Includes abstract. / Includes bibliographical references. / The purpose of this thesis was to explore the suitability for Rammed Earth construction in the Cape Town metropolitan area. This would ultimately lead to drawing up a guideline for building of Rammed Earth housing and structures. The research involved collecting sixteen soil samples from strategically selected sites in Cape Town. The suitability of a soil was established through a variety of tests, varying between relatively simple field tests and rigorous laboratory analysis. These tests were undertaken to assess soil grading, organic matter content, plasticity and Optimum Moisture Content (OMC). Grading gave an indication of fines present and plasticity indicated the cohesive nature of the fines. More detailed tests were undertaken to determine type and level of soluble salts and mineralogical composition.

Includes bibliographical references. / The Cr-Pt system has been extensively studied in recent decades with the aim of providing a reliable thermodynamic description of the phases shown in the equilibrium phase diagram. The Cr-Pt coated system where Pt layers were deposited onto Cr substrates is investigated in this study with particular interest in the formation of Cr-Pt phases and coating morphology as a function of coating thickness and heat treatment parameters (temperature and time). The main aim of this research was to produce the coated system with properties which can be tailored according to the conditions required by their particular application. The system was investigated using several complementary techniques.

Includes bibliographical references. / The use of galvanised coatings on steel for structural ropes, bundles and wires has become standard practice as unprotected steel is prone to corrosion degradation. Galvanised coatings increase the service lifespan of steel by providing barrier and cathodic corrosion protection. Zinc (Zn) and zinc-aluminium (Zn-Al) alloys are the most commonly used metallic coatings on steel wire. Zn-Al coatings outperform Zn coatings, most notably in marine environments, as they combine the highly insulating oxide film associated with Al corrosion and the cathodic protection of Zn to the underlying steel.

Includes bibliographical references. / Phase transformations in Pt-V coatings after heat treatment have been investigated. Five Pt- V ordered phases (PtV, PtV 3 , Pt 2 V, Pt 3 V and Pt 8 V) have been previously observed in bulk platinum-vanadium alloys. Phase formation in coatings is expected to be sequential and controlled by the lowest temperature eutectic (liquidus) composition; this allows control of experimental parameters for formation of desired ordered phases. This investigation included fabrication of coatings, heat treatments, morphology characterization and phase analysis. Single and multilayer coatings ranging between 0.07 μm and 0.5 μm were deposited on vanadium and platinum substrates using E-beam deposition. The kinetics of phase transformation were studied by subjecting the coated layers to a variety of heat treatments in the temperature range 600°C to 900°C for 4 and 8 hours. Composition and morphology characterization was carried out using EDS and SEM respectively. XRD was used for phase analysis. Four (PtV, PtV 3 , Pt 2 V, Pt 3 V) out of the five Pt-V ordered phases exhibited in bulk alloys, were successfully formed from the coating system investigated in this project. The first phase formed, and the sequence of phase formation, was found to be different depending on which metal formed the substrate. The vanadium-rich ordered phase (PtV 3 ) was preferentially formed first on vanadium substrates and the sequence of phase formation progressed through ordered phases richer in platinum. The platinum-rich ordered phase (Pt 3 V) was preferentially formed first on platinum substrates and the sequence continued towards formation of ordered phases richer in vanadium. An increase in heat treatment temperature from 600°C to 900°C resulted in rapid kinetics of phase transformation but affected the morphology of the coatings. An increase in coating thickness, number of coating layers, heat treatment time, and temperature resulted in an increase in overall total number of ordered phases and volume of ordered phases.

Bibliography: pages 96-104. / A hypoeutectoid steel has been heat treated to produce a range of different hardnesses and microstructures. A simulative field test rig has been employed to determine the relationship between microstructural parameters, material properties and soil constitution. Attempts have been made to correlate the ranking order for the wear resistance of similar treated steels in field and laboratory tests. It has been established that wear resistance is a function of soil constitution, steel carbide morphology and hardness. Explanations have been advanced for the differences in the wear resistance of similar steels in different soils based on the mechanism of material removal. Recommendations have been made regarding the selection of steel microstructure for varying soil conditions.

This work focuses on optimizing the sintering process of Ti-6Al-4V using Al-V master alloy powder to achieve a cost efficient product with acceptable mechanical properties. Reference was also made to Ti-6Al-4V products produced by Clinning (University of Cape Town 2012) using elemental Al and V instead of the master alloy addition proposed in this work. Commercially pure titanium (CP-Ti, Alfa Aesar) was used in this study as a reference, since its behavior during processing is more predictable. Relative density and the microstructural feature were studied in-depth in order to understand their impact on mechanical properties. The two starting materials were sintered under vacuum (approximately 10-5 mbar) at 1000⁰C (6hrs), 1100⁰C (2, 4, 6hrs), 1200⁰C (1, 2, 4hrs) and 1300⁰C (1, 2hrs). Relative density, microstructure analysis and mechanical property measurements characterized on the as-sintered material before specimens were hot deformed at 800⁰C to 0.69 strain and subsequently annealed at 870⁰C for 1hr. Similar measurements and analyses were conducted on the samples post deformation and annealing.

