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Tesi sul tema "Heat resistant alloys"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 30 luglio 2024

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1

Al-Meshari, Abdulaziz I. "Metal dusting of heat-resistant alloys". Thesis, University of Cambridge, 2008. https://www.repository.cam.ac.uk/handle/1810/217872.

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Metal dusting leads to disintegration of such alloys as iron and nickel-based into a “dust” of particulate metal, metal carbide, carbon, and/or oxide. It occurs in strongly carburising environments at 400-900°C. Literature survey has shown that alloys behave differently in metal dusting conditions based on their composition and the environment. Metal dusting mechanisms for iron and nickel-based alloys have been proposed but, nevertheless, have not been agreed upon and numerous modifications to them have been suggested. Further adding to the complexity, the mechanisms were found to have differed due to operating condition alterations. In view of that, this research was carried out to gain a better understanding of metal dusting process(s) by evaluating the performance of heat-resistant alloys, namely KHR35C HiSi© (HP), KHR45A LC© (35Cr-45Ni), and UCX©, in metal dusting conditions. HP, which is an iron-based alloy, was modified by adding more silicon in order to improve its resistance through the development of SiO2 at the surface. The carbon content in the nickel-based alloy, 35Cr-45Ni, was lowered to delay the attack onset by accommodating more diffused carbon. UCX©, however, has the highest nickel and chromium levels. The alloys were exposed to a gas containing 80 vol% CO+20 vol% H2 at 650, 750, and 850ºC for 100, 500, and 1000h. Analyses including visual inspection, XRD, and SEM/EDX revealed that the alloys suffered localised attacks at the three temperatures but to varying degrees and in different shapes. In general, the attack initiated at the matrix rather than the primary carbides and also progressed through the matrix. Increasing the exposure temperature caused less carbon deposition and more oxides formation on the alloy surfaces leading to a reduction in the attack aggressiveness. UCX© exhibited the highest resistance to metal dusting whilst HP suffered the severest attack. The presence of high concentrations of chromium at the surface catalysed a quick formation of Cr2O3 scale that reduced the extent of metal dusting. Also, the increase in nickel content might have slowed down the carbon diffusion into the alloy. In addition, the presence of other oxide and carbide-forming elements such as silicon and tungsten might well have enhanced the alloy performance. Diffused carbon binds with free tungsten, niobium, and chromium to form carbides prolonging the incubation period prior to the attack initiation.

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2

From, Malin, Johanna Ejerhed, Artin Fattah, Markus Lindén e Alex Karlstens. "Heat Resistant Steel Alloys : Atlas Copco". Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-256662.

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Atlas Copco is interested in investigating the friction in the top-hammer drilling tool threads thatcauses the steel to heat up, leading to a phase transformation and a softer steel in the threads. Theaim of this project is to find a steel alloy or surface finishing that will retain its hardness atelevated temperatures better than the presently used threads material. The solution is intended tobe used as a replacement material for the threads. The potential material is meant to combat thepremature breakdowns of the threads and thus minimizing the economical losses. To achieve ourproject goal, literature studies and an experimental parts were employed.Hardening methods are discussed thoroughly in the thesis, such as carbides/nitrides,precipitation, solid solution, grain size, and martensitic transformation. Alloying elements andtheir effects on steels properties were also discussed. C, Cr, Co, Mn, Mo, Ni, W, and V werefound to increase the steel's hardness at elevated temperature, high temperature strength andabrasion wear resistance.Nitration can be applied to most of the steels that Atlas Copco uses today, and will give a harder,and more wear resistant surface at elevated temperatures. A problem with nitration is that thenitrided layer is generally thinner than the martensitic hardening used today.Three tool steels samples (ASP 2030, ASP 2053 and ASP 2060) were acquired from Erasteel.These were used in the experimental part and compared to reference steels that Atlas Copcocurrently are using (R1-R6). The experiments were conducted in 400 and 600°C and the sampleswere tempered for 1, 10 and 100 hours before the hardness were measured with a Vickershardness test. The conclusion from the experiments was that ASP 2060 and ASP 2053 fromErasteel are the steels that have a much higher hardness at elevated temperature than the othersteels tested in the experiment. The results indicate that the tool steels will probably notexperience the same premature breakdown as the threads used today. R1 and ASP 2053 have thegreatest heat resistance.The suggested tool steels are all quite expensive, and to minimize the material needed only thethreads and not the rod can be in the new alloy. Lowering the cost could also be achieved byhardfacing where a layer of the new expensive alloy is welded onto a cheaper steel.

