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The aim of this study was to investigate a zirconia-matrix reinforced with metal powder (chromium, iron and stainless steel (AISI 316)) including processing, characterisation, and measurements of their properties (mechanical, thermal and electrical). Zirconia stabilised with 5.4 wt% Y₂0₃ (3 mol%) as the matrix was first studied and followed by an investigation of the effects of metal reinforcement on zirconia-matrix composites. Monolithic zirconia was pressureless sintered in air and argon to observe the effect of sintering atmosphere, while the composites were pressureless sintered in argon to avoid oxidation. Sintering was carried out at various temperatures for 1 hour and 1450°C was chosen to get almost fully dense samples. The density of the fired samples was measured using a mercury balance method and the densification behaviour was analysed using TMA (Thermo-mechanical Analysis). The TMA was also used to measure the coefficient of thermal expansion. In addition, thermal analysis using DTA and TGA was performed to observe reactions and phase transformations. Moreover, optical microscopy and SEM were used to observe the microstructures, XRD was used for phase identification, and mechanical properties including Vickers hardness, fracture toughness and bending strength were measured. The effect of thermal expansion mismatch on thermal stresses was also analysed and discussed. Finally, thermal diffusivity at room temperature and as a function of temperature was measured using a laser flash method, and to complete the study, electrical conductivity at room temperature was also measured. The investigation of monolithic zirconia showed that there was no significant effect of air and argon atmosphere during sintering on density, densification behaviour, microstructures, and properties (mechanical and thermal). Furthermore, the results were in good agreement with that reported by previous researchers. However, the presence of metal in the composites influenced the sintering behaviour and the densification process depends on the metal stability, reactivity, impurity, particle size, and volume fraction. Iron reacted with yttria (zirconia stabiliser), melted and reduced the densification temperature of monolithic zirconia, while chromium and AISI 316 did not significantly affect the densification temperature and did not react with either zirconia or yttria. AISI 316 melted during fabrication. Moreover, all of the metal reinforcements reduced the final shrinkage of monolithic zirconia. In terms of properties, the composites showed an increase in fracture toughness, and a reduction in Vickers hardness and strength with increasing reinforcement content. In addition, the thermal diffusivity of the composites showed an increase with reinforcement content for the zirconia/chromium and zirconia/iron composites, but not for the zirconia/AISI 316 composites due to intrinsic mircocracking. Furthermore, all the composites became electrically conductive with 20 vol% or more of reinforcement. It has been concluded that of those composites the zirconia/chromium system may be considered as having the best combination of properties and although further development is needed for such composites to be used in real applications in structural engineering, the materials may be developed based on these findings. In addition, these findings may be used in development of ceramic/metal joining as composite interlayers are frequently used.

