Ni contributes about 60% of austenitic stainless steel manufacturing material price. This means that the price of austenitic stainless steel increases with an increase of Ni. Ni price fluctuation has led to major efforts to reduce its content in austenitic steels. Ni has been replaced with readily available, cheap elements such as Mn and N. Hercules™ is a low Ni austenitic stainless steel alloy that was developed at Mintek in the Advanced Materials Division as part of the new development of low Ni austenitic stainless steels. The typical content of Hercules™ comprises of 2 wt.% Ni, 9 wt.% Mn and 2.5 wt.% N When Hercules™ alloy was tested at Mintek for mechanical properties, it was found that it had higher tensile strength than Type 304 in the hot rolled and annealed condition. Therefore, it was concluded that it can be used for structural applications where high strength is required. The target applications for Hercules™ were reinforcement bars and fasteners. There has been work done in order to improve corrosion resistance of Hercules™ in order for it to be used in corrosive environments or for general purposes. A more corrosion resistant Hercules™ alloy with 0.5 wt.% Mo addition was developed. The current project focused on further characterisation of the corrosion resistance of Hercules™ B (with 0.5 wt.% Mo) and Hercules™ A (without Mo addition) against Type 304 and Type 202. Cyclic polarisation technique was used to test the susceptibility of Hercules™ to pitting, crevice and general corrosion in different solutions. Hercules™ B showed better resistance to pitting in 3.56 wt.% NaCl compared to Hercules™ A and Type 304 but, it showed poor resistance in the presence of an artificial crevice. When the concentration of NaCl was reduced to 1 wt.%, Hercules™ B showed better resistance to crevice corrosion compared to Type 304, while Type 202 consistently showed poor corrosion resistance during each test. Immersion tests in 6 wt.% FeCl3.6H2O were consistent with the results that were obtained from the cyclic polarisation technique. The critical pitting temperature (CPT) test was investigated using 6 wt. % FeCl3.6H2O immersion testing. All test alloys started pitting at 25℃, meaning that they all have a CPT value that is less than 25℃. The results obtained from ten-days immersion and cyclic polarisation test in 5 wt.% H2SO4 were also consistent with each other. All test alloys showed good performance in 5 wt.% H2SO4 by achieving a corrosion rate that is less than 0.1 mm/y. It was therefore, concluded that Hercules™ B has an overall corrosion resistance that is comparable to that of Type 304 in 5 wt.% H2SO4 and 1 wt.% NaCl.

Includes abstract. / Includes bibliographical references (leaves 132-144). / The development of new technologies and the demand for improved performance has resulted in the need for materials with high specific strength and stiffness. Fibre reinforced polymer materials have found increased application in the automotive and aerospace industries by virtue of their excellent specific properties, good corrosion resistance, toughness and fatigue properties. This study aimed at the feasibility of developing an advanced hybrid thermoplastic composite for aerospace and automotive applications. This was done by first researching the types and functions of current thermoplastic composites used in the aerospace and the automotive industries. Thereafter, an advanced thermoplastic resin was selected as matrix to develop the hybrid composites which were then characterised by mechanical and physical testing.

A range of aluminium alloys and particulate reinforced aluminium metal matrix composites has been tested in an apparatus which simulates the erosive-corrosive action of a slurry. The slurry consisted of silica sand suspended in either distilled water or synthetic mine water. Several steels were also tested in order to clarify certain concepts relating to the synergistic effects of erosion and corrosion. In general both the heat-treatable and non heat-treatable aluminium alloys exhibit lower slurry erosion rates with increasing hardness and work to fracture values. The slurry erosion rates of the aluminium matrix alloys increase with increasing amounts of reinforcement particles. For the steels a good work hardening capacity and/or high hardness values are found to promote good slurry erosion resistance. All the steels exhibit lower slurry erosion rates than the aluminium alloys. A corrosion cell was developed to allow in situ electrochemical measurements to be made. The addition of corrosive ions to the distilled water results in increased material removal rates, increasing by as much as 40% for some of the aluminium alloys and 41%for the 304 stainless steel. The aluminium alloys and the steels which have increased corrosion resistance due to passivity, display poor performance under the slurry erosion-corrosion conditions tested. Paradoxically corrosion resistance was found to have a detrimental effect on the slurry erosion-corrosion resistance of a material.

