Bibliography: pages 76-82. / An investigation involving the erosion of WC-Co alloys by solid particle impact erosion was undertaken to determine the mechanism by which material is removed. For this purpose a simple particle-gas stream erosion apparatus was employed. The nineteen different WC-Co alloys studied were initially characterised according to mi crostructural and mechanical properties. An investigation of the influence of various parameters on erosion was conducted to establish the manner by which the WC-Co alloys were eroded. A limit in erosion rate occurred with increasing particle size for all samples, which is associated with ductile erosion. The variation of erosion rate with the angle of impact was found to be dependent on the binder content. A maximum in erosion occurred at a 90u angle of incidence for the low cobalt content alloys and in the region of a SOU angle of incidence for high cobalt content alloys. Thus suggesting a predominantly brittle mode of erosion, with a ductile mode becoming more important with increasing binder content. The erosion rate was found to increase with decreasing hardness. For impact angles of 45u and greater, the hardness effect was masked by microstructural influences. Examination of the steady state eroded surface and the single particle impact event, using the scanning electron microscope revealed three modes of material removal. These may occur simultaneously, the predominant mode, however, changes with binder content. For WC-Co alloys containing less than 10 wt-% cobalt, cobalt extrusion was observed as being the controlling mode of material removal. Maximum carbide grain cracking was associated with a cobalt content of 10 wt-%. Above this binder level ductile cutting of the matrix became an increasingly important mode of material removal.

Bibliography: pages 79-86. / This thesis involved a study of the phase transfonnations in a chromium containing corrosion resistant dual phase steel, designated 3CR12. The objectives included the detennination of time-temperature-transformation (TTT) diagrams for the transformations between austenite and ferrite and an investigation into the factors controlling these reactions. The austenite decomposition reaction for a high nickel alloy, 3CR12Ni, and the effect of varying titanium concentrations on the equilibrium phases present in 3CR12, were also examined. Dilatometry was used to determine the transformation temperatures between austenite and ferrite and the Ms temperatures for the alloys investigated. The kinetics of the reactions were investigated by optical microscopy using two different etching techniques while the volume fractions of the various constituents were determined by a point counting method. Transmission electron microscopy was used to study the carbide morphologies and the nucleation and growth modes of the phases during the transformations. The distribution of the alloy elements were determined by microhardness measurements, an electronprobe microanalysis and a Kevex spectrometer attached to a scanning electron microscope. The 3CR12 alloy used in this study did not become fully austenitic above the Ae₃; it lies in the nose of the gamma loop of the Fe-Cr phase diagram. Two temperature regimes were identified on the decomposition of austenite. At 750°c the existing ferrite grains grew into the austenite matrix, while at 650° C and 700°C new ferrite was sympathetically nucleated i.e. it was heterogeneously nucleated on existing ferrite/austenite grain boundaries. Two types of carbide morphologies were formed. These were random precipitation within the ferrite grains and interphase precipitation. The TTI diagram showed conventional "C" curve kinetics. The austenitisation reaction occurred by a para-equilibrium mechanism. The rate controlling process was the structural change from ferrite to austenite; the reaction was not long range diffusion controlled. The speed of the reaction increased continuously with increasjng transformation temperature. No growth of ferrite occurred on isothermal transformation of 3CR12Ni at temperatures below the Ae₁. Increasing the bulk titanium content increased the Ms, Ae₁ and Ae₃ temperatures of 3CR12 due to the removal of carbon from, and the addition of titanium to, solution.