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3

Nowak, Igor Mateusz. "Development of heat resistant alloys for optimal creep performance". Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5916/.

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Heat resisting centrifugally cast tubes of HP micro alloy (25/35 Cr/Ni, 0.4C), are extensively used in steam reforming, which is currently the dominate technology for hydrogen generation. High pressure of the reacting gases inside the tubes generates high hoop stress in the tube wall and together with the temperature exposure of 900-1050°C causes the tubes to creep along the circumferential direction. The alloy's ability to successfully withstand the severe operating condition is highly dependent on its high temperature creep-rupture behaviour. In recent years a number of manufactures have introduced higher creep-rupture strength versions of the heat resisting HP micro alloy. As a consequence they are able to offer the centrifugally cast tubes in thinner walls. Therefore, there is a need to enhance the creep-rupture strength of the alloy produced by Doncasters Paralloy. The immediate objective of this research project is to establish the mechanisms that govern the creep process in this alloy system. Once these mechanisms are better understood further alloy development within the present alloy composition can be achieved. The advanced stages of the project specifically involve studying the influence of microstructure in relation to creep resistance as a function of compositional modifications.

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4

Calmunger, Mattias. "On High-Temperature Behaviours of Heat Resistant Austenitic Alloys". Doctoral thesis, Linköpings universitet, Konstruktionsmaterial, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-122945.

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Advanced heat resistant materials are important to achieve the transition to long term sustainable power generation. The global increase in energy consumption and the global warming from greenhouse gas emissions create the need for more sustainable power generation processes. Biomass-fired power plants with higher efficiency could generate more power but also reduce the emission of greenhouse gases, e.g. CO2. Biomass offers no net contribution of CO2 to the atmosphere. To obtain greater efficiency of power plants, one option is to increase the temperature and the pressure in the boiler section of the power plant. This requires improved material properties, such as higher yield strength, creep strength and high-temperature corrosion resistance, as well as structural integrity and safety. Today, some austenitic stainless steels are design to withstand temperatures up to 650 °C in tough environments. Nickel-based alloys are designed to withstand even higher temperatures. Austenitic stainless steels are more cost effective than nickel-based alloys due to a lower amount of expensive alloying elements. However, the performance of austenitic stainless steels at the elevated temperatures of future operation conditions in biomass-red power plants is not yet fully understood. This thesis presents research on the influence of long term high-temperature ageing on mechanical properties, the influence of very slow deformation rates at high-temperature on deformation, damage and fracture, and the influence of high-temperature environment and cyclic operation conditions on the material behaviour. Mechanical and thermal testing have been performed followed by subsequent studies of the microstructure, using scanning electron microscopy, to investigate the material behaviours. Results shows that long term ageing at high temperatures leads to the precipitation of intermetallic phases. These intermetallic phases are brittle at room temperature and become detrimental for the impact toughness of some of the austenitic stainless steels. During slow strain rate tensile deformation at elevated temperature time dependent deformation and recovery mechanisms are pronounced. The creep-fatigue interaction behaviour of an austenitic stainless steel show that dwell time gives shorter life at a lower strain range, but has none or small effect on the life at a higher strain range. Finally, this research results in an increased knowledge of the structural, mechanical and chemical behaviour as well as a deeper understanding of the deformation, damage and fracture mechanisms that occur in heat resistant austenitic alloys at high-temperature environments. It is believed that in the long term, this can contribute to material development achieving the transition to more sustainable power generation in biomass-red power plants.

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5

Highsmith, Shelby. "Probabilistic fatigue crack life prediction in a directionally-solidified nickel superalloy". Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04082004-180222/unrestricted/highsmith%5Fshelby%5F200312%5Fms.pdf.

