The nickel-base superalloy MarM-002 is a high strength precipitation hardening material used in structural applications in the gas turbine field. The microstructure of MarM-002 consists of fine y' precipitates, a y matrix, carbides and a eutectic y- y' where the y' can be composed of coarse lamellae or blocky y' precipitates. Increasing the volume fraction of fine y' by dissolving the coarse eutectic y' during solution treatment can raise the alloy strength. In practice the solution heat treatment temperature does not usually exceed 1220°C because of the danger of incipient melting. At 1220°c the eutectic y' does not dissolve and persists in the alloy structure. In the current project an alternative solution treatment technique, the varied rate solution heat treatment (VRSHT), was determined specifically for MarM-002, and was used to achieve higher solution treatment temperatures up to 1260°C without incipient melting. The microstructural response of MarM-002 to the conventional 1220°C solution heat treatment, and to solution treatment at temperatures above 1220°C, was studied extensively. Microstructural features such as carbide decomposition and the degree of y' and eutectic y' dissolution were noted. The tantalum and titanium rich carbides which form during casting were seen to decompose during solution treatment, while hafnium rich carbides precipitated in the interdendritic regions during heat treatment. The y' solvus and eutectic y' solvus was measured to be1260°C and 1280°C respectively. A 1050°C/12h +_ 870°C/16h ageing heat treatment was applied to the alloy following solution treatment and the effect on the y' characteristics was also studied.

Ti-6Al-4V is a two phase alloy used in the aerospace, military and biomedical industries. The thermomechanical processing (TMP) of Ti-6A-4V involves the breakdown of the ingot microstructure at temperatures above the beta transus (Tβ) into fine lamellar colonies. Subsequent hot deformation is carried out at temperatures within the two phase region to produce a microstructure that is either equiaxed or bimodal. However, to avoid the formation of shear bands, voids or cracks within the final microstructure, this secondary fabrication is carried out at slow speeds, and these render the TMP of titanium a time consuming and expensive process. This project aims to investigate the possibility of using a steckel mill for the TMP of Ti6Al4V. A steckel mill is a single stand reversing mill with 2 coiler furnaces on either side. These furnaces allow for the annealing of strip metal in between passes thus keeping the strip at a high temperature throughout processing. In this way, reversing passes can occur indefinitely until a desired gauge thickness is achieved. A steckel mill therefore represents a cheaper and faster method to produce metal sheet or plate. Ti-6Al-4V cylinders with a diameter of 10mm and length of 15mm were uniaxially compressed in the Gleeble 3800. Hot compression was carried out isothermally in a 3 pass schedule at temperatures of 850°C, 950°C and 1050°C. The strain was kept constant at 0.48 and strain rates of 1/s and 10/s employed. Interpass times corresponding to a strain rate of 10/s were 44s and 77s, whilst those corresponding to a strain rate of 1/s were 324s and 712s. Statistical analysis in the form of analysis of variance (ANOVA) was used to determine the parameter most influential on the microstructural evolution of Ti-6Al-4V and the Taguchi method used to identify the optimum parameters suitable for the TMP of Ti-6Al-4V using a steckel mill. Three successive passes at 850°C, 1/s resulted in a microstructure consisting of coarse, deformed grains and some finer recrystallised grains. The influence of a low strain rate was such that it promoted recrystallisation at this temperature, while that of interpass time brought about recrystallisation and grain growth. At the same temperature and a strain rate of 10/s, less recrystallisation, together with a heavily deformed microstructure was observed. This was due to the heterogeneous distribution of strain which was a consequence of the high strain rate used. At 950°C, at both 1/s and 10/s, 1 pass resulted in a bimodal microstructure. With subsequent passes, the amount of equiaxed alpha was observed to increase. This increase was a result of a strain induced phase transformation (SIT) from beta to alpha at high temperatures. The extent of this transformation increased with an increase in strain rate. Therefore, after 3 consecutive passes at 10/s, a fully alpha (though heavily deformed) microstructure was formed. A subsequent post deformation heat treatment would lead to recrystallisation of these grains and a microstructure consisting of refined equiaxed grains the result. After 1 pass at 1050°C, at either 1/s or 10/s, a Widmanstätten microstructure was formed. However, after 3 consecutive passes at 1/s, the microstructure remained mostly Widmanstätten whilst at 10/s, a bimodal microstructure was formed. The combination of a high strain rate, low interpass times, sequential strain imparted on the sample as well as the high temperature at which the compressions were carried out, elevated the extent to which a strain induced phase transformation from alpha to beta proceeded. Statistical analysis using ANOVA and the Taguchi method revealed that a schedule of 3 passes performed at 1050°C, 1/s and the corresponding interpass times as being the optimum parameters for the TMP of Ti-6Al-4V during steckel mill rolling. Analysis of the microstructural evolution across all 3 temperatures, however, showed that 3 passes carried at 950°C, 10/s, with interpass times of 44s and 77s, as being the optimum parameters. Steckel mill rolling of Ti-6Al-4V has thus been confirmed as a feasible process for the production of Ti-6Al-4V sheet material.

