AISI 430 ferritic stainless steel (FSS) is the most widely used FSS alloy due to good resistance to stress corrosion cracking. Owing to the chemical composition range, AISI 430 alloys undergo a partial phase transformation of ferrite to austenite when subjected to hot rolling temperatures. Consequently, the alloys consist of ferrite and austenite during processing. The presence of austenite and ferrite influences the microstructure evolution and texture development during hot rolling and subsequent annealing heat treatments. Two AISI 430 FSS heats of varying austenite volume fraction were used in this study. The two AISI 430 FSS heats were deformed using the first three passes of the Steckel mill hot rolling process. Post deformation heat treatments namely: continuous phase transformation and martensite tempering heat treatments were performed after three successive simulated Steckel mill passes. Microstructure analyses were performed using light microscopy and Electron Backscattered Diffraction (EBSD). The microstructure analyses were performed in order to determine microstructure evolution and texture development during hot deformation and post deformation heat treatments. The difference in austenite volume fraction in the respective heats A and B has profound influence on the possibilities for microstructure and texture evolution. For the higher austenite volume fraction heat A, the post-deformation path for austenite decomposition can lead to two very different textures in the prior austenite regions. During continuous diffusional transformation from austenite to ferrite the final texture is influenced by expected variant selection as well as growth selection during the prolonged isothermal heat treatment. The result is relatively strong {001}<110> texture and comparably very weak γ-fiber texture. In the case of the martensite tempering process the γ-fiber texture that is inherited from the austenite to martensite diffusionless transformation is maintained in the prior austenite regions. The mode of post-deformation heat treatment does not significantly impact on texture development in heat B where the texture is dominated by recovery and growth in the primary ferrite phase.

Includes bibliographical references (leaves 97-101) / Two routes of Oxygen Diffusion Hardening (ODH) have been investigated on two alloys of titanium, Ti-6AI-4V and Ti-6AI-7Nb (by weight). The first route involves a controlled atmosphere where argon saturated with water was used to transport water into the test pieces at elevated temperatures. The controlled atmosphere would encourage the generation of mono-atomic oxygen through the dissociation of water vapour, and therefore change the kinetics of physical absorption and diffusion of oxygen into titanium. The second route of ODH investigated was the Oxygen Boost Diffusion Hardening (OBDH). The oxygen boost diffusion hardening process was carried out in two steps. The first step was oxidation of the samples in air at elevated temperatures and the second step was to further diffusion treat the pre-oxidised test pieces III a vacuum or argon. Various temperature and time combinations were used on both steps of OBDH.The results revealed that the ODH heat-treatment in a controlled saturated argon environment was unsuccessful in developing a significant oxygen diffusion hardened layer. The OBDH process can be carried out to modify the surface properties of titanium and alloys. Both steps of this process play a vital role in achieving a thick modified layer for improved tribological properties of titanium and alloys. Performing the oxidation step of OBDH heat-treatment at higher temperatures results in higher surface hardness and deeper diffusion zone than carrying the oxidation step at lower temperatures for longer times provided there is no peeling of the oxide scale during the high temperature oxidation. The Ti-6AI-4V achieves higher surface hardness than the Ti-6AI-7Nb upon the same OBDH heat-treatment. The second step of the OBDH can also be carried out in an argon environment instead of vacuum. Carrying out the second step in an argon atmosphere allowed for higher surface hardness and thicker hardened zone than carrying the same step in vacuum. The effect of the OBDH on the underlying microstructures of two alloys under investigation is the depletion of the ɑ phase on the modified surface as a result of the diffused oxygen which stabilises the ɑ phase. Although higher surface hardness was achieved for the Ti-6AI-4V alloy than the Ti-6AI-7Nb alloy after the same heat treatment, the Ti-6AI-7Nb alloy achieved higher wear resistance due to more adherence of the oxide scale after the oxidation step. Despite achieving higher surface hardness and thicker hardened zone upon carrying out the second step of OBDH in an argon atmosphere than in vacuum, samples which underwent the second step of OBDH heat-treatment in vacuum exhibited higher wear resistance. Performing a twin cycle OBDH heat-treatment results in even higher surface hardness and higher wear resistance despite the severe scaling of the alloys upon the heat treatments.

Includes bibliographical references (p. 421-429).

Includes abstract. Includes bibliographical references.

<p>With the world of technology constantly advancing, there will always be a need to improve the source of energy providing the power in a number of applications.<br />Supercapacitors, specifically, have become important power components for cell phones, laptops, and, more recently, electric and hybrid vehicles. In order to increase the efficiency ofsupercapacitors, novel structures must be investigated to increase surface area, which is one key to the energy storage mechanism of supercapacitors. By<br />infiltrating the open cells of high porosity nickel foam with sintered filamentary nickel<br />plaque, a unique, high surface area structure with high porosity has been produced. The mechanical properties of the resulting structure are a compromise of the two constituents; nickel foam and nickel plaque. The nickel foam provides ductility, and the nickel plaque provides strength and stiffuess, with a final composite structure that averages a yield strength of 1.87 MPa, a UTS of 2.25 MPa, an elastic Modulus of 515 MPa, and an average percent elongation of 7.6%. As the relative density of the composite increases, the strength and modulus both increase, while the percent elongation decreases. This high surface area, high porosity material could serve as a viable substrate for a thin coating, which would provide the electrical properties of a supercapacitor.</p> / Master of Applied Science (MASc)

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