Chong, Kam Cheong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references. / Text in English; abstract also in Chinese. / Chong, Kam Cheong. / ACKNOWLEDGMENT --- p.i / ABSTRACT --- p.ii / 摘要 --- p.iv / Table of contents --- p.v / Chapter 1 --- Introduction / Chapter 1.1 --- Metal Matrix Composites / Chapter 1.1.1 --- Background --- p.1-1 / Chapter 1.1.2 --- Some metallic matrix materials --- p.1-2 / Chapter 1.1.2.1 --- Aluminum alloys --- p.1-2 / Chapter 1.1.2.2 --- Titanium alloys --- p.1-3 / Chapter 1.1.3 --- Different kinds of reinforcements --- p.1-3 / Chapter 1.2 --- Conventional fabrication Methods --- p.1-5 / Chapter 1.2.1 --- Primary liquid phase processing --- p.1-5 / Chapter 1.2.1.1 --- Squeeze casting --- p.1-5 / Chapter 1.2.1.2 --- Spray deposition --- p.1-5 / Chapter 1.2.1.3 --- Slurry casting --- p.1-5 / Chapter 1.2.1.4 --- In Situ processing --- p.1-6 / Chapter 1.2.2 --- Primary solid state processing --- p.1-6 / Chapter 1.2.2.1 --- Physical vapour deposition (PVD) --- p.1-6 / Chapter 1.2.2.2 --- Powder blending and sintering --- p.1-7 / Figures for chapter 1 --- p.1-9 / Tables for chapter 1 --- p.1-14 / References --- p.1-15 / Chapter 2 --- Powder metallurgy --- p.2-1 / Chapter 2.1 --- Introduction --- p.2-1 / Chapter 2.2 --- Fabrication of metal matrix-particulate composites --- p.2-2 / Chapter 2.3 --- Our motivation --- p.2-4 / Figures for chapter 2 --- p.2-5 / References --- p.2-7 / Chapter 3 --- Effects of sintering in processing of metal matrix composites --- p.3-1 / Chapter 3.1 --- Introduction of sintering processing --- p.3-1 / Chapter 3.1.1 --- Solid state sintering --- p.3-2 / Chapter 3.1.2 --- Liquid state sintering --- p.3-5 / Chapter 3.1.3 --- Sintering in metal matrix composites(reactive sintering) --- p.3-7 / Figures for chapter 3 --- p.3-11 / Reference --- p.3-14 / Chapter 4 --- Experiments --- p.4-1 / Chapter 4.1 --- Introduction --- p.4-1 / Chapter 4.2 --- Methodology --- p.4-3 / Chapter 4.2.1 --- High temperature furnace experiment --- p.4.3 / Chapter 4.2.2 --- Arc-melting furnace experiment --- p.4-4 / Chapter 4.3 --- Sample preparations --- p.4-4 / Chapter 4.3.1 --- Sample requirements --- p.4-4 / Chapter 4.3.2 --- Sample milling --- p.4-6 / Chapter 4.3.3 --- Cold pressing --- p.4-6 / Chapter 4.3.4 --- Annealing conditions for high-temperature furnace --- p.4-7 / Chapter 4.3.4.1 --- Different sintering temperatures --- p.4-7 / Chapter 4.3.4.2 --- Different sintering duration --- p.4-8 / Chapter 4.3.5 --- Sample conditions in arc-melting furnace --- p.4-8 / Chapter 4.4 --- Instrumentation --- p.4-10 / Chapter 4.4.1 --- Arc-melting furnace --- p.4-10 / Chapter 4.4.2 --- Vickers hardness tester --- p.4-11 / Chapter 4.4.3 --- X-Ray powder diffractometer (XPD) --- p.4-13 / Chapter 4.4.4 --- Scanning electron microscopy & energy dispersive x-ray analysis --- p.4-15 / References --- p.4-18 / Chapter 5 --- Results / Chapter 5.1 --- High-temperature furnace --- p.5-1 / Chapter 5.1.1 --- XPD results --- p.5-1 / Chapter 5.1.2 --- Different sintering temperatures in 10 weight percent of Cr203 - A1 samples with 1 hour sintering time --- p.5-2 / Chapter 5.1.3 --- Different sintering temperatures in 15 weight percent of Cr203 一 A1 samples with 1 hour sintering time --- p.5-6 / Chapter 5.1.4 --- Different sintering temperatures in 20 weight percent of Cr203 ´ؤ A1 samples with 1 hour sintering time --- p.5-10 / Chapter 5.1.5 --- Different sintering temperatures in 30 weight percent of Cr203 ´ؤ A1 samples with 1 hour sintering time --- p.5-13 / Chapter 5.1.6 --- Different sintering time for 10 weight percent of Cr203 ´ؤ A1 samples at 1100°C sintering temperature --- p.5-19 / Chapter 5.1.7 --- Different sintering time for 15 weight percent of Cr203 ´ؤ A1 samples at 1100°C sintering temperature --- p.5-21 / Chapter 5.2 --- Arc-melting furnace --- p.5-24 / Chapter 5.2.1 --- XPD results --- p.5-24 / Chapter 5.2.2 --- Samples that were melted in arc-melting furnace --- p.5-25 / Chapter 5.2.3 --- Powder samples that were melted in arc-melting furnace --- p.5-28 / Figures for chapter 5 --- p.5-30 / References --- p.5-55 / Chapter 6 --- Discussions --- p.6-1 / Chapter 6.1 --- Chemical reactions --- p.6-1 / Chapter 6.2 --- Sintering --- p.6-6 / Chapter 6.2.1 --- Conditions for having larger Al13Cr2 intermetallic compound --- p.5-7 / Chapter 6.3 --- Vickers hardness results --- p.6-10 / Chapter 6.4 --- Comparisons between the two furnace results --- p.6-12 / Chapter 6.4.1 --- Cooling rates --- p.6-12 / Chapter 6.4.2 --- Volume fraction of all the intermetallic compounds --- p.6-14 / Chapter 6.4.3 --- Pore sizes --- p.6-15 / Chapter 6.4.4 --- Vickers hardness --- p.6-16 / References --- p.6-17 / Chapter 7 --- Conclusions and suggestions for further studies --- p.7-1 / BIBLIOGRAPHY

Thesis (M.S.)--Drexel University, 2003. / Includes abstract. Includes bibliographical references (leaves 57-59).

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: powder metallurgy; density distribution; compaction modeling; compact; powder; compaction. Includes bibliographical references (p. 141-142).

Nickel-based Superalloys are widely used in the steam turbine power generation and aerospace industries. They possess the desirable qualities of high-temperature strength, oxidation and corrosion resistance and can operate in some of the highest temperature ranges of the structural metals. The oxidation resistance of a Superalloy is achieved primarily through the formation of a dense alumina and/or chromia oxide layer(s) including spinels. This resistance has been further improved in wrought and cast alloys through the addition of reactive elements such as silicon, yttrium and lanthanum, although the exact effects of these elements have not been well defined. This project concentrated on a powder metallurgy ternary master alloy consisting of Ni-12Cr-9Fe (w/o) with additions of 6w/o aluminum, 0.5w/o Si, and 0.1w/o Y, in various combinations. Specifically, the primary goal was to produce and characterize a PM manufactured nickel-based Superalloy with minor additions of reactive elements and to assess the effectiveness of the Si and/or Y in improving the oxidation resistance. JMatPro modeling software was first used to help determine temperatures at which various events would occur in the alloys such as solutionizing and liquation temperatures. Subsequently green compacts were produced by a press (uni-axially) and sinter route to create transverse rupture strength bars (TRS bars). These bars were then thermomechanically deformed using a Gleeble tester to reduce porosity followed by a heat treatment to restore a microstructure better suited for high temperature oxidation. Sectioned TRS bars were then oxidized (static) 900?C in air for times up to 1000h and the influence of the Si/Y additions on oxidation resistance was determined via a combination of weight gain data and microstructural examination. Whereas JMatPro predicted solutionizing temperature of the compositions studied (1010°C quaternary; 1020°C quaternary + Si, respectively) these values were slightly lower than the results observed through DSC experiments (1045°C quaternary; 1065°C quaternary + Si, respectively). A w/o ?’ of approximately 25% was predicted by the modeling tool, but values of 58.3% to 61.7% were determined using a point count method. Finally, the addition of 0.5w/o Si to the quaternary Ni-Cr-Fe-Al PM system provided a measureable improvement in the oxidation resistance both in terms of thickness of oxide layer and in overall weight gain. Conversely, 0.1w/o Y provided little benefit, and was shown to be detrimental to alloys not containing Si.

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