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1
Clark, A. C. "Forging of nickel-base superalloys." Thesis, Swansea University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636261.
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The properties of the nickel based superalloy Inconel 718 (IN 718) are insufficient for its use in the higher temperature stages at the rear of the gas turbine jet engine compressor. Considerable effort is being made to adapt the microstructure and improve the properties by thermomechanical processing, to enable the cheaper IN 718 alloy to replace the current alloy, Waspaloy, in the fabrications of these rear-end compressor disks. The initial casting of the alloy leads to an unsuitably coarse microstructure. The alloy is therefore forged in order to optimise the microstructure and hence mechanical properties. Isothermal compression tests were carried out on the alloy in the as-cast condition to investigate both dynamic and static microstructural events between 900°C and 1121°C. Strain rates ranged from 0.001s-1 to 10.0s-1 with strains from 0.1 to 0.6. Microstructural investigations revealed that complete dynamic recrystallisation was not evident in any of the samples, however partial recrystallisation occurred in samples forged at the higher temperatures and strain rates. The amount of dynamic recrystallation was found to increase primarily with temperature but also with strain rate. Complete static recrystallation was found to have occurred in tests conducted with a post-forge hold time at temperature. The degree of this recrystallisation and the resulting grain size were found to depend primarily on temperature and strain and less so on strain rate. Stress levels varied systematically with temperature and strain rates. Higher stress levels resulted from lower testing temperatures and higher strain rates. Currently property data of material in the as-cast condition is not widely available. Constitutive analysis was performed on the Stress-strain data for subsequent implementation in the forging simulation program "BILLIE". These results would then be used to provide simulations of the industrial Inco Alloys forging process.
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Zou, Xiaodong. "Impedance spectroscopy of nickel base superalloys." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/20307.
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Karunaratne, Mudith Sakalawalli Acharige. "Diffusional phenomena in nickel-base superalloys." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621097.
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Li, Ting. "Banding in nickel-base superalloys and steels." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/344.
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Process irregularities in remelting furnace operation have an impact on the ingot solidification structure which depends on the local thermal conditions and the alloy concerned. In this work, a laboratory investigation into the structures resulting from interruptions in solid growth is presented in order to understand the cause and effect relationship between the solidification interruption and banding. The results demonstrate the range of structure, segregation and precipitation changes which are experienced by a range of alloys including Inconel 718, Nimonic 80A, Waspaloy andM50. In the case of alloys which form primary precipitates, the interruption period is shown to give rise to structure changes. Segregations are found due to the interruption. We also comment on the differences observed between industrial examples of banding and the laboratory samples which may be due to the absence of liquid movement in the latter technique. It is concluded that the interruption in solidification condition during a directionally solidification itself can produce banding through its effects on the morphology of precipitates.
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Reynolds, Gary James. "Damage rate approaches for nickel-base superalloys." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/18863.
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Allan, Christine Dianne. "Plasticity of nickel base single crystal superalloys." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11771.
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Miller, Mark. "Fatigue life prediction of nickel base superalloys." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/68693/.
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Neural networks have been used extensively in material science with varying success. It has been demonstrated that they can be very effective at predicting mechanical properties such as yield strength and ultimate tensile strength. These networks require large amounts of input data in order to learn the correct data trends. A neural network modelling process has been developed which includes data collection methodology and subsequent filtering techniques in conjunction with training of a neural network model. It has been shown that by using certain techniques to ‘improve’ the input data a network will not only fit seen and unseen Ultimate Tensile Strength (UTS) and Yield Strength (YS) data but correctly predict trends consistent with metallurgical understanding. Using the methods developed with the UTS and YS models, a Low Cycle Fatigue (LCF) life model has been developed with promising initial results. Crack initiation at high temperatures has been studied in CMSX4 in both air and vacuum environments, to elucidate the effect of oxidation on the notch fatigue initiation process. In air, crack initiation occurred at sub-surface interdendritic pores in all cases. The sub-surface crack grows initially under vacuum conditions, before breaking out to the top surface. Lifetime is then dependent on initiating pore size and distance from the notch root surface. In vacuum conditions, crack initiation has been observed more consistently from surface or close-to-surface pores - indicating that surface oxidation is in-filling/”healing” surface pores or providing significant local stress transfer to shift initiation to sub-surface pores. Complementary work has been carried out using PWA 1484 and Rene N5. Extensive data has been collected on initiating pores for all 3 alloys. A model has been developed to predict fatigue life based upon geometrical information from the initiating pores. A Paris law approach is used in conjunction with long crack propagation data. The model shows a good fit with experimental data and further improvements have been recommended in order to increase the capability of the model.
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Lambert, David. "Fatigue damage accumulation in nickel base superalloys." Thesis, University of Sheffield, 1994. http://etheses.whiterose.ac.uk/15129/.
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Tangentially oriented Waspaloy specimens taken from the bore section of a turbine disc were subjected to low cycle fatigue in the form of cyclic four point bend tests. Substantial differences in grain size and structure occurred across the section of the disc. Fatigue damage occurred primarily as a result of persistent slip band formation, cell formation, Orowan looping and precipitate shearing. A small number of grains exhibited dislocation cells, normally associated with higher stacking fault energy materials. The number and width of persistent slip bands increased with the number of cycles, but varied both between grains and stress levels. It is proposed that initially looped precipitates were subsequently sheared. Crack initiation was observed as early as 1/12 of fatigue lifetime, predominantly from inclusions. A stage-I/stage-II crack propagation transition occurred at approximate 4Kl values of 30MPa.m1/ 2 , when the plastic zone size was comparable to the material grain size. Results imply that short crack growth requires prior slip band formation.
9
Arnold, K. "High temperature oxidation behaviour of nickel-base superalloys." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3005778/.
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The Ni-base superalloys are a popular range of materials for study following consolidation by additive manufacturing (AM) techniques, such as selective laser melting (SLM). However, very little work has been done to assess the high temperature oxidation behaviour of Ni-base superalloys fabricated by SLM, despite the fact that this class of alloy is designed primarily for operation at temperatures >650°C. In the present work, the isothermal oxidation behaviour of the Ni-base superalloys Alloy 718 and Alloy 625 was studied following consolidation by SLM. A third Ni-base superalloy, Haynes 230, which is doped with a small amount of the reactive element La, was also studied following SLM-consolidation. The same three alloys were studied in wrought form for comparison purposes. Also studied following consolidation by SLM were oxide dispersion strengthened (ODS) derivatives of Alloy 625 and Haynes 230, which contained a 0.5 Wt. % addition of Y2O3, added by mechanical alloying (MA), and developed during the project for which the present work was conducted. Comparators for the ODS variants of Alloy 625 and Haynes 230 were fabricated by spark plasma sintering (SPS). All of the alloys were oxidised in laboratory air at 900°C and the oxidation kinetics determined using thermogravimetric analysis (TGA), or from scale thickness measurements. The work has shown that SLM-consolidated Alloy 718 oxidised slightly faster than wrought Alloy 718. SLM-consolidated Haynes 230 oxidised ~3x faster than wrought Haynes 230 alloy, but SLM-consolidated Alloy 625 oxidised ~2x slower than wrought Alloy 625. The ODS variant of Alloy 625, in SLM-consolidated and SPS-consolidated forms, oxidised ~10x more slowly than wrought Alloy 625. The SLM-consolidated ODS variant of Haynes 230 oxidised at approximately the same rate as wrought Haynes 230, but in SPS-consolidated form the ODS variant of Haynes 230 oxidised ~10x faster than wrought Haynes 230. The improvement in the oxidation resistance of the ODS variant of Alloy 625 is attributed to the well-known reactive element effect, which occurs when alloys are appropriately doped with reactive elements. The reduction in the oxidation resistance of the SPS-consolidated ODS variant of Haynes 230 is attributed to overdoping of the alloy with reactive elements, which is known to decrease the oxidation resistance of nickel-base alloys. It is proposed that SLM-consolidation improves the oxidation resistance of the ODS variant of Haynes 230 by ‘slagging off’ reactive elements from the alloy during consolidation, but for the same reason, the oxidation resistance of Haynes 230 is reduced by SLM-consolidation.
