Dissertations / Theses on the topic 'Cobalt base superalloys'
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1
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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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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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
4
Wertz, Katelun N. "Exploration of Phase Stability and Hot Workability of Polycrystalline Co-Al-W-Base Superalloys." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555455335988532.
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Salgado, Marcus Vinicius da Silva. "Processamento e caracterização de ligas do sistema Co-Ni-Al-W-Cr-(Nb,Ta)-C-B visando aplicação como material de ferramenta para soldagem por atrito." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-03122015-155841/.
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Os objetivos deste trabalho foram processar e caracterizar microestrutural e mecanicamente superligas à base de cobalto do sistema Co-Al-W-Ni-Cr-(Nb,Ta)- C-B com microestrutura ?/?\'. Visando possível aplicação em ferramenta para Soldagem por Atrito com Pino Não Consumível (SAPNC), em inglês Friction Stir Welding (FSW) nas composições: (Co-10Al-7,5W-30Ni-10Cr-3,0Nb-0,6C-0,06B %at. ) - 30Ni-3Nb, (Co-10Al-7,5W-40Ni-10Cr-3,0Nb-0,6C-0,06B %at.) - 40Ni-3Nb, (Co-10Al-7,5W-50Ni-10Cr-3,0Nb-0,6C-0,06B %at.) - 50Ni-3Nb além da liga patenteada (Co-10Al-7,5W-40Ni-10Cr-3,0Ta-0,6C-0,06B %at.) - 40Ni-3Ta considerada padrão para este projeto. A caraterização microestrutural foi feita por microscopia eletrônica de varredura (MEV), microscopia eletrônica de varredura por emissão de campo (MEV-FEG), medidas de microanálise semi-quantitativa e mapeamento químico por EDS, caracterização por difração de raios X, além do ensaio mecânico de dureza Vickers em todas as amostras. Os resultados da caracterização microestrutural e mecânica para a liga 40Ni-3Ta mostraram-se semelhantes aos encontrados na literatura enquanto que a composição 40Ni-3Nb foi a que apresentou resultados mais próximos em relação à liga padrão.The objectives of this study were to process and characterize microstructural and mechanical cobalt-based superalloys from Co-Al-W-Ni-Cr-(Nb,Ta)-C-B system with ?/? \' microstructure. Aiming possible application for Friction Stir Welding (FSW) tool in the compositions: (Co-10Al-7.5W-30Ni-10Cr-3.0Nb-0.6C-0.06B %at.) - 30Ni-3Nb, (Co-10Al-7.5W-40Ni-10Cr-3.0Nb-0.6C-0.06B %at. ) - 40Ni-3Nb, (Co-10Al-7.5W-50Ni-10Cr-3.0Nb-0.6C-0.06B %at.) - 50Ni-3Nb, including the patented alloy (Co-10Al-7.5W -40Ni-10Cr-3.0Ta-0.6C-0.06B %at.) - 40Ni-3Ta considered the standard alloy for this project. The microstructural characterization was made by Scanning Electron Microscopy (SEM), Scanning Electron Microscopy with Field Emission Gun (SEM-FEG), semi-quantitative microanalysis measures and chemical mapping by EDS, characterization by X - ray diffraction and mechanical test of hardness Vickers in all the samples. The results of the microstructural and mechanical characterization for 40Ni-3Ta alloy were similar to those found in the literature. The 40Ni-3Nb alloy showed the closest results, among the other alloys studied in comparison with the standard alloy.
6
Weaver, Donald S. "Thermomechanical Processing of a Gamma-Prime Strengthened Cobalt-Base Superalloy." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1543508199900005.
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Huron, Eric S. "High temperature monotonic and cyclic deformation in a directionally solidified nickel-base superalloy." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/16093.
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Dupin, Nathalie. "Contribution à l’évaluation thermodynamique des alliages polyconstitués à base de nickel." Grenoble INPG, 1995. http://www.theses.fr/1995INPG0040.
