Spring/doctoral/ALURU_SREENIVASA_32.pdf.
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Després, Mélissa. "On the evaluation of ductile behaviour of porous nickel-based superalloys using finite element method." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=83860.
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The present work aims to assess the ductile behaviour of porous Inconel 625 nickel-based superalloys, produced by Metal Injection Moulding (MIM). A qualitative study of the local behaviour was conducted through a series of simple finite element models. Obtained results have been analyzed and compared to more common materials. The following study focuses on the strain localization phenomenon leading to ligament failure between 2 pores relative to their dimensions, their orientation, the distance separating them and the triaxiality ratio. Obtained results demonstrated that the dimensions of the plastic zone in the neighbourhood of pores proportionally increase with pore diameter. Hence, it has been shown that in the case of Inconel 625, the localization was more pronounced between 2 pores whose relative orientation is 0º. Furthermore, it was possible to observe that the critical far-field strain corresponding to the onset of flow localisation between two pores was decreasing as the distance between them was diminishing. By comparing the behaviour of Inconel 625 with that of aluminium 7075-T6, it has been shown that the amplification of the plastic strains was lower in the case of Inconel 625 and consequently the onset of strain localisation (i.e.ligament failure) was found to be delayed in comparison with aluminium. Hence, the high work hardening coefficient of Inconel 625 reduces its sensitivity to the presence of pores. It has thus been shown that Inconel 625 MIM has mechanical properties superior to the equivalent cast material.
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SIVO, ANTONIO. "On the Laser Powder Bed Fusion based processing route for hard to weld Nickel Superalloys." Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2971609.
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Grant, Benedict M. B. "Finite Element Modelling of Inertia Friction Welding Advanced Nickel-Based Superalloys Using an Energy Balancing Approach." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505492.
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Fisk, Joseph Charles. "Effects of creep and oxidation interaction on high temperature crack growth behaviour of nickel based superalloys." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4572/.
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A complete and comprehensive understanding of dwell crack growth behaviour is required for two compressor and turbine disc alloys, Udimet 720Li and RR1000, both having a fine grain microstructure. The effect of temperature, dwell time and dwell load has been studied in air and vacuum along with detailed fractographic and microstructural analysis to understand the relevant contributions of oxidation, creep and microstructure. The study has been extended to determine the effect of an overload segment in the load waveform, the rationale being that this type of waveform better models real loading cycles on engines in service. In support with extensive modelling carried out within Rolls-Royce plc in order to understand the stress state ahead of the crack tip and its relaxation over dwell time, the effect of overload factor, test temperature and dwell time has also been examined empirically. In good agreement with the findings of others, crack growth rates according to overload cycling are shown to propagate significantly slower than crack growth rates according to (otherwise similar) dwell-only loading, or static loads; even at high temperature and in an oxidising environment. A good agreement between modelled predictions and experimental results has been achieved, indicating that the retardation of crack growth rates is mainly affected by mechanical factors.
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Chaudhari, Mrunalkumar. "First Principles Calculations of the Site Substitution Behavior in Gamma Prime Phase in Nickel Based Superalloys." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc149571/.
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Nickel based superalloys have superior high temperature mechanical strength, corrosion and creep resistance in harsh environments and found applications in the hot sections as turbine blades and turbine discs in jet engines and gas generator turbines in the aerospace and energy industries. The efficiency of these turbine engines depends on the turbine inlet temperature, which is determined by the high temperature strength and behavior of these superalloys. The microstructure of nickel based superalloys usually contains coherently precipitated gamma prime (?) Ni3Al phase within the random solid solution of the gamma () matrix, with the ? phase being the strengthening phase of the superalloys. How the alloying elements partition into the and ? phases and especially in the site occupancy behaviors in the strengthening ? phases play a critical role in their high temperature mechanical behaviors. The goal of this dissertation is to study the site substitution behavior of the major alloying elements including Cr, Co and Ti through first principles based calculations. Site substitution energies have been calculated using the anti-site formation, the standard defect formation formalism, and the vacancy formation based formalism. Elements such as Cr and Ti were found to show strong preference for Al sublattice, whereas Co was found to have a compositionally dependent site preference. In addition, the interaction energies between Cr-Cr, Co-Co, Ti-Ti and Cr-Co atoms have also been determined. Along with the charge transfer, chemical bonding and alloy chemistry associated with the substitutions has been investigated by examining the charge density distributions and electronic density of states to explain the chemical nature of the site substitution. Results show that Cr and Co atoms prefer to be close by on either Al sublattice or on a Ni-Al mixed lattice, suggesting a potential tendency of Cr and Co segregation in the ? phase.
