The hardening behaviour of three cold-worked platinum alloys, Pt 5 at% Mo, Pt 5 wt% Ru and Pt 5 wt% Cu, has been investigated through a systematic series of heat treatments. All three of the experimental alloys showed a hardness increase during annealing within a specific temperature range. The hardness of the Pt-Mo and Pt-Ru alloys was found to increase rapidly at annealing temperatures above the recrystallisation temperature, with the final hardness similar to the original coldworked hardness. The hardness of Pt-Cu showed an increase of up to 30% at low annealing temperatures of between 200°C and 500°C. In addition, the Pt-Cu alloy also showed the increased hardness found in Pt-Mo and Pt-Ru at high annealing temperatures, but the hardness increase was not to the same extent. Specimens subjected to the annealing treatments were studied by means of optical, scanning electron and transmission electron microscopy, in order to determine the effect of annealing on microstructure and structural order. Resistivity, XRD and OTA techniques were employed in order to study the mechanisms of ordering with temperature, but these techniques did not produce any significant results. It was concluded that the most likely cause for the hardness increase observed in all three experimental alloys was due to a change in structural order upon annealing. The Pt-Mo and Pt-Ru alloys hardened through an increase in short-range order at annealing temperatures above the recrystallisation temperature. The Pt-Cu alloy hardened through the development of long-range order on annealing between 200°C and 500°C. This increase in hardness was in· addition to the high dislocation density in the alloy specimen due to prior cold-work.

A laboratory carburising furnace in which metal dusting conditions are simulated has been designed and constructed. This furnace has been used to simulate and study the metal dusting corrosion of four iron-based alloys viz. 9Cr Mo 45 steel, Incoloy 800H, AISI 310 stainless steel and Chromanite - an experimental high-nitrogen Cr-Mn stainless steel (HNSS). Tests conducted on the carburising furnace show that the rig is capable of heating a flowing gas environment to temperatures of 800°C in the horizontal ceramic tube. The design allows the testing of up to thirty-six test specimens in a constanttemperature test zone. Systems for the safe heating and disposal of gases such as hydrogen and carbon monoxide have been incorporated into the design. Four twenty-four hour exposures were performed on specimens of the CrMo steel and as received samples of AISI 310. This was followed by a series of seven week-long exposures of Incoloy 800H, AISI 310 and the high nitrogen stainless steel (HNSS). These specimens were tested in an annealed and polished condition in order to increase their susceptibility to metal dusting. In a third test series, specimens of these three alloys were tested in an annealed and abraded condition in order to determine the effect of grain size and surface roughness on metal dusting resistance. Exposures of the CrMo specimens resulted in general metal loss and massive carbon deposition after the first exposure of 24 hours. Filamentous carbon deposits containing metal particles showed that metal dusting corrosion of the specimens had taken place. The as received AISI 310 specimens showed no signs of metal dusting attack over the same exposure time. This was attributed to a protective surface chromia layer that prevented carburisation of the specimens. During the second test series, specimens of Incoloy 800H in the sensitised condition showed a high susceptibility to metal dusting. Carburisation of the matrix carburisation was accompanied by large carbon protrusions growing from the specimens' surfaces. Large pits were observed on the specimens after five weeks. Sensitised AISI 310 specimens also showed signs of metal dusting but at a slower rate. The difference in performance between these two alloys was attributed to the difference in alloying contents, notably chromium, nickel and silicon. The HNSS specimens showed a high resistance to carburisation, carbon deposition and metal loss during the first six weeks. Small amounts of carbon deposition and pitting were observed after the seventh exposure. The good resistance to metal dusting of this alloy was attributed to its alloying contents, which included chromium, manganese, sulphur and nitrogen. The results of the third test senes showed that resistance to metal dusting was significantly improved by increasing the surface roughness and decreasing the grain size of the specimens. A new alloy, Fe-25Cr-12Ni-9Mn-4.5Al-2Si-0.5N is proposed for fabrication and exposure to metal dusting environments to evaluate its suitability for use in industrial applications. It is also recommended that further work be carried out in evaluating the effect of increasing the nitrogen, chromium and manganese contents of the Fe-18Cr- 9Mn-0.5N alloy that performed well in this project. Investigations into the effect of aluminising and nitriding components should also be carried out.