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Marchand, Norman J. "Thermal-mechanical fatigue behavior of nickel-base superalloys." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/31003.
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Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE
Bibliography: leaves 185-199.
by Norman J. Marchand.
Sc.D.
11
Wagner, Axel. "Texture development in nickel base superalloys during directional solidification." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269982.
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Sekhar, Nettem Chandra. "Characterisation of power beam welds in nickel-base superalloys." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442490.
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Kouichi, Murakami. "Directional recrystallisation in mechanically alloyed ODS nickel base superalloys." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319573.
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Wilson, Alison Sarah. "Stability of nickel-base superalloys for turbine disc applications." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/279061.
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Requirements for increased operating efficiencies mean that future generations of aero-engines will need to operate at temperatures beyond the capabilities of current nickel-base superalloys. As a result, new alloy compositions for turbine disc applications are being developed. Optimising these alloy compositions requires balancing directly competing requirements. Increased Cr contents are needed to provide environmental resistance and increased concentrations of other refractory metals to improve solid solution strengthening. However, these elements compromise the alloyâs long-term microstructural stability by promoting the formation of topologically close-packed (TCP) phases, which are deleterious to alloy performance. High $\gamma^\prime$ volume fractions, which are needed to provide high-temperature strength, exacerbate the problem by increasing the concentration of these elements in the $\gamma$ phase. Therefore, an understanding of TCP formation and the compositional limits of stability is vital in the design of new alloys. This thesis presents a combination of fundamental studies of TCP phase formation in model alloys and microstructural assessment of the thermal stability of developmental alloy compositions. Knowledge of the effect of individual elements on thermal stability is important to enable the development of optimised alloy compositions. As a result, the first fundamental study investigated the effect of Co content on thermal stability. An unexpected transition in $\sigma$ precipitation behaviour after 500 hours at 800°C was observed between 12 and 16 at.\% Co. It is proposed that this behaviour may be due to the effect of Co on the $\gamma$/$\gamma^\prime$ partitioning behaviour of other elements. Preliminary results from further fundamental studies investigating the effect of the Mo/W ratio and B content on thermal stability are also presented. Decreasing the Mo/W ratio was found to reduce the quantity of $\sigma$ precipitation and promote the precipitation of a W-rich phase. B additions were found to promote the precipitation of the M$_3$B$_2$ phase. Thermodynamic predictions are frequently used to inform alloy design as an alternative to time-consuming and costly experiments. However, the accuracy of solvus temperature predictions for TCP phases has not been thoroughly considered. In this work, it was found that differential scanning calorimetry could be used as a means of measuring $\sigma$ solvus temperature in a series of alloys designed to be sufficiently unstable with respect to $\sigma$ precipitation. Comparison of experimental results with thermodynamic solvus temperature predictions revealed a significant underprediction of the $\sigma$ solvus temperatures for all of the studied alloys. This can inform our use of such predictions during alloy design. The ability to quantify the amount of TCP precipitation that occurs is extremely important when assessing the thermal stability of alloys. A new method was applied to the problem of TCP quantification, involving synchrotron X-ray diffraction of solid aged samples. This was an attempt to avoid some of the problems identified with the commonly used quantification method, which involves electrolytic extraction of minor phases, and assess the accuracy of the results produced by this method. Samples of a currently used commercial alloy, RR1000, were investigated following ageing for up to 5000 hours at 800°C, revealing the evolution of phases at this temperature. The presence of extremely low quantities of minor phases was successfully detected in the solid samples using this method. However, these quantities were too low for this to be a reliable method of quantification for commercial alloys. In parallel with these fundamental and technique-based studies, the thermal stability of a number of candidate alloys, which were developed during the design of a next-generation disc alloy by Rolls-Royce, was assessed. The alloys were characterised following a variety of thermal exposure temperatures and durations, which were determined by industrial needs at the time. Various minor phases were identified depending on the alloy compositions, including the TCP phases, $\sigma$ and $\mu$, as well as MC and M$_{23}$C$_6$ carbides and M$_3$B$_2$ borides.
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Vorontsov, Vassili Andreyevich. "Phase field modelling of dislocations in nickel base superalloys." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610288.
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Ghasemi, Hamid-Reza M. R. "Computer simulation of carburization corrosion of nickel-base superalloys." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/76035.
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A computer model for diffusion-controlled internal precipitation was used to simulate the corrosion behavior of Ni-based superalloys in carburizing atmospheres. The model is based on Crank-Nicholson finite difference solution of the diffusion equation. The code also includes the ternary cross diffusion effect due to substitutional alloying elements that are preferentially oxidized. The model can treat two sets of boundary conditions corresponding to the presence or absence of a protective oxide scale. It accounts for internal precipitation of corrosion products whenever thermodynamic solubility limits are exceeded. Up to four different carbides can be treated simultaneously. The solubility product is computed for each reaction and the amount of carbon that reacts is removed from the diffusion process. Under non-protective conditions, the predictions of model were compared to carburization profiles obtained experimentally in H₂-CH₄ environment tests. Results are presented for the formation of Cr, Mo, Ti, W, and Nb carbides in Ni-based superalloys. The predicted corrosion profiles are in qualitative agreement with experimental data.Master of Science
17
Song, Hyo-Jin. "Microstructural Evolution and Deformation Mechanisms in Nickel-Base SuperAlloys." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1282059574.