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La coexistence des phases gamma de structure cubique a faces centrees a1 et gamma' de structure cubique a faces centrees l1#2 confere aux superalliages base nickel leurs exceptionnelles proprietes mecaniques a hautes temperatures. Des calculs thermodynamiques bases sur l'evaluation des systemes simples constitutifs de ces alliages complexes, contenant au moins huit elements, peuvent permettre de reduire le nombre d'experimentations a entreprendre pour optimiser leur compositions et les traitements thermiques associes. Dans ce but, ce travail presente l'etude thermodynamique des phases constituant les systemes quaternaires al-cr-ni-ta et al-cr-ni-ti. La premiere partie presente les modeles adaptes a la description du comportement thermodynamique des phases intermetalliques etudiees. La presentation du modele en sous-reseaux est particulierement detaillee. Les contraintes necessaires a la description des phases a1 et l1#2 par une meme expression mathematique sont derivees a partir de l'identification des modeles a deux et quatre sous-reseaux de la phase l1#2. Les chapitres suivants analysent les systemes binaires al-co, al-ni, cr-ta et ternaires al-co-ni, al-cr-ni, al-ni-ti, al-ni-ta, cr-ni-ta et cr-ni-ti. Les parametres thermodynamiques decrivant les phases constituant ces systemes sont obtenus dans un processus d'optimisation prenant en compte l'ensemble des donnees experimentales, souvent rares, publiees sur ces systemes. L'extension des parametres thermodynamiques ainsi determines aux systemes quaternaires al-cr-ni-ta et al-cr-ni-ti sans optimisation supplementaire justifie la demarche entreprise. Une base thermodynamique permettant le calcul des equilibres de phases dans les superalliages base nickel a donc ainsi ete constituee
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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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Bouzaher, Abdallah. "Réseau bipériodique de dislocations d'hétéro-interface en élasticité anisotrope." Grenoble INPG, 1993. http://www.theses.fr/1993INPG0089.
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Dans ce travail un modele original de calcul des champs elastiques des reseaux hexagonaux de dislocations d'hetero-interfaces est propose en elasticite anisotrope. Les conditions aux limites sont les suivantes: a) les dislocations sont intrinseques et n'engendrent pas de contraintes a longue distance. B) la condition de raccordement des deux milieux a l'interface est representee par un deplacement relatif lineaire a l'interieur d'un hexagone, et discontinue le long de ses cotes. Les champs des deplacements et des contraintes sont etablis et calcules numeriquement par des programmes fortran. Une formule analytique, obtenue par integration, est etablie pour determiner l'energie elastique stockee par unite de surface du joint. Elle est appliquee dans les cas suivants: a) hetero-interface cu/fe, b) hetero-interface cosi#2/si, c) hetero-interface gamma/gamma dans les superalliages, d) joints de torsion dans les metaux cfc
12
Yasin, Muhammad. "Hot corrosion behavior of modified aluminide coatings on cobalt-base superalloys." Thesis, 1986. http://hdl.handle.net/10945/21894.
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Singh, Mahander Pratap. "On understanding the role of V addition in design and development of high specific strength γ'(L12)-strengthened Co-base superalloys." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4928.
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Ni-based superalloys with excellent mechanical, thermal and oxidation resistance properties have great demand in energy applications. Over the time, varied compositions of Ni-based superalloys have been utilized for the fabrication of aero-based and land-based turbines. Recently, these are also proposed as key alloys for construction of Advanced Ultra-supercritical (AUSC) plants.
Co has 40 ºC higher melting temperature than Ni, and offers superior sulfidation, hot corrosion and thermal fatigue resistance at elevated temperatures. Recent discoveries suggest that Co-based superalloys having similar microstructure to Ni-based superalloys can be synthesized with base compositions of Co-Al-W or Co-Al-Mo-Nb/Ta. Further developments of these demonstrated that Co-base superalloys can be a promising alternative to Ni-based superalloys. The major challenges with the Co-based superalloys development is to (a) obtain a high γʹ(L12)-solvus temperature, (b) low mass density, (c) high specific strength at elevated temperatures, (d) long-term microstructural stability (e) better creep properties and (f) optimum oxidation resistance.
In the current work, V is investigated as a potential additive in Co-Al based system to produce γʹ(L12)-strengthened Co-base superalloys. V having complete solid solubility with Mo was systematically replaced in base composition of Co-10Al-5Mo-2Nb alloy, earning benefits in γʹ-solvus temperature and mass density. A detailed microscopic characterization and microanalysis studies on the developed Co-10Al-5V-2Nb alloy demonstrated the role of V and its interaction with other participating elements in γ- and γʹ- phases. This further guided development of a novel γʹ-strengthened Co-Al-V ternary system. In a further endeavour, Ni and Ti was added, which led to design a new class of low-density Co-based super alloys. In a parallel effort, oxidation behaviour of the developed Co-Ni-Al-Ti-Nb-V alloy was studied at 800 ºC and 900 ºC. Addition of Cr significantly inhibits the accelerated corrosion of the V containing alloys. These results can provide beneficial inputs for the development of new class of γʹ(L12)-strengthened Co-based superalloys.