Includes bibliographical references. / This dissertation describes an investigation into the application of fracture mechanics to brittle materials, with particular emphasis on the fracture toughness testing techniques used on these materials.

Includes bibliographical references. / This work is an investigation into the phenomenon of three-body abrasive wear. A specially designed three body abrasive wear apparatus has been built, modified and evaluated as part of this overall study. Further, a series of commercially available candidate materials has been evaluated for wear resistance using silica sand as the abrasive on this purpose made rig. The effect of normal load, abrasive particle size, abrasive feed rate and the type of abrasive on three body wear resistance has also been examined. It has been shown that there is little increase in wear with an increase in particle size in the size range from 50µm to 180µm and that above an abrasive particle size of approximately 200µm there is a sharp decrease in the wear with increasing particle size, followed by a levelling off in the wear. The wear was found to increase linearly with increasing load. Varying the abrasive feed rate showed that at lower feed rates the abrasive particles were more efficient at removing materials, so the wear was higher than at higher abrasive feed rates. It has also been shown that although the use of ash from coal-fired power stations as an abrasive produces wear of materials, the volume losses were much smaller than those obtained using silica sand and thus it is considered that the tests using silica gave results which were more reliable. The volume losses of alumina ceramics abraded against ash were insufficient to give reliable wear test data and it was concluded' that ash could not be used to rank materials of high hardness. A number of materials were ranked for wear resistance using silica sand abrasive particles. The alumina ceramics and tungsten carbide composite materials showed the best wear performance.

Contains published articles. / Bibliography: p. 131-138. / Experiments on the behaviour of brittle materials, particularly quartz, during the initial period of loading, at the onset of fracture and during the stage of rapid crack propagation, have been performed in order to gain an insight into some of the fundamental processes of brittle fracture which might prove useful in the solution of practical problems in mining and process operations. Studies have also been conducted into the nature of the damage produced by a diamond stylus sliding on a quartz surface. The results of these studies have been correlated with ancilliary experiments in which the effects of the deformation produced by a sharp indenter and sliding diamond polishing particles on quartz were examined. The geometry of cracks in glass and quartz during the loading stage has been observed by scanning electron microscopy and was found to be approximately elliptical. By making some simple assumptions, an equation has been derived that enables the fracture surface energy to be deduced from shape of the crack and the loading conditions. The brittleness of a material is indicated by the difference between the fracture surface energy and the thermodynamic surface energy of the material. In a perfectly brittle body they are equal. In order to make an accurate comparison with the true surface energy in quartz as calculated from atomic bond energy data, anisotropic elastic theory was used in the evaluation of the fracture surface energy.

An investigation was performed on alloys of a 12wt% Cr steel (3CR12) that had undergone different thermomechanical processing routes prior to the annealing step of production. The aim of this research was to identify any changes in the annealing response of 3CR12 steel due to the different thermomechanical processing routes to which the alloys had been subjected. Three alloys of 3CR12 were subjected to various cooling treatments immediately following hot rolling. This was accomplished by water quenching, air cooling and insulatory cooling of the hot-rolled plates. Characterisation of the alloys in the hot-rolled and annealed conditions included optical and electron microscopy, macro- and microhardness tests, tensile tests and impact energy tests, dilatometry, differential thermal analysis and volume fraction analysis. Alloys in the as-rolled state exhibited an increase in martensite content related to an increase in the cooling rate following hot rolling. The increase in martensite content influenced the alloys' mechanical properties by raising their bulk hardness, UTS and yield strength. This was coupled with a decrease in the elongation and impact toughness of the alloys. Furthermore, the Ac1 was found to increase with higher cooling rates following hot rotting. Variations in the as-rolled microstructures influenced the alloys' subsequent annealing response, with there being a greater and more immediate response to the annealing treatment by alloys subjected to higher cooling rates after hot rolling. The fully annealed alloys showed little variation in their microstructures or mechanical properties, despite clear variations in their as-rolled microstructures.

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.