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Schweitzer, Luiz Guilherme de Souza. "Laser cladding for epitaxial nickel base superalloys turbine blades." reponame:Repositório Institucional da UFSC, 2014. https://repositorio.ufsc.br/xmlui/handle/123456789/129625.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2014.Made available in DSpace on 2015-02-05T21:18:49Z (GMT). No. of bitstreams: 1 328410.pdf: 5168954 bytes, checksum: a55c798d806d29cc35e63be5e11587fe (MD5) Previous issue date: 2014
A prosperidade e larga utilização da aviação como meio de transporte civil, nacional e internacional, exige seriedade no condicionamento das aeronaves. A manutenção preventiva é um ponto fundamental para que sejam evitados desastres aéreos. A verificação dos motores é indispensável e, devido ao alto valor agregado, corresponde aos custos mais elevados de recondicionamento. As turbinas, por estarem sujeitas a elevada temperatura e pressão, geralmente apresentam o maior número de componentes danificados. Por esta razão há o interesse no desenvolvimento de técnicas para o reparo eficaz de pás de turbina. Erosão e formação de trincas são danos comuns que necessitam de recondicionamento. A recente aplicação de pás monocristalinas (SX), no lugar de policristalinas, apresenta vantagens por suportar melhor as elevadas temperaturas e com isto aumentar a eficiência dos motores [1, 2]. No entanto, não há um método reconhecido para o reparo das pás monocristalinas. A proposta deste trabalho consiste na aplicação de laser cladding com injeção de pó, devido a características como o tratamento localizado e controle de material fornecido. Este processo é apropriado devido principalmente à flexibilidade e baixo nível de diluição. Foram desenvolvidos dois métodos para promover o reparo de tais defeitos. Um método consiste na remoção completa de camadas de material onde estão situadas as trincas. O outro prevê a remoção de apenas um pequeno volume da estrutura afetada, através de um entalhe que retira o volume danificado. Com isto, a perda de material, o tempo de trabalho e os custos de manutenção podem ser drasticamente reduzidos. O entalhe tem de ser soldável e também permitir a solidificação de material no mesmo plano orientado como a microestrutura inicial. Para isto, um gradiente de temperatura deve ser introduzido a fim de orientar o crescimento de grão. No entanto, existem desafios para alcançar uma estrutura de cristal único sem rachaduras e poros, devido à distribuição de energia no interior do entalhe. Progressos atingidos e novos desafios são apresentados neste trabalho.
Abstract : The prosperity and widespread use of aviation as a civil national and international transport requires seriousness in the aircraft conditioning. Preventive maintenance is the key to avoid disasters. For that, is essential the check of engines, which corresponds to the higher reconditioning costs. The turbines, due to elevated temperature and pressure, usually have the highest number of damaged parts. For this reason, there is an interest in developing techniques for the efficient repair of turbine blades. Erosion and crack formation are common damages that require refurbishing. The recent application of single crystal (SX) turbine blades, instead of polycrystalline, present better withstands in high temperatures and thus increases the efficiency of the engines [1, 2]. However, a recognized method for the repair of SX turbine blades has to be developed. The proposal of this work involves the application of laser cladding with powder injection, due to characteristics such as localized treatment and control of the material injected. This process is particularly suitable due to flexibility and low dilution levels. There are two techniques developed to promote the repair of such defects. One way is by the removal of complete layers in which the cracks are located. Another possibility is to remove just a small volume of the affected microstructure. Therewith the loss of material and working time may be drastically reduced as well as the maintenance costs. The notch must be weldable and permit the material solidification in the same oriented plane as the original structure. For that, a temperature gradient has to be introduced in order to guide the grain growth. However, there are challenges to achieve a SX structure without cracks and pores due to energy distribution inside the notch. Current achievements and further challenges are presented in this work.
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Jackson, Martin Peter. "Modelling and characterisation of phase transformations in nickel-base superalloys." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435368.
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Kong, Chau Nyen. "High temperature mechanical behaviour of single crystal nickel base superalloys." Thesis, University of Bristol, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.480694.
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Fernandez-Zelaia, Patxi. "Thermomechanical fatigue crack formation in nickel-base superalloys at notches." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/48991.
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Hot sections of gas engine turbines require specialized materials to withstand extreme conditions present during engine operation. Nickel-base superalloys are typically used as blades and disks in the high pressure turbine section because they possess excellent fatigue strength, creep strength and corrosion resistance at elevated temperatures. Components undergo thermomechanical fatigue conditions as a result of transient engine operation. Sharp geometric features, such as cooling holes in blades or fir-tree connections in disks, act as local stress raisers. The material surrounding these features are potential sites of localized inelastic deformation and crack formation. To reduce customer costs associated with unnecessary overhauls or engine down-time, gas turbine manufacturers require accurate prediction methods to determine component endurances. The influence of stress concentration severity on thermomechanical fatigue crack formation is of particular importance as cracks often initiate in these hot spots. Circumferentially notched specimens were utilized to perform thermomechanical fatigue experiments on blade material CM247LC DS and disk material PM IN100. A parametric study on CM247LC DS was performed utilizing four notched specimens. Experimental results were coupled with finite element simulations utilizing continuum based constitutive models. The effects of applied boundary conditions on crack initiation life was studied in both alloys by performing experiments under remotely applied force and displacement boundary conditions. Finite element results were utilized to develop a life prediction method for notched components under thermomechanical fatigue conditions.
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Wang, Billie. "Integrated Computational Microstructure Engineering for Single-Crystal Nickel-base Superalloys." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1228147112.
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Singh, Antariksh Rao Pratap. "Mechanisms of Ordered Gamma Prime Precipitation in Nickel Base Superalloys." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc67949/.
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Commercial superalloys like Rene88DT are used in high temperature applications like turbine disk in aircraft jet engines due to their excellent high temperature properties, including strength, ductility, improved fracture toughness, fatigue resistance, enhanced creep and oxidation resistance. Typically this alloy's microstructure has L12-ordered precipitates dispersed in disordered face-centered cubic γ matrix. A typical industrially relevant heat-treatment often leads to the formation of multiple size ranges of γ¢ precipitates presumably arising from multiple nucleation bursts during the continuous cooling process. The morphology and distribution of these γ′ precipitates inside γ matrix influences the mechanical properties of these materials. Therefore, the study of thermodynamic and kinetic factors influencing the evolution of these precipitates and subsequent effects is both relevant for commercial applications as well as for a fundamental understanding of the underlying phase transformations. The present research is primarily focused on understanding the mechanism of formation of different generations of γ′ precipitates during continuous cooling by coupling scanning electron microscopy (SEM), energy filtered TEM and atom probe tomography (APT). In addition, the phase transformations leading to nucleation of γ′ phase has been a topic of controversy for decades. The present work, for the first time, gives a novel insight into the mechanism of order-disorder transformations and associated phase separation processes at atomistic length scales, by coupling high angle annular dark field (HAADF) - STEM imaging and APT. The results indicate that multiple competing mechanisms can operate during a single continuous cooling process leading to different generations of γ′ including a non-classical mechanism, operative at large undercoolings.
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Busse, Christian. "Aspects of Crack Growth in Single-Crystal Nickel-Base Superalloys." Licentiate thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-143058.