Bibliography: pages 147-152. / This thesis examines the fracture toughness behaviour of a series of cemented carbides having carbide grain sizes between 0.35f.Lm and 4f.Lm, cobalt contents ranging from 6 to 15wt%, and vanadium carbide contents from 0 to 0.8wt%. A series of twenty-four ultrafine WC-Co alloys were sintered from powders produced through three different production routes, namely, the spray conversion process and two variations of the conventional powder production methods. A further twelve WC-Co alloys with three different carbide grain size distributions were produced through conventional powder metallurgy processes. Two different fracture toughness test methods have been used to determine the toughness measurements, namely, the Palmqvist Indentation test and the Short Rod test. A Terra Tek Fractometer machine was used to automatically determine the Short Rod toughness values. The Palmqvist testing was carried out on a Vickers hardness machine using indenting loads of 20, 30 and 50kg. The Palmqvist crack lengths were measured by summing the individual crack lengths emanating from the corners of the hardness indentation. These crack lengths were used in a formula developed by Shetty et al., to calculate the Palmqvist fracture toughness. The influence of annealing at 800°C and 900°C on the Palmqvist crack lengths has also been assessed. Microstructural parameters have been determined using ASTM procedures and microscopy techniques and the influence of these parameters on the fracture toughness has also been assessed.

This work is an attempt to evaluate the influence of critical operational parameters on the high temperature erosion of a 1Cr½Mo boiler tube steel. Erosion testing has been carried out in a specially designed and developed unique laboratory apparatus capable of simulating the conditions of temperature, particle velocity and flux as found in the economiser region of pulverised fuel boiler combustors in electricity generation power plants. The work has encompassed the effects of particle type, size, velocity and flux on the erosive wear rates of the 1Cr½Mo boiler tube steel at temperatures of up to 600°C. The response of the target to impacting erodent particles has been analysed using scanning electron and optical microscopy, transmission electron microscopy (TEM) as well as conducting cross-sectional microhardness tests. The change in the mechanical properties of the steel was determined by conducting tensile tests over a range of temperatures from 20°C to 565°C.

Two alloys, Pd 11.1 at.% Cu and Pd 11.1 at.% Nb, predicted to form the A8B ordered structure, were investigated. Prior deformation with systematic heat treatments was used to promote ordering, hardness tests were used to detect changes in the microstructure, which might result from ordering. The Pd-Cu alloy and Pd-Nb alloy did not exhibit any significant hardness changes when heat treated. Transmission Electron Microscopy (TEM) was used to aid detection of any A8B ordered phase in the Pd-Cu alloy. It was concluded that no ordering had occurred and any initial hardness variation was anomalous. The Pd-Nb alloy was further characterised using Differential Scanning Calorimetry, but no transformation was observed. The Pd-Cu alloy was predicted by other workers (after commencement of this project) to have a very low ordering temperature, which probably accounts for the lack of ordering at the temperatures reported here. The Pd-Nb alloy is concluded to be extremely slow in atomic rearrangement, so that unfavourable thermodynamics prevented ordering of the alloy during this project.

A series of four ultrafine WC-Co alloys of varying cobalt contents has been sintered from powder produced through the spray conversion process. The materials have been characterised and subjected to slurry erosion and cavitation erosion. A further twelve WC-Co alloys of varying grain sizes and cobalt contents have been produced through conventional processes and subjected to the same tests in order to provide data for comparison. The erosion resistance of all the grades tested was found to increase with decreasing grain size, both under cavitation erosion and slurry erosion conditions. Furthermore, a transition from a localised material removal mechanism to a bulk material removal mechanism was observed in both erosive systems as the WC grain size of the material decreased below about lμm. The erosion resistance of sub-micron materials was found to be considerably more sensitive to bulk deformation parameters than that of coarser materials. As a result, ultrafine grades subjected to slurry erosion or cavitation erosion were found to exhibit lifetimes up to seven times greater than those of the best-performing materials with grain sizes above 1 μm. This increase in erosion resistance was achieved without any significant drop in fracture toupness. Significant differences were observed between the response of WC-Co to the two erosive systems, particularly in those materials exhibiting a localised erosion response. Under slurry erosion conditions, these materials displayed increasing erosion resistance with decreasing cobalt content, and both the cobalt and WC phases responded to erosive attack. Under cavitation erosion conditions, however, the opposite trend was observed, and only the cobalt phase responded to erosive attack. Materials exhibiting a bulk erosion response responded in a similar fashion to both forms of erosive attack, although cavitation erosion produced damage to a greater depth. The effect of defects on material performance was found to depend critically on the erosive system.

