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.

In this work, a series of Mn-based borohydrides were synthesized by mechanochemical milling of ABH\(_4\)-MnCl\(_2\) (where A=Li, Na, K) under argon. Samples prepared by milling xLiBH\(_4\)-MnCl\(_2\) (where x = 2 or 3) resulted in the formation of Mn(BH\(_4\))\(_2\) and LiCl in a stoichiometric ratio. Thermal decomposition of Mn(BH\(_4\))\(_2\) was observed between 105 and 180°C with the concurrent evolution of hydrogen and diborane. Analysis of the decomposition products suggested the presence of amorphous B, Mn and LiCl. When NaBH\(_4\) was used as a reagent, Mn(BH\(_4\))\(_2\) was also observed, however instead of NaCl, a solid solution of NaCl\(_x\)(BH\(_4\))\(_1\)\(_-\)\(_x\) and Na\(_6\)MnCl\(_8\) were formed. Mn(BH\(_4\))\(_2\) decomposed between 110 and 170°C for xNaBH\(_4\)-MnCl\(_2\) with the concurrent evolution of hydrogen and diborane. Analysis of the decomposed samples showed that amorphous B and Mn formed (110 to 170°C) and NaCl\(_x\)(BH\(_4\))\(_1\)\(_-\)\(_x\) reacted with Na\(6\)MnCl\(_8\) to produce NaCl (250 to 475°C). When KBH\(_4\) was used as a reagent, Mn(BH\(_4\))\(_2\) was not observed. Rather, K\(_2\)Mn(BH\(_4\))\(_4\), KMnCl\(_3\) and unreacted KBH\(_4\) were observed. The mass losses for the milled sample were observed between 100 to 160°C with a release of hydrogen and trace diborane, forming KBH\(_4\), B, and Mn, and between 165 to 260°C with only hydrogen release, giving KCl, B and Mn.

The measurement of materials properties and the control of processing parameters is important for both materials development and quality control. Determination of these parameters is sometimes advantageous if done by means of microstructural characterisation as here additional information may be gained from the sample. These values, e.g. the grain size or the volume fraction of the present microconstituents, may allow the correlation with mechanical properties or processing properties. Unfortunately, the diffusional and displacive transformation products, martensite and bainite, exhibit very fine microstructures with a low contrast, so that conventional microstructural image analysis cannot be applied readily to distinguish these structures. As an alternative microstructural characterisation technique texture analysis based on Haralick parameters calculated from second order grey value statistics was successfully applied. It has been shown that the analysis of large sample areas can be done automatically enabling the correlation of the texture data with the respective local microhardness using a neural network. The analysis is limited due to the dependence of the texture parameters on preparation and imaging conditions. A more detailed understanding of the individual Haralick parameters will be the basis to extend the method to a correlation with other properties of the sample that may be not easily accessible by physical testing, such as toughness.

MgO thin films were deposited on Si (100) single crystals, NiW tapes, 310 austenitic stainless steel and Hastelloy C276 by the ultrasonic Spray Pyrolysis technique, using magnesium nitrate and magnesium acetate as precursors at many different conditions. Thermogravimetrical analysis (TGA) of the decomposition of the precursors was used as a guideline temperature for the thin film deposition. Biaxially textured and epitaxial MgO films were deposited on Si substrates using magnesium nitrate precursors. An amorphous MgO thin film was deposited on NiW tapes, NiO buffered NiW, 310-stainless steel and Hastelloy C276 when using low concentration of the magnesium nitrate precursor. Higher concentrations were needed to obtain (200) oriented MgO films on C276. However, NiW tapes and 310-stainless steel were found to be a non suitable substrate for MgO thin film deposition due to surface instability. A (200) oriented MgO thin film was grown on Hastelloy C276 using a magnesium acetate precursor at a much lower concentration compared to the nitrate precursor. The ISD deposition by spray pyrolysis (irrespective of the used precursor and the used substrate) produced MgO films that grew with the (200) normal to substrate surface as distinct to MgO films grown by thermal evaporation which grew with the (200) tilted to the substrate normal. Pulsed laser deposition (PLD) was used to deposit YBCO on MgO buffered substrates. The characterization of the thin films was done using SEM, EBSD, XPS, AFM, X-ray diffraction 2-scans, rocking curve (-scans), phi () scans, X-ray pole-figure measurements, and AC susceptibility. YBCO deposition by PLD on Si substrates buffered with MgO was not successful due to the thermal stresses developed in the MgO buffer. An EDX line scan performed on MgO films deposited on Hastelloy C276 from the acetate precursors confirmed the effectiveness of such layer as a diffusion barrier. It was found that c-axis oriented YBCO films were grown on c axis oriented MgO films deposited on C276 from the nitrate and acetate precursors; however, MgO and YBCO films have a very weak in-plane texture. The AC susceptibility measurements show that the YBCO films have a broad superconducting transition temperature irrespective of the precursor used. To improve the superconducting transition temperatures, different annealing treatments were performed on the MgO buffer deposited on Hastelloy C276, however, it was found that the as deposited MgO buffer films and subsequent deposition of YBCO films gave the best superconducting transition temperatures. In an attempt to improve the in-plane texture of YBCO, CeO2 was deposited by PLD on the spray pyrolysed MgO.