Stress corrosion cracking is one of the leading damage mechanisms in low-pressure turbines in the power generation industry; in LP turbine blades it primarily occurs in the last stage blades. The research investigated the influence of tempering temperature on the microstructure, mechanical properties, and stress corrosion cracking properties of 12% chromium FV566 stainless steel, which is used to manufacture LP turbine blades. The standard heat treatment of the steel comprises of austenitising, quenching and double tempering. Austenitising is carried out at 1050°C for one hour - which is sufficiently long to generate a fully austenitic matrix and to dissolve carbon completely. Subsequently, the material is quenched in air. The high level of alloying elements ensures the complete martensitic transformation, with carbon atoms trapped in the matrix and distributed homogeneously. Thereafter, tempering of the material at 580-600°C enhances the ductility and toughness. Tempering replaces the solid solution strengthening of the dissolved carbon with precipitation strengthening by carbides. The final microstructure of the FV566 steel blades is referred to as tempered martensite. van Rooyen showed that for 12% chromium steel tempering at and above 600°C induces passivity of the material against SCC, while tempering of 12% chromium steels at 450-550°C causes sensitisation of the material and the material exhibits intergranular SCC. From such studies, the motivation arises to investigate the impact of heat-treatment parameters - specifically the impact of tempering temperature on the stress corrosion behaviour of the material. The testing methodology comprises heat treatment of FV566 samples at 1050°C for 1 hour, at 350°C for 1 hour, and thereafter tempering for 1 hour at various tempering temperatures. Each stage of heat treatment is followed by air cooling - followed by analysis of the microstructure, mechanical testing and stress corrosion cracking testing of the specimens at the different temper conditions. Stress corrosion testing was divided into two categories. The first set of tests was carried out with U-bend specimens to determine the susceptibility of materials at different heat treatments to SCC, the time taken for SCC to initiate, and the mode of cracking. The second set of tests was conducted to determine the threshold stress intensity, as a function of crack growth rate, for each heat treatment. The SCC failure mechanism observed was intergranular SCC (IGSCC) by anodic dissolution for the 550°C, 560°C, 570°C, 580°C, 590°C, 600°C and 620°C specimens. The material's resistance to SCC improved with increasing tempering temperature. Specimens tempered at 480°C and 550°C were most susceptible to SCC, while specimens tempered at 600°C The material's resistance to SCC improved with increasing tempering temperature. Specimens tempered at 480°C and 550°C were most susceptible to SCC, while specimens tempered at 600°C were immune to SCC in a 4000-hour period. A change in tempering temperature results in a change in the quantity and type of precipitates formed which results in changes in SCC properties of FV566.

Life assessment of critical components and piping is performed in the electrical power plants in order to prevent structural/component failure and prolong safe operation of the equipment. In the event that these components fail, the consequences can be very costly since this may result in power supply disruptions, component replacements, environmental damages and the loss of human life. Regulations, standards and codes are designed to ensure the safe operation of the power plants. However, on their own, they are not adequate to account for aging power plants that have been in service for more than half of their originally designed lifespans, since failures have been experienced due to in-service aging mechanisms (i.e. temper embrittlement, creep, etc.) and poor engineering and maintenance practises. Mechanical, metallurgical and non-destructive techniques are used to evaluate the condition of the in-service materials in order to aid in these life assessments. The structural integrity assessments utilise material toughness properties as determined through fracture toughness testing, which requires a significant quantity of material, and is therefore cumbersome and expensive. Consequently, several other material property testing techniques are used to aid in structural integrity assessments, such as impact energy, tensile and hardness testing. Through empirical correlations, these test results are used to estimate fracture toughness properties and, consequently, the error bands are expected to be as high as 50%. Due to its small size, the small punch test (SPT) technique can be regarded as a quasi-non-destructive test, and is therefore a preferred method for determining the fracture toughness in aid of structural assessment. The SPT technique involves a compression load from the punch to a sample (ϕ8mm x 0.5mm thick) clamped between clamping and receiving dies. This study aims to develop a test rig that will be used to perform the SPT in order to quantify the level of embrittlement on the ex-service, low-pressure steam turbine material (NiCrMoV steel). The data results acquired from the SPT technique are the reaction load of the punch and the deformed displacement of the sample performed at a constant displacement rate according to CWA 15627:2007. Two SPT rigs were designed, manufactured and commissioned. These two were commissioned using FEM and tensile test results for validations. The steel was subjected to three different conditions: as received (AR), de-embrittled (DE) and hardened (HD). The three types of steel illustrated that the SPT can quantify embrittlement levels through the correlation of tensile, Charpy impact energy and fracture toughness testing.