A study has been made concerning the tribological behaviour of ultrahigh molecular weight polyethylene (UHMWPE) during water-lubricated reciprocating sliding wear. The experimental work has been extended to study also the effect of molecular weight, fillers, lubrication, counterface roughness and sliding configuration on the polymer's transfer characteristics. The wear behaviour of polytetrafluoroethylene (PTFE) has been included for comparative studies. The worn material was studied using stylus profilometry, optical microscopy, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), Transmission electron microscopy (TEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), differential scanning calorimetry (DSC), infrared spectroscopy (IR) and mass spectrometry. The effect of two fillers, namely glass beads and a titanium-based inorganic filler on the friction and wear behaviour of UHMWPE has been investigated as a function of counterface roughness (Rₐ). It was found that the filled material exhibited lower wear rates than the unfilled material on the rougher counterface. The filled material was also found to be more sensitive to a change in Rₐ and showed higher wear rates than the unfilled polymer on the smooth counterface. A uniform and coherent transfer film is found on the rougher counterface but the transfer film for the titanium-based filler was patchy on the smooth counterface. No coherent transfer film was found when sliding was conducted parallel to the grinding direction on the steel counterface, resulting in relatively high wear rates. Polymer transfer was patchy, the amount increasing as the sliding distance increased. The observed phenomena are explained in terms of mechanical interlocking and chemical bonding of the polymeric material with the metal counterface. An increase in molecular weight did not significantly improve the wear resistance of the UHMWPE. Small variations in counterface roughness values (Rₐ) were found to have a much greater effect on the wear rates than changes in molecular weight. The steady-state wear rate of the polymer was furthermore found to be more dependent on an adherent transfer film rather than a change in bulk morphology. Although PTFE exhibited low friction coefficients, the high wear rates obtained by this polymer is explained by the polymer's inability to form a transfer film under water lubrication, while any film that forms under dry sliding wear is easily peeled off the surface. Significant improvements in wear are found when fillers are added to the polymer. The wear rates for PTFE under dry sliding are similar to those obtained for UHMWPE under water lubrication. Transfet of UHMWPE material to the metal counterface during sliding wear involves interlamellar shear of the polymer and results in the development of a highly oriented transfer film. Significant differences have been found in the degree of crystallinity, crystallite size and orientation in the deformed surface layers of the polymer and debris compared with those of the bulk polymer. The worn surface of the polymer shows slightly increased crystallinity but the crystallinity of the debris is much higher than that of the bulk whilst the crystallite size is much reduced.

The sliding wear behaviour of ultrahigh molecular weight polyethylene (UHMWPE) sliding against partially stabilised zirconia (PSZ) and alumina ceramic counterfaces in various lubricating media was investigated. Wear tests were conducted in order to investigate the effect that the addition of proteins to the lubricating solutions had on the wear behaviour of the UHMWPE against a smooth counterface of PSZ . The lubricants selected were physiological saline solution, distilled water and physiological saline solution containing small additions of synovial fluid and up to 15'% by volume of albumen solution. The effect of the addition of proteins to the lubricating solutions on the production of wear debris was also studied. ii The effect of changing the counterface roughness from Ra of 0.01 μm to 0.06μm was also investigated. The wear behaviour of UHMWPE against alumina ceramics in distilled water was compared to that of UHMWPE against PSZ in similar conditions.

Bibliography: leaves 170-179. / Polypropylene is an extremely versatile polymer because its properties can be modified to meet specific requirements. The use of polypropylene in domestic and automobile applications has initiated research focused on the tribological behaviour of the material. In the present study, polypropylene grades have been subjected to both mild and severe abrasive wear conditions with specific emphasis on the surface property of scratch resistance. The experimental work has covered the effect of polymer crystallinity, mineral fillers, and the nature of the abrasive counterface on the wear behaviour of polypropylene. The wear behaviours of polymethylmethacrylate, polycarbonate, acrylonitrile-butadiene-styrene, and high density polyethylene have been determined for comparative purposes. The abrasive wear rates have been measured and the material deformation and removal mechanisms have been identified and characterised in terms of the physical properties of the polymer and the individual fillers, and in terms of the macroscopic mechanical behaviour of the filled composite materials. Investigative techniques used in this study included mechanical testing, optical and scanning electron microscopy, surface profilometry, and differential scanning calorimetry. Under two-body abrasive wear conditions, the unfilled and modified polypropylene materials exhibit a ductile mode of material deformation and removal.