Many of Eskom's coal fired power plants have an average age of 170 000 hours and a few operating close to 300 000 hours. Main steam temperatures experienced in a power plant vary between 535-555°C. These operating conditions place main steam pipe components to operate within the creep regime. It is of utmost importance for safety and plant health that these critical components are managed to determine the remaining life and risks associated with high temperature exposure for prolonged periods of time. Non-destructive testing (NDT) methods are utilised extensively on Eskom power plants to determine the remaining life and replacement strategies for critical components. Surface replication is used as a life assessment tool for creep damage quantification of main steam pipe work. A large part of maintaining plant is repair welding on creep aged and sometimes creep aged material as entire system replacements are impractical and time consuming. By repair welding new material onto creep aged material, mechanical and microstructural properties of the creep aged material deteriorates. The study of this work is focused on characterising the as-received materials from Eskom power plants and using these creep aged materials to create cross-weld samples with virgin material. The cross-weld samples were creep-rupture tested at high temperature and low stress conditions to determine the fracture location of repair welded cross-weld samples. Once ruptured, the zone of rupture, was identified and created in a larger volume by simulation using Gleeble® thermo-mechanical equipment. The as-received base materials were subjected to different operating conditions hence contain different degrees of creep damage. The microstructural evaluation of the creep damaged material was conducted using optical microscopy, scanning electron microscopy (SEM), coupled with more advanced electron backscattered diffraction (EBSD). Microhardness and hot tensile testing were included to characterise the mechanical degradation of the as-received material. The fracture location of the creep-ruptured cross-weld samples were investigated using optical microscopy, SEM and EBSD and occurred on the outer region of the heat affected zone (HAZ) of the creep aged material. The fine grained microstructure with coarse precipitation of this region is characteristic of the fine grain heat affected zone (FGHAZ). The occurrences of voids predominantly occur in this narrow region with very few voids in the adjacent base/weld material. As this zone is of particular interest due to it being the weakest region in repair welded joints, the need to investigate it further is important. A larger testing volume of the FGHAZ was created by applying a weld thermal cycle simulation to the as-received base materials. The impact of this simulation was determined microstructurally by optical microscopy and mechanically by hardness and tensile testing. The FGHAZ has low creep resistance and is most susceptible to failure due to the small grained microstructure. Due to the numerous small grains, there is a high effective diffusion coefficient (HEDC). The multi axial stresses induced during in service/ creep testing conditions together with the HEDC causes voids to form at an accelerated rate. Significant void coalescence promotes the formation of micro cracks which in turn lead to macro crack formation and eventually failure.

Includes bibliographical references. / Includes bibliographical references (leaves 96-103). / The high usage of Al and its alloys in both the automotive and aerospace industries is attributed to its excellent specific strength and corrosion resistance. High demand of Al usage has led to the improvement of both the casting techniques and joining processes, in order to improve on the quality of the final product. The selection of the manufacturing process for Al and its alloys is based on the capabilities of the specified requirements for components and the alloy used. High pressure die casting (HPDC) is the most widely used casting process in the automotive industry due to its high production rate, and ability to produce complex shaped components. However, HPDC is prone to porosity making it difficult to heat treat and weld. Semi solid metal (SSM) forming has the potential to produce near-net-shape components with high integrity. Due to laminar filling characteristics of SSM HPDC, low porosity or porosity free castings can be produced. This offers the opportunity to apply heat treatment as well as weld the SSM HPDC components. A high continuous wave Nd: YAG laser has been used to investigate the weldability of SSM cast A356 alloy. The CSIR rheo-process was used to prepare the aluminium A356 SSM slurries and thereafter plates (4X80X100 mm3) were cast using a 50 Ton Edgewick HPDC machine. Plates in the as cast, T4 and T6 heat treatment conditions which had passed radiography inspection were then laser welded. Some of the initial as-cast plates that were welded were subjected to pre or post weld T4 or T6 heat treatment and are referred to as pre-weld T4 or pre-weld T6 and post-weld T4 or post-weld T6 specimens.