The relationship between microstructure and electrical resistivity has been studied in palladium-tungsten and palladium-molybdenum alloys, which exhibit an anomalous increase in resistivity after annealing. The effect of dislocations and structural order on resistivity has been investigated in order to determine the mechanisms whereby changes in resistivity occur in these alloys. The electrical resistivity of palladium-tungsten and palladium-molybdenum alloys has been determined as a function of annealing temperature, using a sensitive electronic apparatus purpose-designed for the present work. For alloys of low solute concentration a minimum in the electrical resistivity with respect to annealing temperature, which has not previously been reported, was observed. Specimens subjected to annealing experiments have been studied by means of transmission electron microscopy, in order to determine the effect of annealing on microstructure and structural order. The information obtained bas been used to relate the measured changes in electrical resistance and microhardness to the structural evolution of the alloys. It is concluded that the unusual resistance effects observed arise from competition between changing degrees of structural order and dislocation density. Which of these mechanisms predominates under given conditions varies as a function of solute concentration and annealing temperature. In alloys containing more than 6 at.% solute, recovery and recrystallisation processes are accompanied by an increase in resistivity and a decrease in microhardness; after recrystallisation is complete, further annealing bas no significant effect on either property. In alloys containing less than 6 at.% solute, recovery and recrystallisation are accompanied by a decrease in both resistivity and microhardness; but further annealing results in an increase in resistivity. Consideration of this data leads to the conclusion that microbardness is more sensitive to changes in dislocation density than structural order, whereas electrical resistivity is more sensitive to structural order than dislocation density. On this basis it is shown that short-range order increases rapidly at low annealing temperatures in alloys containing more than 6 at.% solute, but slowly in alloys containing less than 6 at.% solute in which short-range order increases rapidly only at higher annealing temperatures.

Bibliography: pages 133-136. / A survey has been made of the quality and type of materials used for tillage tools in South Africa. Conclusions have been drawn regarding the inadequacy of the manufacturing processes used and the resultant quality of the tool material. A rig has been designed for the abrasion testing of materials in soil. The reproducibility of the method has been shown to be high and an evaluation has been made of the relative wear resistance of a series of ·heat treated steels. A medium carbon boron steel has been shown to have great promise as a tillage tool material because of its high wear resistance and toughness. The deformed surface layers and the mechanisms of wear of steels subjected to field and laboratory abrasive testing has been examined. The removal of material through predominantly ploughing or cutting mechanisms has been shown to be dependent on the heat treatment and composition of the steels together with the nature of the abrasive. White surface layers have been observed to form on medium and high carbon steels subjected to soil abrasion. Suggestions have been advanced for their formation. Attempts have been made to assess the transferability of data between field and laboratory testing.

The erosion of ashlock hopper valves in coal gasification systems, and the maintainance downtime resulting from this erosion, is a cause of considerable concern to the coal conversion industry. After an assessment of the factors considered relevant to solid particle erosion as presented in literature, a design for a laboratory test apparatus to closely simulate the in-service problem was proposed. A test rig prototype, reproducing service conditions of temperature, pressure and geometry, was constructed and preliminary testing conducted. Various problems impairing the efficient operation of the test facility became apparent and these, together with the proposed solutions and modifications to the prototype rig, are discussed. Both room temperature and elevated temperature (400°C) erosion tests were conducted on the hardfacing seat material presently used on site as well as a on selection of common engineering materials. Optical and scanning electron microscopy (SEM) studies revealed a close correlation between in-situ and laboratory erosion damage, suggesting that the test apparatus is a valid simulation of the service problem.

An investigation has been carried out into the effect of rapid solidification on the microstructure and structural order present in dilute Au-Ti alloys, and the subsequent evolution of these properties on post-solidification heat treatment. Alloys of compositions lwt.% Ti, 2wt.% Ti, 3wt.% Ti and 5wt.% Ti have been rapidly solidified by a technique known as chill block melt spinning (CBMS). The microstructure and structural order present in the alloys both directly on solidification and after post- solidification heat treatment have been characterised using optical microscopy, scanning electron microscopy and transmission electron microscopy; the evolution of the mechanical properties on post-solidification heat treatment has been determined by means of microhardness tests. The flow characteristics of the molten alloys are observed to deteriorate with increasing Ti content resulting in an increase the cooling rate experienced by the alloys during rapid solidification with increasing solute concentration. The as-solidified alloy microstructures are therefore rationalised on the basis of variations in both cooling rate during CBMS and solute content. TEM examination of the as-solidified ribbons demonstrates that alloys containing up to 3wt.% Ti exhibit little evidence of either solute segregation or the formation of the equilibrium, long-range-ordered (Dla) Au₄Ti phase. In a 5wt.% Ti alloy the (Dla) Au4Ti phase is observed to nucleate during processmg. Long-exposure electron diffraction patterns from 2wt.% Ti, 3wt.% Ti and 5wt.% Ti alloys reveal diffuse intensity maxima consistent with the presence of <1½0> special-point order, a state of order which has not been identified previously in Au-Ti alloys. On the basis of electron diffraction patterns taken from these alloys the incorporation of elements of both DO₂₂ and Dla structures within the lattice is appropriate in the description of the structural order giving rise to special-point reflections. The state of order present in the as-solidified 2wt.% Ti and 3wt.% Ti alloys is shown to be best described by incorporating both elements of <1½0> special-point order and elements of the (D1a) long-range-ordered structure. In addition, the nature and distribution of the three-dimensional diffuse streaking observed in zone-axis patterns from a variety of different orientations is discussed and interpreted. This state of order is observed to be stable up to a temperature of 335°C. The lwt.% Ti alloy contained only 0.65wt.% Ti after processing. This loss of Ti results in extensive grain growth on heat treatment at temperatures above 350°C with no detectable second phase formation; as a result the alloy microhardness decreases on heat treatment. In the 2wt.% Ti and 3wt.% Ti alloys no grain growth is observed to occur on heat treatment at temperatures of up to S00°C. On heat treatment at 350°C the Au₄Ti phase is shown to precipitate in these alloys with a commensurate increase in the alloy microhardness. However, extended heat treatment at 500°C results in the coarsening of the Au₄Ti precipitates and is associated, in some instances, with a loss of precipitate coherency and an annealing out of orientational variants of the Au₄Ti phase.