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A study has been made of the elasticity associated with the martensite transformation in the polycrystalline β-phase alloy of composition Cu-33.6 wt. % Zn-4 wt. % Sn tested at room temperature. The mechanical properties of the material undergoing the stress induced martensite transformation have been examined. These properties are influenced by the elastic anisotropy of the bcc β-phase, the development, preferential distribution and morphology and the mechanical properties of the transformation product. The elastic shape change associated with the elastically accommodated, stress-induced martensitic transformation was always found to be accompanied by some plastic deformation. A relationship between the β-grain size, the sample thickness and the deformation response was observed. Specimens with grains extending through the sample thickness exhibited large reversible strains (∼2.5%), whereas specimens with a much smaller grain size/thickness ratio (<1) exhibited only limited transformation elasticity. The morphology of the thermal martensite and the Ms temperature was also found to be influenced by the ratio grain size/thickness (g.s./t). A lower Ms temperature was associated with a decreasing g.s./t ratio; only self-accommodating burst martensite was observed in very fine grained material. The Af temperature increased with a decreasing g.s./t ratio. Repeated loading (cycling) reduced the hysteresis of the stress strain curve for all g.s./t ratios tested, but was always accompanied by plastic deformation of the matrix and the development of non-reversible deformation martensite. The experimentally determined habit plane for the thermal and the stress induced martensite were in moderate agreement with the planes predicted by the phenomenological martensite theory (W.L.R.) assuming a {110} <1Ī0> microscopic shear. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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Dissertation submitted to the faculty of Engineeung, University if the Witwatersrand, Johannesburg. in fulfilment of the requirements for the degree of Master of Science in Engineering. / This dissertation deals with alloys containing between 0.2 and 9.5wt%, carbon and between 3.2 and 64.3wt% vanadium with the balance iron. Alloys were produced by induction melting and followed by remelting in vacuum tungsten arc furnaces. No heat-treatment was performed, as the aim was to identify useful alloys that may be applied by hardfacing techniques in the field. The requirement of post weld heat-treatment would greatly limi~ the use af hardfacing alloys. TIle experimental techniques aimed at characterising the alloys included X-ray diffraction analyses, Mosshauer Spectroscopy, optical, scanning and transmission electron microscopy and chemical analyses white density measurements, hardness tests and 2 and 3 -body abrasion test gave the material properties. (Abbreviation abstract) / AC 2018

A Dissertation Submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, for the degree of Master of Science in Engineering. 1978

Thesis advisor: Zhifeng Ren / SiGe alloys are the only proven thermoelectric materials in power generation devices operating above 600 °C and up to 1000 °C in heat conversion into electricity using a radioisotope as the heat source. In addition to radioisotope applications, SiGe thermoelectric materials have many other potential applications, for example, solar thermal to electricity energy conversion and waste heat recovery. However, traditional SiGe alloy material shows low ZT values of about 0.93 at 900 °C, thus, 8% is the highest device efficiency for commercial SiGe thermoelectric devices. Recently, many efforts have been made to enhance the dimensionless thermoelectric figure-of-merit (ZT) of SiGe alloys. Among them, the nano approach has been recognized as an effective mechanism to obtain thermoelectric materials with good performance. In this approach, dense bulk samples with random nanostructures with high interface densities are synthesized through ball milling and a direct current hot press, leading to an enhancement ZT through reduced phonon thermal conductivity. Such a practical technique produced samples of nanostructured p-type dense bulk bismuth antimony telluride with a peak ZT of 1.4 at 1000 °C from either alloy ingot or elemental chunks. However, the generality of this approach has not been demonstrated. Here, we applied the same technique in SiGe system in order to fabricate a nanostructured n-type SiGe alloy with enhanced thermoelectric properties. In this thesis, numerous nanostructured n-type SiGe alloy samples were successfully pressed. The structure of these nanostructured samples was investigated via XRD, EDS, and TEM. It has been confirmed that many nano grains exist in our nanostructured samples. / Thesis (PhD) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

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