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6

Toh, Chin Hock Materials Science &amp Engineering Faculty of Science UNSW. "Metal dusting on heat-resistant alloys under thermal cyclic conditions". Awarded by:University of New South Wales. School of Materials Science and Engineering, 2002. http://handle.unsw.edu.au/1959.4/35011.

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Solid oxide fuel cells operate at elevated temperature, oxidising fuel gases to generate electricity. The fuel gas streams in the fuel cell systems are rich in carbon and have very low oxygen potential. Under these conditions, alloys can undergo metal dusting, which causes pitting or general thinning of the alloys. This process is not yet fully understood. It is, hence, not possible to accurately predict the susceptibility of a particular alloy in the atmospheres relevant to SOFC. Model Fe-Cr and Fe-Ni-Cr alloys were exposed to test the hypothesis that cementite formation and its decomposition is necessary for metal dusting to occur. A series of ferritic and austenitic engineering alloys were also exposed to compare their dusting rates. Two specimens of each alloy were studied, one was etched in a H3PO4-15%H2SO4-21%H2O solution and the other was ground to a 600-grit finish. The alloys were exposed to a CO-26%H2-6%H2O gas mixture at 680oC under thermal cyclic conditions. The hot gas composition corresponded to ac = 2.9 and an oxygen potential high enough to oxidise chromium, but not iron or nickel. All the alloys were shown to undergo internal carburisation, metal dusting and coking once the protective chromium oxide scale was damaged. Fe-25Cr was less resistant than Fe-60Cr because of its lower chromium content. However, ferritic Fe-25Cr-based steels are more resistant to dusting than austenitic Fe-25Cr-25Ni. The present findings are consistent with the earlier conclusions that cementite formation is essential for dusting on ferritic steels and that dusting of austenitic alloys does not involve the prior formation of cementite and its decomposition. The onset of metal dusting was more accelerated for most austenitic engineering alloys (Alloy 800, Inconel 601, 690, 693 and Alloy 602CA) than for engineering ferritic steels (Fe-27Cr-0.001Y). However, the alloy with the best performance was austenitic Inconel 625, which was still protected by its Cr2O3 scale after 500 one-hour cycles. In both ferritic and austenitic chromia-formers alloys, the surface ground specimens were more resistant to metal dusting than the electropolished specimens. In contrast, ferritic alumina-formers with electropolished surfaces did not dust during the entire experimental periods of 1200 one-hour cycle, but the alloys with ground surfaces slowly underwent dusting attack. The coke deposits formed consisted largely of graphite nanotubes, containing small particles at the tube tips. These particles were identified as single crystal cementite, in the case of ferritic steels, and austenite, for the austenitic alloys. This is not in agreement with the currently accepted dusting model for ferritic steels that cementite decomposition yields iron particles, which catalyse coke deposition. EDX analysis of the cementite particles, showed that the only metal detected was iron, thus differing in chemistry from the (Fe,Cr)3C surface layer. Similarly, the austenite particles contained only nickel and iron, differing in chemistry from the disintegrated alloy surfaces. These results suggested that the particles were formed in the coke in the carbon-supersaturated gas, rather than disintegration of the alloy surface layer. Strong orientation relationships were determined between the graphite and cementite particles; however, no clear crystallographic relationship was deduced between the graphite and austenite. Relative alloy performance appears consistent using the present multiple one-hour cycle and the results of others using a smaller number of lengthy cycles. Hourly thermal cycling was shown to accelerate the dusting onset for both electropolished chromia-formers and surface ground alumina-formers. Protective oxide scales spall at a critical thickness and carbon attack results when the alloy surfaces are depleted of scale-forming elements and healing becomes impossible. On this basis, analytical models were developed and used to predict the incubation periods for oxide failure and the subsequent carbon attack. Upon testing, these models were, however, found to be not qualitatively meaningful in predicting the onset of dusting observed in the present study. Gross oversimplifications involved in the model and the absence of reliable data for many parameters required for the computations prevented even an approximate quantitative prediction.