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This Licentiate of Engineering thesis is a product of the results generated in the research project KME-702, which comprises modelling, microstructure investigations and material testing of cast nickel-base superalloys. The main objective of this work is to model the fatigue crack propagation behaviour in single-crystal nickel-base superalloys. To achieve this, the influence of the crystal orientations on the cracking behaviour is assessed. The results show that the crystal orientation is strongly affecting the material response and must be accounted for. Furthermore, a linear elastic crack driving force parameter suitable for describing crystallographic cracking has been developed. This parameter is based on resolved anisotropic stress intensity factors and is able to predict the correct crystallographic cracking plane after a transition from a Mode I crack. Finally, a method to account for inelastic deformations in a linear elastic fracture mechanics context was investigated. A residual stress field is extracted from an uncracked finite-element model with a perfectly plastic material model and superimposed on the stress field from the cracked model with a linear elastic material model to account for the inelastic deformations during the determination of the crack driving force. The modelling work is validated by material testing on two different specimen geometries at different temperatures. This Licentiate of Engineering thesis consists of two parts, where Part I gives an introduction and background to the research area, while Part II consists of three papers.Denna licentiatavhandling är en produkt av resultat som genererats i forskningsprojektet KME-702, och omfattar modellering, mikrostrukturundersökningar och materialprovning av gjutna nickelbaserade superlegeringar. Huvudsyftet med detta arbete är att modellera sprickförloppet under utmattning i enkristallina nickelbaserade superlegeringar. För att uppnå detta har kristallorienteringens inverkan på sprickbeteendet utvärderats. Resultaten visar att kristallorienteringen har en stark inverkan på materialbeteendet, således måste hänsyn till denna tas. Dessutom har en linjär-elastisk sprickdrivkraftsparameter lämplig att beskriva kristallografisk sprickbildning utvecklats. Denna parameter är baserad på anisotropa spänningsintensitetsfaktorer på kristallplan och kan prediktera det korrekta kristallografiska sprickplanet efter övergång från Modus I spricka. Slutligen har undersökts en metod för att ta hand om inelastiska deformationer i en linjär-elastisk brottmekanikskontext. Ett restspänningsfält extraherades från en osprucken finita element modell med en ideal plastisk materialmodell. Denna överlagrades på spänningsfältet från den spruckna modellen, som analyserades med en linjär-elastisk materialmodell, för att ta hänsyn till de inelastiska deformationerna vid bestämning av sprickdrivkraften. Modelleringsarbetet validerades genom materialprovning på två olika provgeometrier vid olika temperaturer. Licentiatavhandlingen består av två delar, där del I ger en introduktion och bakgrund till forskningsområdet medan del II består av tre papper.
Dieses Lizentiat der Ingenieurwissenschaften ist im Rahmen des Forschungsprojekts KME-702 entstanden, welches Modellierung, Mikrostrukturuntersuchungen und Materialtests von gegossenen nickelbasierten Superlegierungen umfasst. Das Hauptziel dieser Arbeit ist die Modellierung der Ermüdungsrissausbreitung in einkristallinen nickelbasierten Superlegierungen. Um dieses zu erreichen, wurde der Einfluss der Kristallorientierungen auf das Rissverhalten untersucht. Die Ergebnisse zeigen, dass die Kristallorientierung das Materialverhalten stark beeinflusst und daher berücksichtigt werden muss. Darüber hinaus wurde ein linear elastischer Rissantriebskraftparameter entwickelt, der zum Beschreiben von kristallographischen Rissen geeignet ist. Dieser Parameter basiert auf aufgelösten anisotropen Spannungsintensitätsfaktoren und ist in der Lage, die korrekte kristallographische Rissebene nach einem Übergang von einem Modus I Riss vorherzusagen. Abschließend wird in einem linear-elastisch bruchmechanischen Kontext eine Methode untersucht, die nichtelastischen Deformationen bei der Bestimmung der Rissantriebskraft zu berücksichtigen. Dazu wird aus einem Finite-Elemente Modell, welches keinen Riss aufweist und mit einem perfekt plastischen Materialmodell beschrieben wird, das Restspannungsfeld extrahiert und dem Spannungsfeld überlagert, welches aus dem Modell mit Riss unter Verwendung eines linear elastischen Materialmodells erzeugt wurde. Die Modellierung wird durch Materialtests an zwei verschiedenen Probengeometrien bei unterschiedlichen Temperaturen validiert. Dieses Lizentiat der Ingenieurwissenschaften besteht aus zwei Teilen, wobei Teil I eine Einführung und einen Hintergrund in das Forschungsgebiet gibt, während Teil II aus drei Forschungsartikeln besteht.
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Aba-Perea, Pierre-Emmanuel. "In-situ stress relaxation studies in nickel-base superalloy forgings." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/insitu-stress-relaxation-studies-in-nickelbase-superalloy-forgings(13c9a3e7-8ad3-4d9f-abb3-4e379745318a).html.
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The manufacturing of nickel-base superalloy forging for aero-engine applications requires a number of thermo-mechanical processing steps, which generate significant residual stresses that can result in distortion, uncontrolled deformation of the component during machining, or, when added to the in-service stresses, they will increase the crack initiation probability and hence reduce component life. Ageing treatments are applied to nickel-base superalloys in order to precipitate the strengthening phases that give to the alloys their remarkable strength over a wide temperature range. These isothermal treatments also result in a reduction of the residual stress level by means of thermal stress relaxation. In this work, the focus has been on the study of the thermal residual stress relaxation induced by the ageing treatment of wrought nickel-base superalloys. The aim of this work is to improve the understanding of the residual stress relaxation process and the different deformation mechanisms involved in the stress relaxation during isothermal treatments. This has been achieved by combining neutron diffraction with a new in-situ heating setup in order to track the elastic strain evolution in the centre of quenched disc shaped forgings of Inconel 718 and Udimet 720LI. This research has resulted in the implementation of an induction heating setup which was designed in order to serve in-situ residual stress analysis during isothermal treatments of large components at temperatures up to 1000°C. The in-situ analysis of residual stresses required the development of a standardised method which consists of monitoring the d-spacing evolution in stressed samples and in stress-free samples during isothermal treatments in order to determine the time dependent stress evolution. Stress calculations were performed using temperature dependent diffraction elastic constants which were determined experimentally for Inconel 718 and Udimet 720LI at high temperatures. The in-situ neutron diffraction measurements in water quenched disc shaped forgings of Inconel 718 of different thickness during isothermal treatments at 720°C revealed that the stress relaxation amplitude does not vary significantly with the initial stress distribution. However, the stress relaxation rate is strongly affected by the annealing temperature as stress relaxation through creep was observed to evolve at a diminishing rate during the isothermal treatment of Inconel 718 at 720°C and 750°C while no further stress relaxation occurred at 650°C. Most of the stress relaxation was found to occur during the heating stage as a result of a combination of plasticity and early stage creep relaxation. In-situ and ex-situ measurements exhibited good agreement on the amplitude of residual stress relaxation. It was found that a heat treatment at 750°C for 8h reduced the stresses by approximately 70% in Inconel 718 and only 20% in Udimet 720LI. For all in-situ experiments it was possible to fit the stress relaxation data by using logarithmic functions, which can now be used for validating and/or improving process models.