Includes bibliographical references (leaves 145-149). / Corrugated board is a composite sandwich type material used in the packaging industry worldwide. In the design of corrugated boxes, the stacking strength is an important design parameter. Current research shows that box failure is influenced by the flexural rigidities of the panel and its transverse shear rigidities. McKinlay proposed a new method to measure the MD transverse shear stiffness of corrugated board. This research was aimed at designing a fixture to perform the MD shear test and to evaluate its performance. In addition, the properties that influence box strength were to be investigated. These properties were then to be used in improved box strength predictions. It was found that the designed MD shear fixture was able to measure the transverse shear stiffness of corrugated board in the MD direction with a high degree of accuracy and reproducibility. This method was much easier to perform than the standard block shear test method and also much quicker. This was a very important factor considering the application of this testing method in a research and development environment. In addition, the stiffness test exhibited good possibilities for use as a quality control tool. Extensive testing showed that the material used in the manufacture of corrugated board had a strong influence on board and box strength. In addition, it was found that the separation of the faces in a corrugated board structure had an influence on the strength and stability of the box. Factors such as the manufacturing process and board structure were also found to have an effect on box strength. Box strength predictions were performed using the methods available in the literature. These predictions had good correlation with the experimental box compression values. It was shown that box strength can be accurately predicted from liner and fluting properties and this capability is an important tool in box strength design.

Includes bibliographical references. / A study has been made of the fatigue crack initiation and fatigue crack growth behaviour of three different steels in wire form, namely, an austenitic AISI 304 stainless steel, a corrosion resistant ferritic steel, 3CR12, and pearlitic high carbon steel. The stainless steel wires were produced in the laboratory at a drawing speed of 50 mm min-1, without intermediate annealing, whilst the high carbon pearlitic steel was manufactured commercially. Studies were made on stainless steel wires as a function of drawing strain between 0.09 and 0.585. Fatigue testing was carried out on an ESH servo hydraulic testing machine on both notched and unnotched samples and the S-N curves were used to evaluate the fatigue properties of the steels. Tests were performed with sinusoidal loading and load ratios of R= 0.048 and R=0.22 at a frequency of 2Hz. The microstructural evolution during drawing was characterised by optical and transmission optical microscopy, and x-ray diffraction. Fatigue crack growth and fracture surfaces were studied using scanning electron microscopy. In general, the fatigue limit was enhanced by increased drawing strain, but such strain also increased the subsequent crack propagation rates. The highest value of fatigue limit of 630 MPa was exhibited by the commercial pearlitic steel despite of its high notch sensitivity. Both shot peening of the steel wire surface and reducing the surface roughness by manual polishing increased the fatigue limit between 40 and 25 % respectively. The fatigue limit of AISI 304 stainless steel wire was improved from 215 MPa to 650 MPa after drawing to 0.585 strain. This improvement is attributed to the deformation-induced phase transformation of (ϒ) austenite to α'-martensite. X-ray diffractometer traces show that the amount of strain-induced martensite varied from 8% in the wires drawn at low strain (0.09) to 36% in the wire samples drawn to 0.585 strain. This study has established that approximately 20% of deformation-induced martensite, through drawing strain, is a critical amount which determines the subsequent fatigue response of this steel. If the amount of previously developed martensite is less than the critical amount of 20%, the martensite formed during the fatigue process will act beneficially by retarding fatigue cracking, raising the fatigue limit and resulting in a ductile fatigue fracture surface. However, in the presence of more than 20% of martensite, any martensite induced by cyclic strain will encourage more rapid crack initiation compared to a material containing less than 20% martensite which leads to more brittle fracture surface characteristics. The fatigue limit of 3CR12 steel wire was also improved from 130 MPa to 310 MPa (maximum stress) after drawing to 0.68 strain. The experimental results indicate that the use of drawn 3CR12 ferritic steel for wire application under cyclic conditions is restricted to low stress levels. However, the application of heat treatment and the resultant development of a dual-phase microstructure, improved the fatigue limit to 470 MPa. Based on the findings in this study, recommendations regarding material selection and drawing process optimisation for wire production to improve the fatigue performance of AISI 304 stainless steel is given.

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.