Titanium alloys with good combinations of toughness and strength are being designed for aerospace applications: e.g. aeroengine compressors and aircraft undercarriages. It is not an easy process to optimise the balance between toughness and strength in this system, and in practice some aspects of the physical metallurgy of titanium alloys are not very well understood, such as the B2-type ordering in titanium alloys. The aim of this work mainly concerns the development of thermodynamic models, based upon CALPHAD techniques (CALculation of PHAse Diagrams). First-principles calculations were performed in order to provide the thermodynamic modelling with information concerning sublattice occupation. The energies of formation of different point defects in the ordered B2 phase of the Ti-Al binary system have been predicted. The dominant point defects in the sublattice of the B2-TiAl structure were determined to be either substitutional vacancies or anti-site defects, depending on the major element in the alloy. The concentrations of total and thermal point defects were estimated in the present work. The results of first-principles calculations have been adopted in the CALPHAD thermodynamic modelling. Thermodynamic assessment of the Ti-Al-Cr-V quaternary system was carried out, neglecting substitutional vacancies. A two sublattice model for B2 phase (Al,Cr,Ti,V)0.5:(Al,Cr,Ti,V)0.5 was used and a set of self-consistent thermodynamic parameters is presented. The predicted phase equilibria and order/disorder transformation temperature are shown to be in good agreement with experimental information, both in the Ti-Al-Cr-V quaternary system and in the important binary and ternary subsystems. The modelling results were used to predict the B2-stable region, which is important for the design of titanium alloys. Next, substitutional vacancies were taken into account in a thermodynamic model of the B2 phase (Al,Ti,V,Va)0.5:(Al,Ti,V,Va)0.5 in the Ti-Al-V ternary system, taking into account the theoretical results of first-principles calculations. The temperature of the β transus in Ti-6Al-4V alloy has been predicted to aid simulation of microstructure evolution. Experiments were carried out in order to calibrate the thermodynamic models, and to investigate the effect of B2-ordering on the kinetics of α precipitation from the β matrix. By using the obtained thermodynamic parameters, two databases of atomic mobilities were developed – one with substitutional vacancies and the other without. The calculated results from both databases fit the experimental data: concentration profiles, diffusivities and diffusion paths. Finally, microstructural kinetics associated with the β/α phase transformation in the Ti-6Al-4V alloy has been simulated using the phase-field method coupled with the CALPHAD approach. The needle-shape α structure was simulated and the mechanism of formation of Widmanstätten α structure was studied.

In this study, ZnO, MgO, In2O3, SnO2, iron oxide nanowires and nanorods were successfully produced by using Pulsed Laser Deposition. It was observed that the parameters, such as gold nanodots, number of pulses on the targets, temperature, oxygen pressure and substrate, contribute to various results. Different metal catalyst or substrate results in different morphology. Controlling oxygen pressure and substrate temperature was found to be crucial for the ZnO, In2O3 and iron oxide nanowires growth using this technique. The morphology of ZnO nanowires is highly influenced by plasma plume. Increasing the shots on gold target would increase the width of MgO nanorods, but by increasing the number of gold pulses, the distribution of the sizes and dimensions of ZnO nanorods become smaller. However, in the case of In2O3, retaining the total number of gold shots between 5 shots and 25 shots is critical. The variation of the number of laser pulses on oxide target mainly affects the length of nanowires in the case of MgO. However, in regards to In2O3, it does affect both the width and length of the nanowires.

Rare earth metals are at highest supply risk of all metals for clean technologies due to supply restrictions. Rare earth elements are essential for the highest energy permanent magnets which are used in high-tech green applications such as wind turbines and electric motors. This rare earth 'crisis' has been addressed by many authors by reducing or substituting the rare earths for less critical elements. The focus of this thesis, however, is on recycling of rare earth magnetic materials. Previous work has been focused on recycling NdFeB by re-sintering and blending alloying elements to improve the final magnetic properties. However, none of these studies have addressed the systematic addition of alloying elements or the particle size effect on the final magnetic performance of the recycled magnet. The work in this thesis is aimed at maximising the magnetic performance of recycled NdFeB magnets by investigating the effect of the manufacturing route and the influence of adding alloying elements. Uncoated end-of-life sintered NdFeB were exposed to hydrogen at room temperature to break them down into a friable powder; which was then milled, sieved, aligned, pressed and sintered into recycled magnets. The resulting magnets were tested on a permeameter at room temperature, 75 and 150oc to measure the magnetic properties. Scanning electron microscopy was used to assess the microstructures. Mechanical properties such as Vickers hardness and fracture toughness were also studied.

A parametric investigation of the crack susceptibility of laser deposited nickel superalloy CM24 7LC was conducted, using Design of Experiments (DOE) methodology to correlate the laser deposition processing variables (laser power, scanning speed, deposit dilution, laser spot size) against the cracking response. Also investigated was the effect of tool path pattern, powder particle size and substrate preheating. Results showed that cracking occurs during solidification, due to the presence of a low melting point eutectic composition liquid that forms due to elemental segregation of alloying elements, which resides at grain boundaries and other solidification boundaries, at temperatures below the solidus creating a weakened area that separates under an applied tensile stress. Cracking was reduced, but not eliminated, by using a high heat input approach comprising of high laser power, slow scanning speed, large laser spot diameter and low dilution. Different toolpath patterns produced various microstructures, with the cross hatch toolpath producing the lowest cracking response due to the generation of competing stress fields that reduce the net tensile stress available to form cracks. Powder particle size range was also observed to influence the crack density, with finer powders increasing the number of cracks, but decreasing the average crack length.