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Bande, Gilbert. "A combined approach for analysis of single crystal nickel base superalloys /." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37868.
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The purpose of this research is to develop a new tool for mechanical design and analysis of single crystal (SC) nickel base superalloys used in gas turbine engine components. The principle of this tool is based on the extension of the predictive models for isotropic material behavior to anisotropic materials such as SC nickel, base superalloys. This objective is achieved by combining the two main approaches used in the literature for SC materials development: the macroscopic approach and the microscopic approach. For that reason, this theory is designated as the "combined approach " (CA).The structure of the CA theory requires two main elements: a viscoplastic model (that admits a yield function) and a slip factor. The viscoplastic model describes the behavior of the material in the macroscopic level. Conversely, the slip factor based on the crystallographic theory, accounts for the micro-slip state that dominates SC materials during deformation.
In order to determine the slip factor, a preliminary slip trace study of the crystal is established. Also to determine material constants from experimental data, a procedure has been developed to reduce the 3D basic equations into a one-dimensional form. The model has been evaluated for its predictive capability on SC material behavior including orientation dependence of the initial yielding, tension/compression asymmetry, stress-strain response, fully reversed cyclic response, creep response and relaxation response. In almost all the cases, good correlation has been observed between the predicted responses and experimental data, when available. Furthermore, it is believable that the CA can be successfully used for many other SC materials such as the body-centered-cubic (b.c.c) or the hexagonal-closed-packet (h.c.p). In view of all these results, the CA theory seems to offer the greatest promise in this regard. Limitations and future development needs are discussed.
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Cox, D. C. "Characterisation of the microstructural evolution of single crystal nickel-base superalloys." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598094.
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The work contained in this thesis is devoted to the study of microstructural evolution of nickel-based superalloy single crystals. The main issues addressed, are improved understanding of the mechanisms of microstructural evolution with regard to; (i) processing variables; (ii) the effect of in-service conditions. The majority of the work concentrates on the second-generation single crystal nickel-base superalloy CMSX-4. Data is gathered and analysed from a series of experiments studying different aspects of microstructural evolution. Throughout the work extensive use is made of metallographic and microscopical techniques. The first experimental part of this work (Chapter 3) investigates the solidification behaviour and elemental microsegregation contained in single crystal castings. Dendrite arm spacing, microsegregation and solidification range are studied and compared in three different single crystal superalloys, SRR99, CMSX-4 and RR3000. Chapter 4 studies the sensitivity of a nickel-base superalloy, CMSX-4, to recrystallisation. This phenomenon occurs as a result of castings undergoing plastic strain in the mold during solidification and cooling. The subsequent homogenisation heat-treatment that cast single crystals must undergo in order to reduce dendritic microsegregation then results in the casting recrystallising. This work establishes critical strain and temperature values necessary for recrystallisation to occur following the introduction of plastic strain at both room and elevated temperature. Chapter 5 studies the effects of age heat-treatment on the creep rupture behaviour of CMSX-4 at three different stress and temperature regimes. Different γ\γ', microstructures have been developed via modified age heat-treatments, and it is the effects of these modifications on the creep rupture behaviour that are investigated. The study uses mainly scanning electron microscopy to investigate the effects and evolution of the microstructure during the creep tests, and the creep behaviour is rationalised in terms of the developed microstructures.
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Hadjiapostolidou, Despina. "Temporal behaviour of nickel-base superalloys Rene 80 and CMSX-4." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509793.
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REZENDE, TATHIANA CARNEIRO DE. "GAMMA PRIME CHARACTERIZATION IN NICKEL BASE SUPERALLOYS THROUGH DIGITAL IMAGE ANALYSIS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=6232@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROEste trabalho consiste na caracterização da fase gama linha em superligas de níquel através do processamento e análise digital de imagens. Amostras de uma superliga de níquel foram submetidas a 10 tratamentos térmicos diferentes. Após o tratamento térmico, estas amostras foram preparadas para avaliação metalográfica e imagens da microestrutura foram adquiridas no microscópio eletrônico de varredura (MEV). A fase gama linha presente no material foi segmentada e posteriormente medida através do processamento digital de imagens. Foram analisadas 429 imagens, o que gerou medidas de mais de 225,000 partículas. Foi medida a fração de área ocupada pelas partículas de gama linha, a quantidade de partículas por imagem, a área de cada partícula e a razão de aspectos das partículas. Uma análise estatística dos resultados foi realizada. Os resultados mostraram menor concentração e maior tamanho de gama linha com o aumento da temperatura, conforme era esperado. O uso de análise digital de imagens permitiu obter medidas com altíssima confiabilidade, uma vez que a alta velocidade de análise permite uma amostragem muito superior às técnicas tradicionais de caracterização microestrutural.
This study consists of the characterization of the gamma prime phase in nickel base superalloys using digital image processing and analysis. Samples of a nickel base superalloy were heat treated to 10 different temperatures. After the heat treatment cycle, the samples were prepared for metallographic evaluation and images of the microstructure were acquired using a scanning electron microscope (SEM). The gamma prime was segmented and measured using digital image processing methods. 429 images were analyzed, in which over 225000 particles were measured. The following parameters were obtained: area fraction of gamma prime, number of particles of gamma prime per image, area of each particle and the particles' feret ratio. An statistical analysis of the data was performed The results showed that the gamma prime fraction decreases and its size increases with temperature increase, as expected. The use of digital image analysis provided measurements with high accuracy, as the high speed of digital image analysis allowed sampling much superior to the traditional microstructural characterization methods.
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Mignanelli, Paul Michael. "The design of new nickel-base superalloys with high niobium contents." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709110.
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Sung, Pil Kyung 1961. "Equilibrium partition ratios, densities, and transport phenomena in nickel-base superalloys." Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282823.
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To simulate transport phenomena, macrosegregation and segregation defects known as "freckles" during directional solidification of Ni-base superalloys, numerical modeling can be used; hence it is essential to have reasonably accurate values of the thermodynamic and transport properties for the alloys. In this research, therefore, the equilibrium partition ratios of the solutes in the Ni-Al-Ta-Cr quaternary system, as a model alloy, were measured, and the solid- and liquid-densities in Ni-base superalloys. were estimated. Also, the importance of these properties on the sensitivity of the results of numerical simulations was studied. The partition ratios apply to equilibria between melts and gamma-phase in the range of 1615 K to 1694 K, and it was found that the equilibrium partition ratio of Ta varies from approximately 0.6 at dilute Ta to 0.85 at 17 wt.% Ta. For the same range of Ta-contents, the partition ratios of Al and Cr vary much less and range from about 0.92 to 0.96. In addition to the partition ratios, the liquidus temperatures of the liquid in equilibrium with γ in the Ni-Al-Ta-Cr system were estimated with a multidimensional regression analysis. To calculate the densities of solid Ni-base superalloys as functions of temperature and composition, lattice parameters at 20°C and coefficients of thermal expansion (CTEs) were estimated by combining available data. The CTEs calculated from the regressions result in densities that are within 0.5% error or less for seventeen alloys. To estimate the densities of liquid Ni-base superalloys, the densities and temperature coefficients of density of the liquid transition-metals, which are used as alloy elements in Ni-base superalloys, were applied to a simple correlation. By using this approach, the estimates of the liquid densities of five Ni-base superalloys agree with the measured values to ±2.5%. Finally, the importance of using reasonably accurate estimates of the transport properties was illustrated by simulations of the thermosolutal convection and macrosegregation during solidification in a directionally solidified Ni-base alloy casting. In these simulations, the sensitivities of equilibrium partition ratio, solutal expansion coefficient and viscosity on the simulation of macrosegregation were determined. It was found that the segregation and convection are sensitive to the properties, especially to the equilibrium partition ratio.