Includes bibliographical references. / This work addresses the problem of erosion of steel heat exchanger coils in a petroleum producing plant by magnetite catalyst particles entrained in the flowing gas stream.

Includes abstract. / Includes bibliographical references. / This research investigates the feasibility of producing Ti-6Al-4V products by creating low cost BE sintered preforms and then subjecting these preforms to thermomechanical processing (TMP) in an attempt to both improve the relative density and refine the microstructure. The powders used were direct reduction titanium powder and elemental aluminium and vanadium powders.

Bibliography: leaves 106-113. / The abrasive wear resistance of ruthenium aluminide intermetallic and ferritic steel containing an iron-chrome sigma intermetallic phase have been investigated in this study. A medium carbon wear resistant steel (MCV) was used in the study to facilitate comparison between wear resistances in the materials of interest. Specimens of ruthenium aluminide, MCV and ferritic stainless steels containing a sigma phase were produced. The MCV steel was quenched and tempered to match the bulk hardness of the as-received ruthenium aluminide. Five different grades of thermomechanically worked ferritic steels specimens were heat treated to produce different volume fractions of sigma phase. The mechanical properties of the specimens were investigated by compression testing and microhardness measurements. Abrasion testing was carried out on a pin on belt abrasion apparatus. The surface response of the specimens to abrasive wear was characterised by optical and scanning electron microscopy. Microhardness of the specimens were measured with a digital microhardness machine. The wear resistance of ruthenium aluminide was found to be higher than all materials tested in this project. The wear resistance in some of the ferritic steels containing sigma phase was comparable to that of the wear resistant medium carbon steel. The surfaces of the specimens were shown to work-harden during the abrasion process. The corresponding work-hardening results showed that ruthenium aluminide had the highest work-hardening rate. It can be concluded that the work-hardening ability of the test materials correlates with their respective wear resistance properties.

Includes bibliographical references (leaves 124-127). / Hydrogen was used as a temporary alloying element in CP Ti and Ti-6AI-4V. The microstructural evolution and phase transformations were monitored, before, during and after hydrogenation with in-situ dilatometric testing. Wrought CP Ti and Ti-6AI-4V specimens were pre-annealed and experienced four consecutive thermal cycles (Cycles 1-4) i.e. hydrogenation, post-hydrogenation, dehydrogenation and post-dehydrogenation, during dilatometric testing. The specimen in each thermal cycle was heated to 1000°C, heating rate 1°C/min (with an isothermal hold at 1000°C for three hours for hydrogenation and dehydrogenation cycles) and then cooled to room temperature at cooling rate of 1°C/min.

Includes bibliographical references. / The work covered in this thesis provides a comprehensive discussion of the transformation behaviour of Type 304 metastable stainless steels with small' variations in alloy composition. The study focuses mainly on the austenite stability with respect to alloy composition, rate of deformation and temperature. To achieve these objectives, uniaxial tensile tests at 0.3 true strain were performed at low and high strain rates (10-3s-1 and 3 x 10-2s-1 respectively), in the temperature range of -60 to 55°C under isothermal testing conditions.