The microsegregation of alloying elements (Mn, Si and Ni) in as-continuously cast steel slabs were characterised by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The segregation profiles were obtained by cumulative profiles method using weighted interval rank sort (WJRS) and single element sort (SES) schemes. Analytical approaches (Ciyne-Kurz and Scheil), Thermo-Calc (thermodynamic) and DICTRA (considering the cross-effect of different elements) were used to predict the segregation behaviour of each steel slab. The segregation profiles predicted by DICTRA agree with experimental results better than those predicted by other models for each steel. But for slab I, root mean square deviation (RMSD) value used to determine the difference between DICTRA predicted and experimental segregation profiles was less than the experimental standard deviation. Directional solidification (OS) trials were carried out to verify DICTRA simulations in term of cooling rate. Although, DICTRA prediction using the measured cooling rate fell into the scatter band of WIRS profiles, discrepancy between the simulation and best fit to the profiles was found in the centre of both the dendritic and interdendritic regions. The discrepancy may indicate that the diffusions of Mn, Ni and Si in δ-ferrite used in DICTRA are faster than real situations.

A metal/peptide interface was developed to nucleate hydroxyapatite from aqueous solution. To achieve this, three different modifications were performed on mirror polished Ti-6Al-4V (MPT): 1) thermal oxidation (TO) at 500, 600, 700, 800 °C, 2) chemical treatment with H2O2/HCl and 3) chemical treatment with H2O2/HCl followed by TO at 500, 600, 700, 800 °C. It was found that with the increase of the TO temperature the topography increased and the composition of the surfaces changed, forming TiO2 crystals and increasing the Al2O3 content on the surface. These changes affected locally the surfaces charge behaviour in acidic and alkaline aqueous environments that were clue to the electrostatic interaction between the peptide, which presented positive and negative charged amino acids, and the surface. The peptide adsorption was highest on the surfaces that was chemically treated and thermal oxidised at 500 °C. The peptide coating was confirmed on the surface by the change of the charge behaviour in acidic and alkaline aqueous environments and its chemical composition. In addition, the growth of hydroxyapatite (HA) was obtained on the peptide coated surfaces confirming its bioactivity. Finally, it was shown that the surfaces with HA presented a better cell adhesion than the other modified surfaces.

A greater understanding of the PEPT process in dense materials has been achieved. PEPT is dependent upon the γ-ray attenuation between a tracer particle and the detectors of a positron camera. A lower limit for the radioactivity requirement for the positron camera used, was determined. PEPT in metal casting, was verified by recovering a particle from the location it had been tracked to during an experiment. An increase in the maximum temperature used with the process was also achieved. The effectiveness of ceramic foam filters was studied, the proportion of particles which passed through filters with pore sizes ranging from 10 to 30ppi was shown. The passage of inclusions through an open topped launder was also physically studied; A new geometry for a PEPT positron camera was specifically developed. In addition to the physical experiments a computer model was written, giving some additional insight into the behaviour of particles travelling through the launder. The model shows particles within the steady state flow of an industrial launder, into which a baffle was placed in the path of both the metal and the particles. Direct comparisons between the simulation and the physical experiment were drawn.

The micromechanisms of fracture in an austenitic/ferritic super-duplex stainless steel (Zeron 100) have been studied for a range of product forms, including cross-rolled plate, conventional (ingot) route and powder route extruded pipe, hot isostatically pressed (HIP'd) powder, and weldments produced using both tungsten inert gas (TIG) and manual metal arc (MMA) techniques. The rolled plate material was also investigated after heat treatments at temperatures of 425 and 850°C, which were known to embrittle the material.

Austenitic stainless steels are commonly used as heat exchanger tubing in power plants. As a result, this class of steels have been optimised to withstand high temperatures and pressures. However, under these conditions, the alloy will experience oxidation which greatly affects the lifetime of the materials. The increased likelihood of more cyclic operating conditions means a greater level of understanding of the oxidation and spallation behaviour of these alloys is required. High temperature oxidation studies available in the literature principally emphasise isothermal oxidation of flat plates rather than curved surfaces representative of boiler tubing. The isothermal and cyclic steam oxidation and spallation behaviour of TP347H FG was studied in this thesis. Electron microscopy and elemental characterisation showed the oxide encompasses an inner Fe-Cr-Ni spinel and an outer magnetite layer. A haematite layer forms during initial stages of oxidation in air-saturated steam conditions similar to the oxides formed in plant. The use of a novel technique, termed STORME, made it possible to identify the chemistry of the spalled oxide and also allowed calculations of the interfacial fracture energy to be made and the spallation mechanism to be identified. Modelling of the spallation observed enables predictions of spallation behaviour to be made.

The manufacture of an air-melted, Durville cast, nickel-iron based superalloy, XD1102, for the automotive industry has been studied. In particular the formation of the air-gap and the heat transfer between the casting and the mould interface has been measured for an aluminum alloy, LM25 and the XD1102 alloy cast into the same size mould. The experimental results were used to verify ProCAST 3D model simulations providing confidence that the software could be used for practical applications where destructive measuring techniques is not viable. A second aspect of this thesis was to identify, trace the origin of, illustrate the root cause analysis, and the mitigation of a feature which has been observed on numerous valve heads. Lastly the investigation into whether the substantial thermo-mechanical work received by an ingot after casting minimised the benefits of a carefully poured cast via the Durville method has been discussed.