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Tsang, Chang An, and 臧建安. "Solidification Structure and Aging Behavior of Cobalt-base Superalloy Welds." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/55390005163911142722.
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Lin, Hung-Mao, and 林宏茂. "Wear Characteristics of Cobalt-Base Superalloy Melted by Plasma Transferred Arc." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/58682864186818194987.
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碩士國立成功大學
材料科學(工程)學系
86
The surface overlaying treatment is aimed to give different special properties to surfaces and substrates of materials. Microhardness, wear-resistance, corrosion-resistance etc. can be enhanced after treatment. Due to superior mechanical properties, spheroidal graphite (SG) cast irons are widely used in industries such as machine production, automobile components etc. These components generally need to have surfaces with higher microhardness to increase wear-resistance while their cores need to main The results reveal that the overlayer specimen after overlaid can be divided into overlayer, interface region and substrate. The interface region includes interfacial layer and partially melted region which is mainly composed of fine pearlite and ledeburite. The substrate includes heat effect region. The Stellite 6 overlayer melted on SG iron cast with 3.5wt% carbon under low overlaying current (I=140A) is a dentritic structure with M7C3 and M23C6 carbides. On the other hand, the Stellite 1 overlaye The microhardness of Stellite alloy overlayers increases with overlaying currents and so does the amount of carbides. The main reason is that the overlayers are diluted by substrates. Hence, it shows that the microhardness of overlayers is related to overlaying current and the amount of carbides. The results of cutting wear test reaveal that the flank wear width of Stellite alloy overlayers tend to increase as the sliding distance and cutting speed . The flank wear width of Stellite 6 overlayer redu In the cutting wear test, the wear mechanisms of overlayers are mainly plastic groove, surface polish and adhesive wear as adhered to overlayers. Others minor mechanisms include brittle crack and fracture. Among these, the case to plastic groove include microcutting and plough.
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Hou-YuCiou and 邱厚諭. "Formability Analysis of HA-188 Cobalt-base Superalloy in Tube Hydroforming." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/19914184737800093915.
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Tsai, Dir-Don, and 蔡德東. "research of surface integrity of an EDMed cobalt-base superalloy(Elgiloy)." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/02775698302213862024.
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碩士國立中央大學
機械工程學系
85
ABSTRACTan advanced adaptive control cnc edmmachine is adopted in this research,and keroseneis used as a primary working fluid( dielectric). a minute energy edm machining is operatedin this experiment through various settings ofworking conditions(such as change of electrodepalarity,electrode material,discharge duration,discharge current,planetary motion of electrode, aluminum powderaddition in dielectric and Elgiloy workpiece material status etc)and an optimal edm working condition is obtainedthrough analyzing the results of working efficiency(such as material removal rate and relativeelectrode wear ratio)and surface integrity(such as surface roughness,microcrack,EDAX,EPMA and sectionalmicrohardness etc)
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Li, Han-yun, and 黎瀚揚. "Corrosion Behavior and Electrochemical Properties of Commercial Cobalt-based Superalloy." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/23354580752903028757.
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碩士中國文化大學
材料科學與奈米科技研究所
99
This research made use of different chlorine concentrations and temperatures to explain the commercial cobalt-based super-alloys electrochemical properties and corrosion behavior of the commercial cobalt-based super-alloys in terms of the electrochemical polarization curves. Both SEM and the immersion experiments were used to explain the micro-structure and to understand the effect of temperature and concentration on the pit size. Several different solutions and concentrations were also applied to confer the critical pitting temperature (CPT) of the cobalt-based super-alloys. In three different chloride salts, the corrosion potential (Ecorr) are of little change of temperature and concentration, and the pitting potential (Eb) gradually decreased as temperature increases. Among them, Fecl3 is a rather special case in which the difference between Ecorr and Eb in potential are relatively small which implies the alloy immediately pitted right after the specimen being scanned beyond the Ecorr. The corrosion morphology of the alloy tested in three kinds of chloride solutions at 80oC observed by SEM shows that the corrosion all initiated preferentially at the interdendritic regions which were eventually merged into larger area as time goes on; the damage were particularly pronounced for Fecl3 than the other two.