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Lawitzki, Robert [Verfasser], and Guido [Akademischer Betreuer] Schmitz. "Analysis of nickel- and iron-based superalloys on smallest length scales / Robert Lawitzki ; Betreuer: Guido Schmitz." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2021. http://d-nb.info/1236574044/34.
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Strand, Emil, and Alexander Wärnheim. "A study of micro- and surface structures of additive manufactured selective laser melted nickel based superalloys." Thesis, KTH, Materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-188154.
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This study examined the micro- and surface structures of objects manufactured by selective laser melting (SLM). The results show that the surface roughness in additively manufactured objects is strongly dependent on the geometry of the built part whereas the microstructure is largely unaffected. As additive manufacturing techniques improve, the application range increases and new parameters become the limiting factor in high performance applications. Among the most demanding applications are turbine components in the aerospace and energy industries. These components are subjected to high mechanical, thermal and chemical stresses and alloys customized to endure these environments are required, these are often called superalloys. Even though the alloys themselves meet the requirements, imperfections can arise during manufacturing that weaken the component. Pores and rough surfaces serve as initiation points to cracks and other defects and are therefore important to consider. This study used scanning electron-, optical- and focus variation microscopes to evaluate the microstructures as well as parameters of surface roughness in SLM manufactured nickel based superalloys, Inconel 939 and Hastelloy X. How the orientation of the built part affected the surface and microstructure was also examined. The results show that pores, melt pools and grains where not dependent on build geometry whereas the surface roughness was greatly affected. Both the Rz andRa values of individual measurements were almost doubled between different sides of the built samples. This means that surface roughness definitely is a factor to be considered when using SLM manufacturing.
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Malush, Rudolph E. "An investigation of the hot corrosion protectivity behavior of platinum modified aluminide coatings on nickel-based superalloys." Thesis, Monterey, California: U.S. Naval Postgraduate School, 1987. http://hdl.handle.net/10945/22321.
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Simmonds, Scott. "Formation and avoidance of surface defects during casting and heat-treatment of single-crystal nickel-based superalloys." Thesis, University of Leicester, 2014. http://hdl.handle.net/2381/28806.
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Nickel-based superalloys are a class of materials that have been specifically developed for high temperature applications for use in aero-engines and power generation. The evolution of superalloy chemistry and solidification structure has made the control and prevention of defect formation in single-crystal components increasingly challenging. This study examines the formation and avoidance of Surface Scale and Surface Melting, both of which are detrimental to the production cost and the performance of single-crystal turbine components. Surface Scale is a defect found on the surface of as-cast single-crystal components identified as a region of discolouration. A systematic analysis reveals that Surface Scale forms in the solid-state during casting due to the combined effects of (1) differential thermal contractions between mould and metal and (2) transient oxidation of the exposed metal casting surface at temperature below ~1300°C. The resultant transient oxide film is 0.5-1μm thick whilst the remaining surface undergoes a mould-metal reaction during the initial stages of casting, at temperatures above the liquidus, producing a 1-2μm thick protective layer of Al[subscript 2]O[subscript 3]. Surface Melting is identified on the heat-treated blade surface as an area of localised melting within the Scaled surface area. Through an in-depth analysis of the microstructural evolution it was found that Surface Melting is a consequence of elemental evaporation of γ-phase stabilisers. The subsequent change in chemistry results in the transformation of the γ phase to γ’ and TCPs and a concomitant occurrence of incipient melting at the surface during solution heat treatment. This thesis concludes that the prevention of Surface Scale is made possible by the use of an inert atmospheric gas, such as Argon, within the casting furnace. However, the subsequent formation of Surface Melting during heat-treatment can only be prevented by pre-oxidising the as-cast components, thus forming Al[subscript 2]O[subscript 3] in order to form a protective barrier to evaporation.
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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.