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Song, Jin E. "Hierarchical multiscale modeling of Ni-base superalloys." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34855.
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Ni-base superalloys are widely used in hot sections of gas turbine engines due to the high resistance to fatigue and creep at elevated temperatures. Due to the demands for improved performance and efficiency in applications of the superalloys, new and improved higher temperature alloy systems are being developed. Constitutive relations for these materials need to be formulated accordingly to predict behavior of cracks at notches in components under cyclic loading with peak dwell periods representative of gas turbine engine disk materials. Since properties are affected by microstructure at various length scales ranging from 10 nm tertiary γ' precipitates to 5-30 μm grains, hierarchical multiscale modeling is essential to address behavior at the component level.
The goal of this work is to develop a framework for hierarchical multiscale modeling network that features linkage of several fine scale models to incorporate relevant microstructure attributes into the framework to improve the predictability of the constitutive model. This hierarchy of models is being developed in a collaborative research program with the Ohio State University. The fine scale models include the phase field model which addresses dislocation dissociation in the γ matrix and γ' precipitate phases, and the critical stresses from the model are used as inputs to a grain scale crystal plasticity model in a bottom-up fashion. The crystal plasticity model incorporates microstructure attributes by homogenization.
A major task of the present work is to link the crystal plasticity model, informed by the phase field model, to the macroscale model and calibrate models in a top-down fashion to experimental data for a range of microstructures of the improved alloy system by implementing a hierarchical optimization scheme with a parameter clustering strategy. Another key part of the strategy to be developed in this thesis is the incorporation of polycrystal plasticity simulations to model a large range of virtual microstructures that have not been experimentally realized (processed), which append the experimentally available microstructures. Simulations of cyclic responses with dwell periods for this range of virtual (and limited experimental) polycrystalline microstructures will be used to (i) provide additional data to optimize parameter fitting for a microstructure-insensitive macroscopic internal state variable (ISV) model with thermal recovery and rate dependence relevant to the temperatures of interest, and (ii) provide input to train an artificial neural network that will associate the macroscopic ISV model parameters with microstructure attributes for this material. Such microstructure sensitive macroscopic models can then be employed in component level finite element studies to model cyclic behavior with dwell times at smooth and cracked notched specimens.
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Brewster, G. J. J. "Solidification and heat-treatment related defects in single crystal nickel-base superalloys." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596900.
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This thesis examines the causes of surface scale, surface inter-dendritic phase formation and surface melting. These effects hinder component inspection and lead to extensive rework operations and component scrap. Surface scale is a region of colouration observed on the external surface of cast components. It has been shown to occur in the solid-state and to result from the differential thermal contraction between the mould and metal, driving separation during the casting process. The regions of the casting that separate from the mould are exposed to the casting atmosphere, resulting in the formation of a thin oxide interference film, or surface scale. The separation of the mould and metal in the solid state can cause the semi-solid ‘mush’ above to contract, resulting in segregated liquid flow towards the surface and a layer of inter-dendritic phases at the surface of the casting. Therefore a close relationship between surface inter-dendritic phase formation and the spatial occurrence of surface scale is observed. After heat-treatment a number of components exhibit ‘blisters’ of melted material at the surface, even in under-solutioned components. Surface melting frequently occurs within the scaled regions of turbine blade components, however the reasons for this were previously not understood. The increased risk of inducing melting of these lower melting point inter-dendritic phases on the surface associated with surface scale rationalizes this observation.
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Ge, Yindong. "HIGH CYCLE FATIGUE STUDIES OF CARBURIZED NICKEL-BASE SUPERALLOYS AND STAINLESS STEELS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1244230393.
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Knoche, Elisabeth Marie. "Influence of the precipitate size on the deformation mechanisms in two nickel-base superalloys." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/influence-of-the-precipitate-size-on-the-deformation-mechanisms-in-two-nickelbase-superalloys(8b80d24c-62de-4741-a827-4fb5a10c752b).html.
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The polycrystalline nickel-base superalloys RR1000 and Udimet 720Li (U720Li) were developed for turbine disc applications. These alloys contain a higher volume fraction of the ordered γ' phase (close to 50%) when compared to previous generation alloys (~ 25%) in order to ensure that they retain high strength at operating temperatures exceeding 700°C. The increased percentage of precipitates in the material leads to higher levels of constraint between matrix and the precipitates, and this will have consequences for the deformation mechanisms of the aggregate. It is therefore important to understand how the increased volume fraction of precipitates affects the deformation behaviour of the material. This is not only crucial for the design of the optimum microstructure, but also for lifing models, which predict the lifetime of a component. It is the aim of the present work to improve the understanding of the deformation behaviour of these alloys by focussing on the influence of the γ' precipitate size. These alloys usually comprise a complex trimodal γ' size distribution, which complicates studies on the dependence of the deformation behaviour on the precipitate size. Hence, simplified model microstructures were generated here with a unimodal γ' size distribution. The model microstructures were subjected to in-situ loading experiments with neutron diffraction at temperatures of 20°C, 500°C and 750°C. Neutron diffraction measurements during loading revealed the elastic lattice strain response of both the γ and the γ' phases, which can indicate changes in their respective deformation behaviour. These measurements showed a load transfer from γ to γ' for some test conditions, which indicated that γ was able to deform with noticeably less deformation in the γ' phase. With a larger γ' precipitate size and/or higher test temperature, the tendency for load transfer increased. A post-mortem analysis of the deformed microstructures using advanced electron microscopy techniques (EBSD, ECCI, TEM) showed that shearing of the γ' precipitates dominated the deformed microstructures at 20°C and 500°C and was also observed after deformation at 750°C. Deformation was less localised in the microstructures with large γ' precipitates, which might be correlated with the increased trend for load transfer. The onset of multiple slip or the activation of Orowan looping as an additional deformation mechanism are suggested as possible explanations for these observations.
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Chen, J. H. "Oxidation of nickel-base superalloys for turbine disc and advanced turbine blade applications." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597544.
