3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Phase equilibrium diagram of Co-Fe-Pd(2019) Ukabhai, Kiyaasha DyalThere is potential to use Co-Fe-Pd rare earth-doped alloys for magnets. The system offers possible alternatives for the heavy and expensive rare-earth magnets. The phase diagram of Co-Fe-Pd was derived nearly sixty years ago and is inconsistent. Therefore, the system needs to be studied again to provide an accurate and updated phase diagram to facilitate the development of the potential magnetic alloys. Samples of different compositions of Co-Fe-Pd were made in a button arc furnace, under an argon atmosphere on a water-cooled copper hearth. They were sectioned and part was kept in the as-cast state and the other part annealed. The samples were analysed in a scanning electron microscope with energy dispersive X-ray spectroscopy to observe the microstructures and to determine the overall and phase compositions. Samples were also analysed in an X-ray diffractometer to confirm the phases. The same analysis procedure was followed for the as-cast and the annealed samples. Coring occurred in many samples, which was expected due to the wide solid solutions in the system. The microstructures were not similar to any of the previous work. There was better agreement of the as-cast samples with the assessed 25°C isothermal section of Raghavan [1992Rag], than with the experimental one of Kuprina and Grigorev [1961Kup]. The deduced liquidus slope agreed with both of the liquidus surfaces published. Some of the phases were too fine to be analysed in the as-cast samples. It was expected that annealing the samples would have coarsened the grains, but the phases were still to fine to analyse. The 1000°C alloys were not homogenous and apart from three alloys which had two phases, the others comprised only one phase. The FePd and FePd3 regions of the Fe-Pd binary diagram did not extend perceptibly into the ternary system. The 1000°C isothermal section was comprised mainly of the A1 (γFe, αCo, Pd) phase. The samples were also annealed at 650°C. The ordered α’ peaks were difficult to identify by XRD, and FePd and FePd3 were difficult to distinguish from A1 (γFe, αCo, Pd). There was a A1 (γFe, αCo, Pd) miscibility gap in the system, around Co71:Fe16:Pd13 – Co31:Fe22:Pd47. The hardness of the alloys increased with increased Fe and decreased Pd contents. The three conditions followed the same trends for hardnesses.Item Investigation of the C-Ni-V ternary phase diagram and development of an optimum wear resistant alloy(2018) Fabuyide, Abosede AdefunkeThe C-Ni-V ternary phase diagram was investigated. The eutectics of ten as-cast samples produced by Apata [2014Apa1] were re-analysed. The results obtained were compared with previous analyses by Apata [2014Apa1] and Muobeleni [2013Muo]. The differences in eutectic analyses were identified. Six new samples were produced and analysed in the as-cast condition, as well as after annealing at 1000°C for 1000hours and water quenched. The phases in the alloys were identified using SEM-EDX, EPMA and XRD. The solidification projection of the new samples was constructed and the extensions of the binary phases were determined. A new liquidus projection was derived using results of the new samples and Apata’s [2014Apa1] samples and four ternary invariant reactions were identified, L + ~VC + βV2C → σ′, L + βV2C → σ′ + (V), L + ~VC + σ′ → (Ni) and L + ~VC → (Ni) + C, of which were slightly different from Apata [2014Apa1] and Muobeleni [2013Muo]. The isothermal section of the new sample at 1000°C was plotted Six VC-Ni alloys (from VC and Ni powders) and seven V-C-Ni alloys (from VC, V and Ni powders) were produced by spark plasma sintering. The sintered density, hardness, fracture toughness, wear performance and corrosion performance in 1M H2SO4 and 3.5wt% NaCl environments of the alloys were evaluated. Alloys with 10 at.% Ni had the preferred combination of properties, and Alloy V48:C42:Ni10 (at.%) was the optimum alloy with the following properties: 97.6% sintered density, wear rate of 3.03 ± 0.00(1) 10-6 mm3/Nm against a Si3N4 ball, corrosion rates of 0.0176mm/y in 1M H2SO4 environment, and 0.00295mm/y in 3.5wt% NaCl environment.Item An investigation of the C-Ni-V ternary phase diagram and development of abrasion-resistant alloys(2016) Apata, Ayodeji OluwatoyinThis study investigated the C-Ni-V ternary phase diagram and identification of possible abrasive-resistance alloys. Twenty-four alloys were made from the elemental components and were arc-melted under an argon atmosphere, using Ti as an oxygen-getter. These alloys were analysed in both the as-cast condition, and after annealing for 1000oC and water quenching. Microstructural characterization was carried out in a SEM with EDX, and was done to confirm the phases. The results were used to plot a solidification projection and all binary phases extended into ternary, except for ~Ni8V, ~NiV3 and ~V2C which were not found, due to the sample compositions chosen. The extensions of the binary phases were: ~Ni3V: ~15 at.% C; ~Ni2V: ~20 at.% C; σ′: ~18 at.% C; (Ni): ~27 at.% C; ~V8C7: ~2 at.% Ni; ~V6C5: ~2 at.% Ni and ~VC: ~2 at.% Ni. The liquidus surface was derived, and three ternary invariant reactions were identified. The isothermal section at 1000oC was also constructed. Hardness of the alloys was studied in both conditions. Alloys with (Ni) (188-402HV5) were found to be ductile with low hardness. Alloys containing (V), ~Ni3V and ~Ni2V were identified as hard phases (533-1052 HV5). Alloys with σ′ phase were very hard (1065-1266 HV5) extremely brittle with cracks. Fracture toughness of the C-Ni-V alloys 0.9-5.2 (MPa.m-1/2) were comparable with ceramics 0.5-5.3(MPa.m-1/2). The wear behaviour of the alloys was characterized by sliding the carbide alloys against a Cr-steel ball in a pin-on-disc configuration. There were several co-existing wear mechanisms: abrasion, adhesion and the formation of a thin tribolayers. The wear coefficients for a 10N contact load after a sliding wear path of 300m varied between 0.1 x 10-6and 7.6 x 10-6(mm3/Nm), which was not as good as WC-Co hard metals, but close.Item The behaviour of PT-based alloys at high temperature(2009-03-27T10:00:03Z) Tshawe, WendyPreviously published work on the development of the Pt-based superalloys for high temperature and special applications, as well as phase equilibria work, showed that there were problems and uncertainties with the available Pt-Al phase diagram. The aim of the current work was to make a comprehensive study of all relevant phases, and to clarify the phase boundaries of the phases: (Pt), Pt3Al (all temperature versions), Pt2Al (both phases), and Pt5Al3, by use of higher resolution SEM and XRD. A displacive transformation was confirmed for cubic Pt3Al to tetragonal Pt3Al and from high temperature Pt2Al to low temperature Pt2Al. The -phase was observed to be present, the phase reactions were confirmed and the eutectic composition was found. The Pt6Al21 phase was identified instead of Pt5Al21, and was deduced to be a different interpretation of the same phase, although the former had been described as a metastable phase. The phases and phase boundaries were found to generally agree with Massalski, and disagreed with Oya et al. ’s phase diagram