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Sharma, Abhishek. "An Evaluation of the Mechanical Behavior of some new High Temperature Materials." Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5254.
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Two new high-temperature alloy systems have been discovered recently at the Indian
Institute of Science, which form the basis of this thesis. The first alloy system is an
Intermetallic-Intermetallic eutectic composite alloy in the nickel-rich end of the Ni-Al-
Zr ternary system, first reported by Tiwary et al. These eutectic composites have very
impressive room temperature yield strengths of about 2 GPa which are retained till
about 700 . Coupled with 2 to 5% tensile plasticity at room temperature, excellent
high-temperature oxidation resistance, good long-term microstructural stability and very
low densities of about 7.35–7.95 gm/cm3, these materials are exciting candidates for
high-temperature applications.
The second alloy system comprises of Tungsten free Cobalt based superalloys having
the classical
−
0 microstructure similar to that of nickel-based superalloys as described
by Makineni et al. The presence of the L12 phase in cobalt-based systems was reported
by Lee et al. and Sato et al. where the addition of 25 wt.% tungsten seemed to stabilize
the metastable Co3Al. This however pushed the density of the alloy to about 9–10
gm/cm3, making it too heavy for most high-temperature applications. A large body of
work followed trying to reduce or eliminate the presence of tungsten in these alloys. The
new alloys by Makineni et al. do not contain tungsten which reduces the density to about
8.0–8.4 gm/cm3.
The high-temperature mechanical behavior of some of the alloys from these two sysi
tems has been evaluated in the current thesis. This thesis is divided into six chapters.
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Benson, Michael Lee. "Strain-Induced Phase Transformation and Anisotropic Lattice-Strain Development in a Cobalt-Based Superalloy." 2008. http://trace.tennessee.edu/utk_graddiss/327.
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This dissertation addresses two issues concerning the deformation behavior of a cobalt-based superalloy: 1) the strain-induced face-centered-cubic to hexagonal-closepacked phase transformation and 2) the anisotropic lattice-strain development. Cobaltbased alloys are known to exhibit a metastable face-centered-cubic crystal structure at room temperature. This structure can transform to the thermodynamically-stable hexagonal-close-packed phase upon application of a load. While this phenomenon has been studied and documented before, this work offers a more in-depth study on this issue, as it addresses the phase transformation under several loading modes: monotonic tension, monotonic compression, stress-controlled high-cycle fatigue, and strain-controlled lowcycle fatigue. The experimental technique utilized in this research is neutron diffraction. This nondestructive method is particularly well suited to the problem because it can be used to study the transformation with the mechanical load applied in-situ.
Anisotropic lattice strain development is a natural problem to study, as neutron diffraction is also well suited for this measurement. Individual crystallites in a polycrystalline matrix by nature have directionally-dependent responses to the applied stress. When neighboring anisotropic grains interact, inhomogeneities known as intergranular strains develop. This dissertation assumes that the total lattice strain is the sum of two contributions: the linear-elastic contribution and the plasticity-induced intergranular contribution. Within the context of this analysis, the effect of the phase transformation on the deformation behavior is also inferred.
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Chan, Wai-Sing, and 陳偉聲. "Overlaying Characteristics of Cobalt-Base Superalloy Formed on Spheroidal Graphite Cast Iron by Plasma Transferred Arc Melting Process." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/97299387388451847426.
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博士國立成功大學
材料科學(工程)研究所
84
The purpose of this study is to overlay an alloy with high wear and corrosion resistant on SG cast irons in order to widen its application. Stellite 1,6 and 21 alloys were overlaid on SG cast irons with various carbon and silicon contents by plasma trans- ferred arc process. Furthermore, tearing property of the speci- mens after overlaying were also invertigated. Results revealed that the variation of the carbon and silicon contents has no effect on the solidification structure of the overlayers with low overlaying current. The solidification structure of the Stellite 1 overlayer is hypereutectic while the Stellite 6and 21 are den- dritic. An interfacial layer which contain large amount of car- bides formed at the interface region between three overlayers and high carbon content substrate. The occurrence of interfacial layer is detrimental to the bonding strength of overlaid speci- mens. The formation of interfacial layer cannot be inhibited by increasing silicon content of substrate. On the other hand, the amount of interfacial layer decreases with decreasing carbon con- tent of the substrate. Tearing strength increased as the amount of the interfacial layer decreased. The overlayers of the high overlaying current specimens are iron rich, this indicated that the overlayers were highly diluted by the substrate, and the tearing strength of these specimens is low. Tearing strength in- creased when the carbon content of substrate decreased.