Includes bibliographical references (leaves 121-125). / The Pt₈V ordering transformation in Pt 11 qt.% V alloys has been studied. The study included determining the thermodynamic stability of Pt₈V, the kinetics of Pt₈V ordering transformation and the strengthening due to the presence of the ordered phase. Transmission electron microscopy, using election diffraction and dark and bright field imaging, and X-ray diffraction were used for structural characterisation. Electrical resistivty was used to investigate the kinetics of Pt₈V ordered phase. Microhardness measurements were used to investigate the Pt₈V ordered phase and its effects on hardness.

Includes bibliographical references. / A study has been conducted on both the particle and slurry erosive wear behaviour of WC-Co hard metal coatings. The coating compositions were WC-12%Co and WC-10%Co-4%Cr and were produced using both the TAFA JP5000 and the METCO Diamond Jet (DJ) thermal spray systems.

Includes bibliographical references (leaves 210-219) / An investigation into high strain rate behaviour of polymer composites was performed by developing a finite element model for a fibre reinforced polymer (FRP) plates impacted at varying strain rates. The work was divided into three facets, firstly to characterize the FRP material at varying strain rates, to develop a constitutive model to elucidate the relationship between strain rate and ultimate stress and lastly to use the experimental data to develop a finite element model. Experimental work performed in support of this model includes material characterization of unidirectional carbon and glass fibre reinforced epoxy at varying impact strain rates. The data is then used to develop a suite of constitutive equations that relate the strain rate, ultimate stress and material loading type. The model is of a linear and non-linear viscoelastic type, depending on the type of loading and is applicable to a FRP plate undergoing out-of-plane stresses. This model incorporates techniques for approximating the quasi-static and dynamic response to general time-varying loads. The model also accounts for the effects of damage, the linear and non-linear viscoelastic constitutive laws reporting failure by instantaneously reducing the relevant elastic modulus to zero. An explicit solver is therefore utilised in order to ensure stability of the numerical procedure. Glass fibre reinforced plastics (GFRP) was found to be more strain rate sensitive in all directions when compared to carbon fibre reinforced plastics (CFRP). The validation process therefore involves plate impact experimental testing on GFRP plates. The data from these experiments compare to within 8% of the finite element model that incorporates both damage and the developed strain rate sensitivity constitutive equations. For the first time a model that includes progressive damage with built-in strain rate sensitivity is developed for these particular FRP systems. Furthermore, the ultimate stress has been related to strain rate using an empirical technique. This technique allows for the prediction of dynamic ultimate stresses given the quasi-static ultimate stresses, again for this particular material systems.

The ultimate goal of this project was to explore alternative and various synthetic routes for the design and fabrication of V@Pt core-shell and bimetallic nanoparticles.

Includes bibliographical references (leaves 110-111). / The focus of this study was the use of powder metallurgy to produce low cost titanium with comparative mechanical properties to wrought titanium. The objectives of this investigation was to produce sintered titanium compacts that represented metal made by the Direct Powder Rolling method. The critical strain (ɛC) required to induce recrystallization following deformation was determined by hot compressing wrought titanium samples. Finally sintered titanium samples were hot compressed at ɛC and the changes to the microstructure, porosity and mechanical properties was assessed.