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7

Zhou, Ning. "Simulation study of directional coarsening (rafting) of [gamma]' in single crystal Ni-Al". Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1228152557.

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8

Underhill, Richard P. "The spray forming of Ni based superalloys". Thesis, University of Oxford, 1995. http://ora.ox.ac.uk/objects/uuid:a26505d4-90cf-41ff-86e9-fbf903c9a87f.

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The main aim has been to investigate the effect of process parameters on the spray forming of UDIMET 720 and in particular to understand the mechanism of grain size evolution in the deposit using a combination of experimental and computer modelling techniques. Samples of two spray formed Ni superalloys, MAR-M-002 and UDIMET 720, have been re-heated into the solid/liquid region and the fully solid region just below the solidus temperature for a series of times to try and reproduce the situation of grain growth in a spray formed deposit. Grain growth in the solid/liquid region follows the equation: d³=d₀³ +Kt, where d is the grain size, d₀ is the initial grain size, K is the coarsening rate constant and t is the time. Coarsening rate constants have been determined for temperatures in the solid/liquid region and they increase with increasing temperature/decreasing solid fraction. Existing spray forming equipment for Al alloys has been modified to manufacture UDIMET 720 deposits. Process conditions were monitored continually during spray forming, in particular the temperature of the deposit by embedded thermocouples and infra red thermal imaging of the deposit top surface. Above a deposit temperature of ≈1250°C the microstructure consists of equiaxed fine grains (20μm-35μm) and the porosity is low (<1%). Below this deposit temperature the microstructure consists of droplet "splats" and the porosity is higher (2-4%). The measure grain size increases with increasing deposit temperature and solidification time and agrees reasonably well with the predicted grain size using the above equation. A commercial finite difference based fluid dynamics software program, FLUENT, has been used to model the 2-dimensional dynamic and thermal behaviour of UDIMET 720 droplets during gas atomisation and spray forming. The effect of atomising gas pressure, spray distance and melt mass flow rate on the equilibrated droplet spray temperature has been examined and shows similar variations with process parameters as the measured maximum deposit temperature. The predicted spray temperature at the substrate is always higher than the measured maximum deposit temperatures under all conditions, and increases with (i) decreasing gas pressure, (ii) decreasing spray distance and (iii) increasing MFR. Mean droplet temperatures and velocities are strongly dependent on droplet size, the mean droplet temperature decreases and mean droplet axial velocities increases with decreasing droplet size.

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9

Eurich, Nikolai Carl. "First principles investigation of intermetallic phases and defects in Ni-base superalloys". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709196.

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10

Ibañez, Alejandro R. "Modeling creep behavior in a directionally solidified nickel base superalloy". Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04072004-180026/unrestricted/ibanez%5Falejandro%5Fr%5F200312%5Fphd.pdf.

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11

Moricca, Maria del Pilar. "High temperature oxidation characteristics of Nb-10W-XCr alloys". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.

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12

Kong, Yonghua. "Effects of minor alloying on the microstructures and creep properties of RR2086 superalloys". Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B31634047.

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13

Bowman, R. R. (Randy R. ). "Effect of microstructure on the fatigue crack growth resistance of nickel-base super alloys". Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/20022.

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14

Chen, Wei. "Composition effects on macroscopic solidification segregation of superalloys". Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1329.

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Thesis (Ph. D.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains xii, 145 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 143-145).

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15

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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16

Hosamani, Laxmappa G. "Experimental and theoretical heat transfer studies in vacuum arc remelting /". Full text open access at:, 1988. http://content.ohsu.edu/u?/etd,166.

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17

Kish, Joseph J. "Active-passive corrosion of Fe-Cr-Ni alloys in hot concentrated sulphuric acid solutions /". *McMaster only, 1999.

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18

Highsmith, Shelby Jr. "Probabilistic fatigue crack life prediction in a directionally-solidified nickel superalloy". Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/5410.

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19

Macia, Mario Luis. "The dendritic growth of γ in astroloy". Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/20165.

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20

Tabrizi, Narges. "Optimizing the microstructure of single crystal Ni-base superalloys". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708864.