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Jheng, Ming-Hong, and 鄭名翃. "Effect of Hot Isostatic Pressure and Addition of Cobalt Element on High-Temperature Creep of CM-681LC Ni-Base Superalloy." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/arxv7f.
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碩士義守大學
材料科學與工程學系
106
In this study, CM-681LC nickel-base superalloy was used as the base material to investigate the difference of microstructure and the influence of high temperature creep behavior by Cobalt element addition (+3%) and hot isostatic pressure process. Experimental procedure firstly uses the vacuum induction melting furnace to make the directionally solidified specimens, three-stage heat treatments (solution treatment at 1270°C/4hr/ArC, primary aging at 1038°C/2hr/ArC and secondary aging at 870°C/20hr/ArC), and then ultra-high temperature creep (1050°C/200MPa) experiment. In addition, by increasing the cobalt content and/or performing the hot isostatic pressure process to improve the ultra-high temperature creep life were investigated, and the differences of microstructure were discussed. Analytical experiments employ X-ray diffraction analyzer to identify phases, scanning electron microscope and transmission electron microscope to observe the microstructures. Results show that the hot isostatic pressure process and/or the addition of cobalt element do not improve the ultra-high temperature creep life of directionally solidified CM-681LC nickel-based superalloy; however, the hot isostatic pressure process can enhance the ultra-high temperature creep life of directionally solidified CM-681LC nickel base superalloy with cobalt addition.
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Makineni, Surendra Kumar. "Improvement of High Temperature Strength of Al and Co Alloy by L12 Type Coherent Precipitates." Thesis, 2015. https://etd.iisc.ac.in/handle/2005/4348.
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The present work aims at developing a new class of high temperature alloys based on ordered
intermetallic compound that forms coherently with the matrix during solid state transformation.
The chosen intermetallics have L12 ordered structure, which is a derivative of fcc unit cell.
Most popular example of this fcc derivative is Ni3Al that is critical in developing high strength
at high temperatures (~900°C) in commercially successful Ni based superalloys. Similar
ordered structures form either in stable or metastable form can act as a main strengthening
constituent in Al and Co matrices.
For example Al3Sc, Al3Zr, Al3Hf can be dispersed in fcc Al matrix that are stable at
temperatures ~ 400°C due to very low diffusivity of transition metals (Sc, Zr, Hf etc.) in the
matrix. However, due to low solid solubility of these transition metals, the obtained volume
fraction of these precipitates in the matrix is not sufficient to provide adequate room
temperature strength.
In fcc Co matrix, stable Co3Ti phase with L12 ordered structure forms with cuboidal
morphology. However, besides having lower melting point, the precipitates have large misfit
that lowers thermal stability at high temperatures. Recently, addition of Al and W with a proper
ratio in Co is reported to lead the formation of metastable Co3(Al,W) L12 ordered phase in fcc
α-Co matrix. This provides significant strength at high temperatures (~ 900°C). The main
drawback for these alloys is their high densities (9.6 to 10.5 gm.cm-3) due to the requirement of
compulsory addition of W (~ 15 to 25 wt%) for stabilising the ordered phase.
In the present work, these problems are overcome leading to the development of new class of
Al and Co alloys. The thesis is organized in three parts. In the first part, the principles of
strengthening that can be optimized to develop newer high temperature high strength alloys are
reviewed. The ordered L12 structure, which is the mainstay of the current effort of new alloy
development, is elaborated. In the second part we present the results of our effort to the
development a new class of high strength high temperature Al alloys. A new approach has been
adopted to get a microstructure that contains both high temperature stable and room
temperature strengthening precipitates. This has been illustrated by two Al rich compositions,
Al-2Cu-0.1Nb-0.15Zr and Al-2Cu-0.1Hf-0.15Zr (at% unless stated otherwise). Addition of
Nb/Zr or Hf/Zr in Al alloys leads to the formation of high temperature stable L12 ordered
spherical coherent precipitates in the fcc Al matrix. Cu addition gives room temperature
strengthening θ’ and θ” precipitates. The arc melted alloys were chill cast (suction cast) in the
form of 3 mm rods followed by a novel three stage heat treatment process, as shown below.