Includes bibliographical references / Two magnesium/silicon aluminium alloys each reinforced with 20 vol. % SiC particulates have been worn against three different automobile friction linings (brake pads). Two of the friction linings are commonly used against cast iron brake rotors while the third has been formulated for use against aluminium MMC brake rotors. Wear processes at the interfaces of the specific rotor - pad combinations have been characterised through the analysis of friction traces and the use of optical and electron microscopy. Models on the interdependence of friction and wear, and models of wear mechanisms for aluminium MMCs and cast iron sliding against friction materials have been proposed and discussed. For an aluminium MMC sliding against an organic pad formulated for use against cast iron, wear rates are low and friction is constant due to the formation of a solid lubricant layer at the wear interface. When this MMC is worn against a semi-metallic pad formulated for use against cast iron, wear rates are extremely high due to two and three body abrasion which lead to subsurface delamination and early melt wear in the MMC. For an aluminium MMC developed for its use in automobile brake rotors sliding against a semi-metallic pad specifically formulated for its use against MMC brake rotors, wear rates at low loads are low although friction traces are irregular and fracture of the SiC particulates occurs at the lowest load and sliding velocity. This fracture of SiC is caused by the abrasive action of hard alumina particles within the pad. At high loads and sliding velocities cohesiveness of materials within the pad is poor and the wear rate of the MMC is extremely high. At the highest load/sliding velocity combination, the wear resistance of the MMC is inferior to that of its unreinforced matrix. If the structure and composition of friction linings are arranged correctly, the wear resistance and frictional performance of aluminium MMC brake rotors are superior to those of cast iron brake rotors. In addition, the lower density of aluminium MMCs provides for an economic advantage over cast iron with respect to efficient use of fuel, and fabrication expenses.

Hot Plane Strain Compression (PSC) testing is a thermomechanical testing method used to simulate the deformation condition of industrial rolling. Thermomechanical processing (TMP) factors such as the amount of strain, strain rate and temperature all influence the microstructural evolution. The geometry of the PSC test sample and anvil are important factors in order to achieve the plane strain condition and acceptable strain distribution within deformed sample. Geometrical factors such as the breadth ratio (BR) relates the the samples breadth (b) to anvils face width (w) and this ratio has a significant effect on the breadth spread of the sample. The height ratio (HR) relates w to the samples height (h) and this ratio has a significant effect on the strain distribution. Two different geometric PSC testing configurations were investigated for this study, the one configuration had less favourable geometric ratios with a BR of 3 and a HR of 1 and the other configuration had more favourable ratios, with the BR of 4.62 and the HR of 1.3. This investigation is to evaluate the feasibility of a newly installed TMP machinery, the Gleeble 3800, to simulate the hot finishing rolling conditions by the use of hot PSC tests for the production of the can body stock (CBS) aluminium alloy AA3104. Single hot PSC tests were carried out at temperatures of 300, 350 and 400 ⁰C at strain rates of 10, 30 and 100 sec-1 and multi-pass hot PSC tests were carried out to simulate the different rolling passes experienced on the hot finishing rolling mill of the production of the aluminium alloy AA3104. The strain rate, temperature control, flow stress and microstructural flow were investigate to establish whether PSC testing is feasible on the Gleeble 3800.

A study has been made of the slurry erosion resistance of a series of cemented tungsten carbides with different binder compositions consisting of combinations of cobalt, nickel and chromium. Testing was carried out on a specially designed laboratory rig in both tap and salt water using silica sand as an erodent. The synergistic action of erosion and corrosion on WC hard metals results in greatly enhanced wear rates compared to either erosion or corrosion processes alone. Cemented carbides with a 1 0 wt% binder were found to have a better slurry erosion resistance than the corresponding 6 wt% binder grades or the pure metal binder alloys alone. The performance of all the materials was found to be much worse in a salt water medium compared to tap water. The alloying of either pure Nickel or Cobalt binders was found to influence the fracture properties and corrosion resistance and lead to an improvement in the slurry erosion resistance of the cemented carbides. However any improvement in the corrosion resistance of the binder did not directly enhance the slurry erosion resistance of the cermet. Explanations are advanced to explain these differences in behaviour linked to chemical composition, mechanical properties of the binder phase and the dynamic nature of the slurry erosion system. Comparisons are also made between the performance of the Ni-Cr-Co based cermets and the pure alloyed metal binder grades. The acceptability of modelling the slurry erosion and corrosion resistance of cermets based on the behaviour of the binder phase materials is discussed.