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21

Talekar, Anjali S. "Oxidation behavior of Ni-base superalloys and high strength low alloy (HSLA) steels at elevated temperatures". abstract and full text PDF (UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3316371.

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22

Quintero, Soltero Oscar. "Microstructural characterization of overaged GTD-111 HP turbine buckets". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.

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23

孔永華 e Yonghua Kong. "Effects of minor alloying on the microstructures and creep properties of RR2086 superalloys". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B31634047.

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24

Collins, David Matthew. "Modelling and characterisation of the microstructure in a polycrystalline nickel-base superalloy". Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610221.

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25

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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26

Macia, Mario Luis. "A study of dendritic precipitation, grain boundary serration formation and discontinuous precipitation in nickel base superalloys". Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19645.

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27

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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28

Mathur, Harshal. "Recrystallisation in single crystal nickel-based superalloys". Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608207.

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29

Garimella, Narayana. "Multicomponent interdiffusion in austenitic Ni-, Fe-Ni-base alloys and L1₂-Ni₃Al intermetallic for high-temperature applications". Orlando, Fla. : University of Central Florida, 2009. http://purl.fcla.edu/fcla/etd/CFE0002521.

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30

Ibanez, Alejandro R. "Modeling creep behavior in a directionally solidified nickel base superalloy". Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/5353.

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31

Shi, Shu. "Repair weldability of heat-resistant stainless steel casings-HP45NB, HP50NB and 20-32NB alloys". The Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1140490923.

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32

Lundberg, Daniel, Filip Wilson, Hjalmar Gunnarsson, Leo Sjörén, Robin Xu e Erik Djurberg. "Long term aging and creep exposure for advanced heat resistant alloys : A phase analysis". Thesis, Uppsala universitet, Institutionen för materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-446407.

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This project was ordered by Sandvik Materials Technology and was performed by a group of students at Uppsala university. The purpose of the project was to study precipitation behavior and structure stability in six advanced heat resistant alloys. Each sample were subjected to a creep rupture test in 600 or 700°C depending on the alloy type. Two parts of each alloy where examined; one part which had been affected by creep and another part which was unaffected by creep. A literature study was performed first to gain knowledge of the scientific theory utilized in this project, namely creep, precipitation hardening, and about the different materials which were analyzed. Preliminary results for the phase composition of the materials were obtained from a Thermo-Calc (TC) simulation. The SEM-images showed nothing noteworthy for any sample due to the roughness of the sample surfaces. The EDS-analysis showed chromium depletion in the centers of the aged samples of HT9 and Sanicro® 75X. Other minority phases such as Cr23C6 in Sanicro®70, P-phase and a titanium nitride phase in sanicro® 60X, VB in Esshete 1250 and Sigma-phase in 4C54 were identified using EDSmapping. It was found that when using XRD to analyze the phase compositions of small samples it is impractical to have the samples cast in bakelite beforehand. The XRD-results obtained in this project showed that more than 90% of the XRD diffractogram for every sample was graphite, which made the identification of minority phases impossible. The quality of the LOM-images varied greatly between samples, for 4C54 grain sizes were measured in all images, for Esshete 1250 grain sizes were measured for the crept sample, and for Sanicro® 60X measurements could only be taken from one image. Most of the sample preparation was insufficient to achieve the test results necessary for complete microstructural analysis and phase analysis of the samples. The mistakes in the practical steps of the project were noted and improvements for these mistakes are presented in the conclusion.

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Tsutsumi, Mitsuyoshi. "FATIGUE AND CREEP FATIGUE BEHAVIOR OF HEAT RESISTANT ALLOYS WITH ANISOTROPIC AND COMPOSITE MICROSTRUCTURES". Kyoto University, 1998. http://hdl.handle.net/2433/182333.

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34

Sulaiman, Samsiah. "Structure of properties of the heat affected zone of P91 creep resistant steel". Access electronically, 2007. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20080916.150054/index.html.

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35

Shenoy, Mahesh M. "Constitutive Modeling and Life Prediction in Ni-Base Superalloys". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11515.