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Isothermal and cyclic oxidation tests were carried on three "chromia" forming superalloys, Astroloy, Udimet 720 and Waspaloy used as turbine disc materials, and two advanced single crystal superalloys, CMSX4 and RR3000, developed as turbine blade materials, with and without Pt-aluminide coatings. For the turbine disc materials, external chromia scales were formed to protect the alloy substrate and also some internal oxidation developed. The oxidation behaviour was mainly related to the contents of aluminium, chromium and titanium and also the microstructure. For "alumina" forming superalloys without coatings, both CMSX4 and RR3000 formed a continuous alumina subscale after a period of transition oxidation at temperatures above 1000oC in isothermal tests. However the two alloys cannot form an alumina scale at 900oC and thus the growth rate of scale at 900oC was higher than at higher temperatures. The reduction of sulphur content to less than 1 ppm in CMSX4 was shown to improve the scale adhesion in the cyclic tests. For the Pt-aluminide coated CMSX4 and RR3000 excellent oxidation resistance was revealed in both isothermal and cyclic tests at 1100oC due to the formation of adherent alumina scale on the surface. As a result, the oxidation behaviour was very similar between the isothermal and cyclic tests. A deleterious effect was found in the interdiffusion zone of the Pt-aluminide coated alloys due to void and microcrack formation. This was attributed to the inward diffusion of platinum which caused the formation of needle-like TCP phases due to the high contents of rhenium in the two alloys.
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Kirka, Michael. "Thermomechanical behavior of a directionally solidified nickel-base superalloys in the aged state." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53458.
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Understanding the effects of aged microstructures on the thermomechanical fatigue (TMF) properties of nickel-base (Ni-base) superalloys remains unclear. Few experimental results are currently available in this area, and of the limited results available, some promote aged microstructures as beneficial, while others as detri- mental. The importance of these aged structures arises from the fact that when components used in the hot sections of gas turbine engines remain in service for ex- tended periods of time, the local temperature and stress provides the catalyst for the evolution of the microstructure.
An experimental assessment of a negative misfit directionally solidified (DS) Ni- base superalloy was undertaken to characterize the aging kinetics and understand the influence of the TMF cycle temperature extremum, temperature-load phasing, mean strain, creep-fatigue, orientation effects, and microstructure on TMF fatigue crack initiation. To determine the effects of aging on the TMF response, the as-heat- treated alloy was artificially aged to three unique microstructures identified in the aging kinetics study. The experiments revealed that not all aged microstructures are detrimental to the fatigue life behavior. Specifically, when the γ′ precipitates age in a manner to align themselves parallel to the axis of the applied stress, an increase in the fatigue life over that of the as-heat-treated microstructure is observed for out-of-phase TMF with dwells.
To extend the experimental understanding of the aged microstructures into ser- vice component design and life analysis, a temperature-dependent crystal viscoplas- ticity (CVP) constitutive model is developed to capture the sensitivity of the aged microstructure through embedding additional variables associated with the current state of the γ′ particles. As a result of the adaptations, the CVP model has the ability to describe the long-term aging effects of directional coarsening relevant to the analysis industrial gas turbine hot section components.
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Meher, Subhashish. "Comparative Coarsening Kinetics of Gamma Prime Precipitates in Nickel and Cobalt Base Superalloys." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc699871/.
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The increasing technological need to push service conditions of structural materials to higher temperatures has motivated the development of several alloy systems. Among them, superalloys are an excellent candidate for high temperature applications because of their ability to form coherent ordered precipitates, which enable the retention of high strength close to their melting temperature. The accelerated kinetics of solute diffusion, with or without an added component of mechanical stress, leads to coarsening of the precipitates, and results in microstructural degradation, limiting the durability of the materials. Hence, the coarsening of precipitates has been a classical research problem for these alloys in service. The prolonged hunt for an alternative of nickel base superalloys with superior traits has gained hope after the recent discovery of Co-Al-W based alloys, which readily form high temperature g precipitates, similar to Ni base superalloys. In the present study, coarsening behavior of g precipitates in Co-10Al-10W (at. %) has been carried out at 800°C and 900°C. This study has, for the first time, obtained critical coarsening parameters in cobalt-base alloys. Apart from this, it has incorporated atomic scale compositional information across the g/g interfaces into classical Cahn-Hilliard model for a better model of coarsening kinetics. The coarsening study of g precipitates in Ni-14Al-7 Cr (at. %) has shown the importance of temporal evolution of the compositional width of the g/g interfaces to the coarsening kinetics of g precipitates. This study has introduced a novel, reproducible characterization method of crystallographic study of ordered phase by coupling of orientation microscopy with atom probe tomography (APT). Along with the detailed analysis of field evaporation behaviors of Ni and Co superalloys in APT, the present study determines the site occupancy of various solutes within ordered g precipitates in both Ni and Co superalloys. This study has explained the role of structural and compositional gradients across the precipitates (g)/matrix (g) interfaces on the coarsening behavior of coherent precipitates in both Ni and Co-base superalloys. The observation of two interfacial widths, one corresponding to a structural order-disorder transition, and the other to the compositional transition across the interface, raises fundamental questions regarding the definition of the interfacial width in such systems. The comparative interface analysis in Co and Ni superalloy shows significant differences, which gives insights to the coarsening behaviors of g precipitates in these alloys. Hence, the principal goal of this work is to compare and contrast the Co and Ni superalloys and also, to accommodate atomic scale information related to transitions across interfaces to coarsening models for a better practical applicability of coarsening laws to various alloys.
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Palmert, Frans. "Crack growth in single crystal nickel base superalloys under isothermal and thermomechanical fatigue." Licentiate thesis, Linköpings universitet, Konstruktionsmaterial, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-153619.
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This work concerns the fatigue crack growth behaviour of nickel base single crystal superalloys. The main industrial application of this class of materials is in gas turbine blades, where the ability to withstand severe mechanical loading in combination with high temperatures is required. In order to ensure the structural integrity of gas turbine blades, knowledge of the fatigue crack growth behaviour under service-like conditions is of utmost importance. The aim of the present work is both to improve the understanding of the crack growth behaviour of single crystal superalloys and also to improve the testing and evaluation methodology for crack propagation under thermomechanical fatigue loading conditions. Single crystal superalloys have anisotropic mechanical properties and are prone to localization of inelastic deformation along the close-packed planes of the crystal lattice. Under some conditions, crystallographic crack growth occurs along these planes and this is a complicating factor throughout the whole chain of crack propagation life simulation; from material data generation to component calculation. Fatigue crack growth testing has been performed, both using conventional isothermal testing methods and also using thermomechanical fatigue crack growth testing. Experimental observations regarding crystallographic crack growth have been made and its dependence on crystal orientation and testing temperature has been investigated. Quantitative crack growth data are however only presented for the case of Mode I crack growth under isothermal as well as thermomechanical fatigue conditions. Microstructural investigations have been undertaken to investigate the deformation mechanisms governing the crack growth behaviour. A compliance based method for the evaluation of crack opening force under thermomechanical fatigue conditions was developed, in order to enable a detailed analysis of the test data. The crack opening force evaluation proved to be of key importance in the understanding of the crack driving force under different testing conditions.In the printed version of the thesis the series name Linköping Studies in Science and Technology Licentiate of engineering thesis is incorrect. The correct series name is Linköping Studies in Science and Technology Licentiate thesis.