Includes bibliographical references. / The erosion behaviour of titanium aluminide intermetallic alloys has not been widely reported in the scientific literature and is part of the current international research effort aimed at exploiting these materials for turbine engine and automotive applications. In the present study titanium aluminides have been subjected to both solid particle erosion and cavitation erosion. The erosion rates have been measured and the damage mechanisms have been identified and discussed in terms of the microstructures and mechanical properties of the titanium aluminide alloys. This has been achieved with a variety of investigative techniques, including electron microscopy, mechanical testing and microstructural examination; and, where necessary, the erosion performance of other materials have been evaluated for comparison. In particle erosion, conducted with air blast rigs at room temperature and at elevated temperature, the titanium aluminide alloys exhibit a ductile mode of material removal, and their limited strain to fracture results in higher particle erosion rates than those for 304 stainless steel. Heat treatment to produce changes in microstructure and hardness does not significantly affect particle erosion performance, and elevated temperature tests reveal an increase in particle erosion rate with increasing temperature. In cavitation erosion, the titanium aluminide alloys exhibit a ductile mode of damage accumulation and material loss, and the rates of material loss are lower than those for other engineering materials such as 304 stainless steel and some hardmetal grades which are currently used in erosive environments. The mechanism of cavitation erosion of the Ti₃Al-based alloy involves the accumulation of strain in phase boundary regions and the preferential removal of the more brittle component of the microstructure. For the Ti₃Al-based alloy, cavitation erosion resistance increases with an increase in hardness produced by heat treatment. The TiAl-based alloys exhibit twinning during the initial stages of cavitation, which is characteristic of the high strain rate deformation of TiAl-based alloys, followed by substantial work hardening and preferential material loss from phase interfaces and twinned regions.

Includes bibliographical references. / A study has been made of the tribological behaviour of ultra high molecular weight polyethylene (UHMWPE) and ion implanted UHMWPE during water lubricated reciprocating sliding against differing stainless steel and Yttria Partially Stabilised Zirconia (YPSZ) counterfaces. A new laboratory test apparatus was designed, built and commissioned to facilitate this research. The new apparatus is capable of simulating the reciprocating wear of a sliding couple under diverse conditions of pressure, sliding speed and lubricant environment, as well as allowing the measurement of frictional forces 'encountered between the two surfaces in sliding contact. Variation in stainless steel counterface surface roughness resulted in three different types of wear behaviour.

Bibliography: p. 100-106. / This thesis examines the influence of austenite potential and hot roll finish temperature on the evolution of microstructure in the ferritic stainless steel grade AISI 430. In particular, it focuses on the influence of these variables on the hot band annealing behaviour of this steel. The material employed was obtained from laboratory and commercial heats. Two hot roll finish temperatures, viz. 600°C and 800°C for the commercial heats and two alloy compositions of austenite potential 11 and 61% for the laboratory heats were studied. Electron channelling contrast (ECC) obtained in scanning electron microscopy was used to follow the evolution of microstructure. Limited micro texture measurements were made using electron backscattered techniques. It was found that a low finish temperature produced a hot rolled microstructure that showed limited softening and a fully recrystallised microstructure after annealing while a high hot roll finish temperature produced a completely softened as-hot-rolled microstructure and only partial recrystallisation after annealing. A high austenite potential encouraged the ferrite phase to undergo extensive continuous recrystallisation during hot band annealing. However, the affinity for the precipitation of carbo-nitrides tended to play a role in slowing down the process. On the other hand, the ferrite phase deformed in the presence of a low austenite content mostly underwent extended recovery during hot band annealing. The softening here was affected by a low driving force. The end microstructures after annealing were however similar in both cases in as much as they consisted of elongated structures. The martensite phase was found to behave similarly regardless of the austenite content, where both recovery to produce subgrains and occasional recrystallisation occurred. During final recrystallisation after cold rolling, the high austenite potential coupled with a short hot band anneal time resulted in incomplete recrystallisation. This caused sharper alpha fibre texture components in the final sheet. A long hot band anneal time however resulted in sharper gamma-fibre texture components. In the case of low austenite potential, a long hot band anneal produced a random texture in the final texture. Ridging was observed in all cases but a high austenite content was found to lessen its severity. Also, it (ridging) was reduced by the random texture produced by long hot band annealing in the case where the austenite potential was low.