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Microstructural features at different scales affect the constitutive stress-strain response and the fatigue crack initiation life in Ni-base superalloys. While numerous efforts have been made in the past to experimentally characterize the effects of these features on the stress-strain response and/or the crack initiation life, there is a significant variability in the data with sometimes contradictory conclusions, in addition to the substantial costs involved in experimental testing. Computational techniques can be useful tools to better understand these effects since they are relatively inexpensive and are not restricted by the limitations in processing techniques. The effect of microstructure on the stress-strain response and the variability in fatigue life were analyzed using two Ni-base superalloys; DS GTD111 which is a directionally solidified Ni-base superalloy, and IN100 which is a polycrystalline Ni-base superalloy. Physically-based constitutive models were formulated and implemented as user material subroutines in ABAQUS using the single crystal plasticity framework which can predict the material stress-strain response with the microstructure-dependence embedded into them. The model parameters were calibrated using experimental cyclic stress-strain histories. A computational exercise was employed to quantify the influence of idealized microstructural variables on the fatigue crack initiation life. Understanding was sought regarding the most significant microstructure features using explicit modeling of the microstructure with the aim to predict the variability in fatigue crack initiation life and to guide material design for fatigue resistant microstructures. Lastly, it is noted that crystal plasticity models are often too computationally intensive if the objective is to model the macroscopic behavior of a textured or randomly oriented 3-D polycrystal in an engineering component. Homogenized constitutive models were formulated and implemented as user material subroutines in ABAQUS, which can capture the macroscale stress-strain response in both DS GTD111 and IN100. Even though the study was conducted on two specific Ni-base superalloys; DS GTD111 and IN100, the objective was to develop generic frameworks which should also be applicable to other alloy systems.

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36

Rzyankina, Ekaterina. "Numerical and experimental investigation of directional solidification in vacuum investment casting of superalloys". Thesis, Cape Peninsula University of Technology, 2013. http://hdl.handle.net/20.500.11838/1243.

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Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Mechanical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2013
High temperatures encountered in combustion chambers of jet engines has demanded the creation of new technologies and new materials for the construction of one of the most critical elements of these systems - the stator and rotor turbine blades. They have to withstand extreme temperatures for extended periods without the loss of mechanical strength, conditions under which many steels and alloys fail. Such failure is ascribed to the combination of high temperatures and high centrifugal forces, resulting in creep. The high temperature creep mechanism of grain boundary sliding has limited the operation capability of fine-grained equiaxed castings. Higher operating temperatures were achieved with higher alloy contents and coarse-grained equiaxed castings. This is especially prevalent in multi-crystalline structures in which grain boundaries present weaknesses in the structure. However, notwithstanding these improvements, high temperature resistant alloys formed as single crystal structures offer the necessary material properties for safe performance under these extreme conditions. Damage to turbine blade surfaces is often caused by oxidation and hot corrosion. For this reason, turbine blades are coated with a thermal barrier coating (TBC), which consists of ceramic materials that reduce the heat flux through the airfoil. In this research work, modelling and simulation techniques were initially used to study the directional solidification (DS) of crystal structures during vacuum investment casting. The modelling of the solidification process was implemented using a Finite Element casting simulation software, ProCAST, to predict thermal and flow profiles. These models allowed the study of the dendritic growth rate, the formation of new grains ahead of the solid/liquid interface and the morphology of the dendritic microstructure. These studies indicated the opportunity to optimise the velocity of the solidification front (solidification rate) for single crystal structures. The aim of this research was therefore to investigate the effect of the solidification rate (or withdrawal velocity) on the quality of SC castings. The investigations were carried out for nickel-based superalloy CMSX-4 turbine blade casts and rods using the Bridgman process for vacuum investment casting. The SC castings were heat treated to improve the grain structure for enhanced creep resistance. The heat treated SC castings were inspected by X-ray diffraction to analyse crystallographic orientation and chemical composition; and by SEM, OP (optical microscopy) and microprobe analysis to analyse the microstructure; in addition to macrostructural investigations. In the experimental analysis, the formation of new grains ahead of the solidi/liquid interface and the effect of dendrite packing patterns on the primary dendrite spacing were investigated. Creep tests were conducted to compare the creep properties of the SC castings for different withdrawal rates, and to draw conclusions regarding the effect of withdrawal rate on the microstructure (and hence the creep properties) of SC castings.