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YU, FENG. "NONDESTRUCTIVE EVALUATION OF NEAR-SURFACE RESIDUAL STRESS IN SHOT-PEENED NICKEL-BASE SUPERALLOYS." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1130282650.
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Westbrooke, Eboni F. "Effect of crystallographic orientation on plastic deformation of single crystal nickel-base superalloys." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011466.
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Orozco-Smith, Evelyn M. "Analysis of low cycle fatigue properties of single crystal nickel-base turbine blade superalloys." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0014339.
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Stekovic, Svjetlana. "Low Cycle Fatigue and Thermo-Mechanical Fatigue of Uncoated and Coated Nickel-Base Superalloys." Doctoral thesis, Linköpings universitet, Konstruktionsmaterial, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-9820.
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High strength nickel-base superalloys have been used in turbine blades for many years because of their superior performance at high temperatures. In such environments superalloys have limited oxidation and corrosion resistance and to solve this problem, protective coatings are deposited on the surface. The positive effect of coatings is based on protecting the surface zone in contact with hot gas atmosphere with a thermodynamically stable oxide layer that acts as a diffusion barrier. During service life, mechanical properties of metallic coatings can be changed due to the significant interdiffusion between substrate and coating. There are also other degradation mechanisms that affect nickel-base superalloys such as low cycle fatigue, thermo-mechanical fatigue and creep. The focus of this work is on a study of low cycle fatigue and out-of-phase thermo-mechanical fatigue behaviour of three uncoated and coated nickel-base superalloys. Polycrystalline IN792 and two single crystals CMSX-4 and SCB were coated with four different coatings; an overlay coating AMDRY997 (NiCoCrAlYTa), a platinum aluminide modified diffusion coating RT22 and two innovative coatings with a NiW interdiffusion barrier in the interface called IC1 and IC3. A low cycle fatigue and thermo-mechanical fatigue device was designed and set-up to simulate service loading of turbine blades and vanes. The low cycle fatigue tests were run at 500oC and 900oC while the thermo-mechanical fatigue tests were run between 250oC and 900oC.To simulate long service life, some coated specimens were exposed at 1050oC for 2000 h before the tests. The main conclusions are that the presence of the coatings is, in most cases, detrimental to LCF lives of the superalloys at 500oC while the coatings do improve the LCF lives of the superalloys at 900oC. Under TMF loading conditions, the coatings have negative effect on the lifetime of IN792. On single crystals, they are found to improve TMF life of the superalloys, especially at lower strains. The tests also indicate that long-term aging influences the fatigue and fracture behaviour of coated superalloys by oxidation and diffusion mechanisms when compared to non-aged specimens. The aged specimens exhibit longer life in some cases and shorter life during other test conditions. Fatigue cracks were in most cases initiated at the surface of the coatings, growing transgranularly perpendicular to the load axis.
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Šteković, Svjetlana. "Low cycle fatigue and thermo-mechanical fatigue of uncoated and coated nickel-base superalloys /." Linköping : Department of Managenet and Engineering, Linköping University, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-9820.
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West, Scott Lewis. "A study of weld heat-affected zone liquation cracking in cast nickel-base superalloys." Connect to resource, 1991. http://rave.ohiolink.edu/etdc/view.cgi?acc%5Fnum=osu1248456984.
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Mai, Ronny. "Thermo-mechanical fatigue investigations on Nickel base superalloys and creep of NiAl thin films." Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2492.
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In service, many components and structures of aero jet engines, are exposed to a complex superposition of varying mechanically and thermally induced forces. This cyclic loading is most pronounced during the start-up and the shut-down sequence of the engine, usually combined with high temperature transients, and is responsible for a serious reduction in lifetime, compared to isothermal operating conditions. A detailed knowledge of this interaction between varying temperatures and loads is of considerable importance for precise lifetime calculations. In order to characterise and scientifically describe the material behaviour under thermo-mechanical fatigue (TMF) exposure, laboratory experiments are performed under strictly defined conditions. The main challenge for experimental investigations is the precise temperature control required to simulate the fast thermal transients under operating conditions. In any component, the lifetime behaviour is dominated by three different damage mechanisms: fatigue, oxidation and creep. In order to protect the component surface against oxidising atmosphere in gas turbines the substrate material is coated with different protective coating systems. This work compares the thermal mechanical fatigue behaviour of two different substrate materials, Nimonic 90 as the “classic” matrix and PM1000, an oxide dispersoide strengthened powder metallurgical superalloy under TMF loadings. Additionally, the creep behaviour and the lifetime analysis of a b−nickel aluminide diffusion coating system is described.
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Bowman, R. R. (Randy R. ). "Effect of melt spinning on the microstructure and mechanical properties of three nickel base superalloys." Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/11301.
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Bansal, Rohan. "Analysis and feedback control of the scanning laser epitaxy process applied to nickel-base superalloys." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51714.
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Scanning Laser Epitaxy (SLE) is a new layer-by-layer additive manufacturing process being developed in the Direct Digital Manufacturing Laboratory at Georgia Tech. SLE allows for the fabrication of three-dimensional objects with specified microstructure through the controlled melting and re-solidification of a metal powder placed atop a base substrate. This dissertation discusses the work done to date on assessing the feasibility of using SLE to both repair single crystal (SX) turbine airfoils and manufacture functionally graded turbine components. Current processes such as selective laser melting (SLM) are not able to create structures with defined microstructure and often have issues with warping of underlying layers due to the high temperature gradients present when scanning a high power laser beam. Additionally, other methods of repair and buildup have typically been plagued by crack formation, equiaxed grains, stray grains, and grain multiplication that can occur when dendrite arms are separated from their main dendrites due to remelting. In this work, it is shown that the SLE process is capable of creating fully dense, crack-free equiaxed, directionally-solidified, and SX structures. The SLE process, though, is found to be currently constrained by the cumbersome method of choosing proper parameters and a relative lack of repeatability. Therefore, it is hypothesized that a real-time feedback control scheme based upon a robust offline model will be necessary both to create specified defect-free microstructures and to improve the repeatability of the process enough to allow for multi-layer growth. The proposed control schemes are based upon temperature data feedback provided at high frame rate by a thermal imaging camera. This data is used in both PID and model reference adaptive control (MRAC) schemes and drives the melt pool temperature during processing towards a reference melt pool temperature that has been found to give a desired microstructure in the robust offline model of the process. The real-time control schemes will enable the ground breaking capabilities of the SLE process to create engine-ready net shape turbine components from raw powder material.
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Oncina, Carlos Andrés. "Pre-diffusion to improve the thermal fatigue strength of overlay coatings on nickel-base superalloys." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14429.
Full textAbstract:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1989.Includes bibliographical references.
Partial financial support provided through the National Science Foundation. DMR-10217
by Carlos Andrés Oncina.
M.S.
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Burba, Micheal Eric. "Microstructure-Sensitive Models for Predicting Surface Residual Stress Redistribution in P/M Nickel-Base Superalloys." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1492532628147262.
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