In the case of Al-2Cu-0.1Nb-0.15Zr alloy, the chill cast structure consists of Cu rich phase at
the boundaries along the α-Al dendrites while Zr and Nb partition inside the α-Al dendrites.
Aging at 400°C leads to an increase in the hardness of the cast alloy due to the precipitation of
coherent L12 ordered Al3(Zr,Nb) spherical precipitates (~5nm) in the α-Al dendrites. Zr
strongly partitions to the L12 ordered precipitate relative to the matrix. Nb exhibits weak
partitioning in the precipitate. Further solutionising was optimized at 535°C for 30 minutes
such that the segregation of Cu in the chill cast samples can be eliminated. The WDS mapping
shows that Cu dissolved uniformly in the α-matrix while the Zr/Nb enriched α-Al dendrites are
still present. The L12 ordered precipitates are mostly found in these Zr/Nb enriched dendrites
formed during solidification. The precipitates sizes are finer (~5 nm) in dendrites and larger in
the interdendritic region. The Nb partitioning increases in the ordered L12 precipitates relative
to the matrix after solutionising. On aging at 190°C, fine θ” precipitates nucleate on prior
Al3(Zr,Nb) precipitates present in α-Al dendrites while the interdendritic regions contain
coarser θ’ nucleated on larger size L12 precipitates. The θ”/θ’ are much finer and higher in
number density for the quaternary alloy compared to binary Al-2Cu alloy subjected to
conventional heat treatment. The quaternary alloy show higher peak hardness of 1500 ± 8 MPa
after 5 hours of aging at 190°C compared to binary Al-2Cu alloy with peak hardness of 1260 ±
11 MPa.
24
Ko, Chih-Chien, and 柯志建. "The Effects of Vacuum Sintering and Heat Treatments on the Microstructure and Mechanical Properties of Cobalt Based Superalloy after TiC Particles Dispersion Strengthening." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/65s9x7.
Full textAbstract:
碩士國立臺北科技大學
材料及資源工程系研究所
99
Cobalt-based superalloys are used extensively in applications requiring good wear resistance, corrosion resistance and heat resistance. Many of the properties of these alloys arise from the crystallographic nature of cobalt, the solid solution strengthening and carbide precipitation effects of chromium, tungsten and molybdenum. Metal matrix composites are known to exhibit exceptional wear resistance; therefore, several investigators have used titanium carbide (TiC) as a reinforcing medium in a ferrous metal matrix in order to enhance this property. TiC has proved its suitability in Fe or Fe-based alloys due its high hardness, low density and chemical stability with Fe-based alloys. In this study, we have mixed and added different amounts of TiC powders (10, 15 and 20 wt %) to the Cobalt-based superalloy powders. The mixing processed was finished by ball milling and granulation in a laboratory. In addition, the mixing powders (Cobalt-based superalloy and TiC) were sintered at 1260, 1270, 1280 and 1290°C, and then a series of HIP processes and heat treatments were performed. Meanwhile, the parameter of HIP treatment was 1250°C, 125 MPa and 100 min. The heat treatment processes were heating to 1100°C and maintaining for 40 min for quenching; aging at 760°C and soaking time was 6, 9, 12 h, respectively. Various materials characterization techniques were used to evaluate the materials’ properties and microstructures, including: apparent porosity, hardness test, transverse rupture strength (TRS) test, OM, and SEM microstructral examinations. The experimental results show that the highest TRS value of 1566.7 MPa was obtained by the 15 wt% TiC additive powder, which was sintered at 1280°C and then followed by HIP process and solid solution heat treatment. It also has been proved that the closed pores can be effectively eliminated (1.2% → 0.86%) by HIP treatment; in addition, the M6C carbides can produce more uniform precipitation on the grain-boundary and matrix after heat treatment. Furthermore, the highest hardness value of HRA 80.4 was obtained by the 20 wt% TiC additive powder, which was only sintered at 1290°C.