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de, Bussac Arnaud. "A study of deformation and fatigue in model Ni-base superalloys". Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/20174.

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Papangelakis, V. G. (Vladimiros George) 1958. "Aqueous pressure oxidation of arsenopyrite". Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65435.

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39

Leyland, Steven Paul. "Casting of single crystal nickel superalloys with reactive elements". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709416.

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40

Priest, Matthew. "Synthesis of reactive element-modified aluminide coatings on single-crystal Ni-based superalloys by a pack cementation process a thesis presented to the faculty of the Graduate School, Tennessee Technological University /". Click to access online, 2009. http://proquest.umi.com/pqdweb?index=26&did=1760523421&SrchMode=1&sid=1&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1254926883&clientId=28564.

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41

Ventura, Julieta Angelica. "High temperature oxidation behavior of Nb-20Mo-15Si-5B-20Cr alloy". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.

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42

Bradley, Christopher Michael. "Microstructural characterization and heat treatment of A-286 turbine buckets". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.

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43

Rajamure, Ravi Shanker. "Laser Surface Alloying of Refractory Metals on Aluminum for Enhanced Corrosion Resistance: Experimental and Computational Approaches". Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc700029/.

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Aluminum (Al) and its alloys are widely used in various technological applications, mainly due to the excellent thermal conductivity, non-magnetic, ecofriendly, easy formability and good recyclability. However due to the inferior corrosion resistance its applications are hampered in various engineering sectors. Besides, the corrosion related failures such as leakage of gas from pipeline, catastrophic breakdown of bridges and fire accidents in processing plants further puts the human life in jeopardy. Within the United States over $ 400 billion dollars per year are spent over research to understand and prevent the corrosion related failures. Recently, the development of transition metal(TM) aluminides (AlxTMy, where, TM = Mo, W, Ta, Nb, Cr, Zr and V) has received the global attention mainly due to high strength at elevated temperatures, light-weight, excellent corrosion and wear resistance. In light of this, surface modification via laser surface alloying (LSA) is a promising engineering approach to mitigate the corrosion and wear problems. In the present study the attempts are made to study the Al-Mo, Al-W, Al-Nb, and Al-Ta systems as a potential corrosion resistant coatings on aluminum. The refractory metal (Mo, W, Nb, Ta) precursor deposit was spray coated separately on aluminum substrate and was subsequently surface alloyed using a continuous wave diode-pumped ytterbium laser at varying laser energy densities. Microstructural analysis was conducted using scanning electron microscopy and further X-ray diffractometry was carried out to evaluate the various phases evolved during laser surface alloying. Corrosion resistance of laser alloyed coatings were evaluated using open circuit potential, cyclic potentiodynamic polarization, electrochemical impedance spectroscopy measurements were performed in 0.6 M NaCl solution (pH:6.9±0.2, 23˚C). Open circuit potential measurements indicate the more stable (steady state) potential values over long periods after laser surface alloying. Cyclic polarization results indicated reduction in the corrosion current density, enhancement in the polarization resistance, and increase in coating/protective efficiency with increase in laser energy density compared to untreated aluminum. Electrochemical impedance spectroscopy measurements also indicated an increase in charge transfer resistance after laser surface alloying of refractory metals on aluminum. Additionally, first principle calculations of thermodynamic, electronic and elastic properties of intermetallics evolved during LSA were also thoroughly investigated to correlate the corrosion performance of intermetallic coatings with these properties. The present study indicates that novel Al-Mo, Al-W, Al-Nb, and Al-Ta intermetallics has a great potential for light weight structural applications with enhanced corrosion resistance.

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Amaro, Robert L. "Thermomechanical fatigue crack formation in a single crystal Ni-base superalloy". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/37172.