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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
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Léglise, Mélissa. "Amélioration des propriétés mécaniques et chimiques de superalliages base nickel et base cobalt de fonderie utilisés pour le fibrage du verre fondu à 1000°C - 1100°C." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0228.
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Les assiettes de fibrage utilisées pour la production de fibres de verre subissent d’importantes contraintes mécaniques, chimiques et thermiques. Par conséquent, cette pièce se dégrade et doit être périodiquement remplacée. Le but de ces travaux est d’augmenter la durée de vie des assiettes de fibrage en améliorant les propriétés mécaniques et chimiques des superalliages qui les constituent. Plus précisément, l’objectif de cette thèse est, dans un premier temps, d’améliorer les alliages utilisés pour le fibrage à 1000°C, puis dans un second temps, de trouver un superalliage pouvant fibrer à 1125°C. Ces travaux ont été menés sur deux familles de superalliages : base nickel et base cobalt. Les propriétés chimiques ont été caractérisées par des essais thermogravimétriques et les propriétés mécaniques par des essais de fluage flexion 3 points. Pour l’alliage base Ni, l’influence des éléments minoritaires subis, Mn et Si, a été étudiée. Les propriétés mécaniques de cet alliage ont fait, ensuite, l’objet d’essais d’amélioration par l’addition de titane, zirconium, tantale, hafnium et de niobium. L’addition d’aluminium a été aussi expérimentée mais ayant pour but d’améliorer les propriétés chimiques de l’alliage. Enfin, des études ont été aussi menées sur l’addition de métaux nobles (Pd et Ru) et de terres rares (Y, La et Ce). Concernant les superalliages base cobalt, l’étude s’est portée sur un alliage base Co qui a antérieurement montré de bonnes propriétés générales pour une utilisation à 1125°C et non à 1000°C. Des variantes avec une teneur abaissée en tantale, sans hafnium et sans tungstène ont été étudiées. Pour clore ces travaux, l’augmentation de la teneur en nickel et un traitement thermique ont été étudiés afin d’améliorer la résistance à l’oxydation de ce second alliageThe fiberizing spinners used to produce the glass fibers undergo sizable mechanical, chemical and thermal solicitations. Therefore, this piece is degraded and must be periodically replaced. The purpose of these works is to increase the lifetime of the fiberizing spinners by improving the mechanical and chemical properties of the superalloys that constitute them. More precisely, the objective of this thesis is, in the first time, to improve the alloys used to fiberize at 1000°C, and in a second time, to find a superalloy that can fiberize at 1125°C. These works are focused on two families of superalloys: nickel-based and cobalt-based. The chemical properties are characterized by the thermogravimetry tests and the mechanical properties by 3 points flexural creep tests. For the Ni-based alloy, the influences of unwanted minority elements, Mn and Si, were studied. The mechanical properties of this alloy are subject to improvement tests by the addition titanium, zirconium, tantalum, hafnium and niobium. The aluminium addition was also experimented but with the aim of improving the chemical properties of the alloy. Finally, the studies were also driven on the addition of noble metals (Pd and Ru) and of rare earths (Y, La and Ce). Concerning the cobalt-based superalloys, the study focused on an alloy which has previously shown good general properties to be used at 1125°C and no at 1000°C. The versius with a lowered content in tantalum, without tungsten and without hafnium were studied. To close this work, the increase of nickel and a heat treatment were studied in order to improve the oxidation resistance of this second alloy
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Ur-Rehman, Hamad [Verfasser], Mathias [Gutachter] Göken, and Uwe [Gutachter] Glatzel. "Solid Solution Strengthening and Diffusion in Nickel- and Cobalt-based Superalloys / Hamad Ur-Rehman. Gutachter: Mathias Göken ; Uwe Glatzel." Erlangen : FAU University Press, 2016. http://d-nb.info/1112737502/34.
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[Verfasser], Hamad ur Rehman, Mathias [Gutachter] Göken, and Uwe [Gutachter] Glatzel. "Solid Solution Strengthening and Diffusion in Nickel- and Cobalt-based Superalloys / Hamad Ur-Rehman. Gutachter: Mathias Göken ; Uwe Glatzel." Erlangen : FAU University Press, 2016. http://nbn-resolving.de/urn:nbn:de:bvb:29-opus4-74073.
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