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This research establishes a physics-based life determination model for the second generation single crystal superalloy PWA 1484 experiencing out-of-phase thermomechanical fatigue (TMF). The life model was developed as a result of a combination of critical mechanical tests, dominant damage characterization and utilization of well-established literature. The resulting life model improves life prediction over currently employed methods and provides for extrapolation into yet unutilized operating regimes. Particularly, the proposed deformation model accounts for the materials' coupled fatigue-environment-microstructure response to TMF loading. Because the proposed model is be based upon the underlying deformation physics, the model is robust enough to be easily modified for other single crystal superalloys having similar microstructure. Future use of this model for turbine life estimation calculations would be based upon the actual deformation experienced by the turbine blade, thereby enabling turbine maintenance scheduling based upon on a "retirement for a cause" life management scheme rather than the currently employed "safe-life" calculations. This advancement has the ability to greatly reduce maintenance costs to the turbine end-user since turbine blades would be removed from service for practical and justifiable reasons. Additionally this work will enable a rethinking of the warranty period, thereby decreasing warranty related replacements. Finally, this research provides a more thorough understanding of the deformation mechanisms present in loading situations that combine fatigue-environment-microstructure effects.

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Dzebo, Sead. "Investigation of methods to improve process performance in centerless grinding of Inconel 718 and Ti-6Al-4V superalloys". Thesis, Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/37113.

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Grinding is an abrasive machining process used for the final shaping of components that require very smooth surfaces and a high dimensional accuracy. In recent years, the costs of industrial grinding operations have increased with a greater demand for high-strength, low-weight superalloy components. Titanium and nickel-based alloys are desirable for their high creep-rupture strength and corrosion and oxidation resistance in high-temperature environments. However, they are very difficult to grinding due to a combination of poor thermal properties, rapid work-hardening, and a high level of chemical reactivity. In this thesis, two methods are investigated to improve process performance in plunge centerless grinding of Inconel 718 and Ti-6Al-4V superalloy fasteners: (i) economic optimization of grinding process parameters and (ii) reduced quantity lubrication using a graphite nanoplatelet-enhanced grinding fluid. In the first part, a systematic methodology is presented for finding the optimum parameters in two stages: (i) modeling of process and part quality constraints, and (ii) determination of optimum grinding conditions in the feasible operating region. In the second part, the performance of a graphite nanoplatelet-enhanced grinding fluid in reduced quantity lubrication centerless grinding is evaluated to assess its potential as a cost-effective alternative to the traditional flood cooling method. The results of the study indicate that an appreciable reduction in the cost of the superalloy grinding operation can be achieved by operating at the optimum parameters. In addition, it is shown that the application of a graphite-enhanced fluid at a reduced flow rate is more effective than high-volume flood cooling in reducing specific grinding energy levels and wheel wear rates, thus offering the potential to increase process productivity.

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Callender, Chad M. "Refractory metal to nickel-based alloy joining technologies for high temperature applications". Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Summer/Theses/CALLENDER_CHAD_35.pdf.

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47

Godfrey, A. W. "Some studies of the effect of directional recrystallisation on the properties of a powder metallurgy superalloy". Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670275.

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48

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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Abstract (sommario):

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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Marinescu, Iulian. "Investigation of monitoring techniques for the detection of tool/workpiece malfunctions in milling of heat resistant alloys". Thesis, University of Nottingham, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.537638.

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50

Whelchel, Ricky Lee. "Characterization of a nickel-base superalloy through electrical resistivity-microstructure relationships facilitated by small angle scattering". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41130.

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Abstract (sommario):

Nickel-base superalloys obtain high temperature mechanical properties through formation of precipitate phases formed via heat treatment. The precipitate microstructure evolves with heat treatment or thermal exposure, which can lead to degrading mechanical properties. This project focuses on the use of electrical resistivity as a non-destructive testing method to monitor the precipitate phase in Waspaloy (a polycrystalline nickel-base superalloy). The evolution of the precipitate microstructure is characterized throughout the volume of the specimens using both small angle neutron scattering (SANS) and ultra small angle X-ray scattering (USAXS) measurements. These measurements are also aided by microscopy and X-ray diffraction measurements.

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