High strength strip steels with a yield strength of ~700 MPa are used in the yellow goods industry, with recent trends requiring thicker strips with an improved toughness. Strip steel was produced to thicknesses of 10 – 17 mm, with thinner strips showing improved Charpy impact toughness compared to the thicker strip. It was found that all samples (different thicknesses and test orientations) showed splits on the fracture surfaces in the upper transition region. The hot rolled strip steels showed a predominantly fine-grained (~4 µm ECD) ferrite microstructure, with some coarse grain patches (grains ≥5 µm grouped together). No significant differences were noted for the grain size, yield stress, tensile strength, hardness and texture for the different compositions. Splits were characterised and produced successfully by low blow Charpy testing with acoustic emission (AE) sensors indicating the presence of splits which occurred in the upper transition region predominantly without main crack propagation. Analysis by x-ray tomography and sectioning was carried out showing splits propagate by transgranular cleavage, preferentially following coarse-grained regions, with the 10 mm strip producing deeper splits which was related to elongated grains (high aspect ratio). Therefore the presence of deep splits improved toughness through a reduction of the impact transition temperature, which was achieved by ensuring the presence of a bimodal grain structure, containing coarse elongated grain patches.

Poly(hydroxybutyrate) copolymers are sustainable and biodegradable, but they are known to exhibit secondary crystallisation, which severely reduces the ductility of these materials, thus hindering their current commercial use. Therefore, the main focus of this research was to explore a number of strategies to control the secondary crystallisation behaviour of two Poly(hydroxybutyrate) based copolymers. Blends of P(HB-co-HV)(3 wt % HV) with carbohydrate molecules of varying chain lengths were prepared by melt blending, characterised, and monitored over time to assess their capability to reduce secondary crystallisation. Additives were found to hinder the secondary crystallisation process, demonstrated by a reduction in the percentage change of mechanical properties as the concentration and chain length increased. The effect of storage temperature on the secondary crystallisation behaviour of P(HB-co-HHx)(33 % HHx) was also reported. Samples were stored at a range of storage temperatures and the effects on thermal, chemical and mechanical properties discussed. Increasing storage temperature caused the secondary process to occur to a greater extent, with greater increases in the melting temperature recorded in samples stored at 100 \(^∘\)C (128 \(^∘\)C - 135 \(^∘\)C) compared to samples stored at 7 \(^∘\)C (128 \(^∘\)C – 128 \(^∘\)C). Sub-melting point degradation of the material was also noted.

In this work, the deformation behaviour of Ti-6Al-4V micro-pillars was studied via compression tests at room temperature. Micro-pillars containing either the single α phase region or both α and β phases were prepared and either prismatic < a > slips or < c+a > slips were activated. Thin foils for TEM study were prepared using the FIB from the selected deformed pillars. STEM was used to image dislocations and their interaction with the α/β interfaces. Sample yield strength has been observed in all groups of micro-pillars and its relationship with the β phase, α/β interface, orientation and extrinsic sample size was discussed. The β phase is proved weaker than the α phase and the α/β interfaces behaviour as both the barriers and sources of dislocations. The magnitude of influence depending on the volume fraction, orientation and morphology of the β phase and the α/β interfaces. The work-hardening rate is related to the orientation of micro-pillars and the α/β interfaces in the micro-pillars. The strain bursts can be suppressed by the α/β interface and smaller sample size. The sample with smaller size expressed the larger strain burst in the stress-strain curves. The orientation influences the number and magnitude of strain bursts.

This thesis looks at the effect of micro segregation of Nb, generated from the continuous casting on grain structure development during reheating and deformation. The amount of segregated material present in the microstructure has been quantified in the as-cast condition and that has been used to model grain size distribution after reheating and deformation which is required for subsequent toughness prediction in 0.045 wt % Nb steel. The limits of validity of the original Dutta-Sellars model for predicting the amount of recrystallisation; investigating the influence of the variables such as starting grain size distribution, strain and Nb content has been examined. A modified Dutta-Sellars model considering the starting grain size distribution has been found to be more accurate in quantifying the amount of recrystallisation. This approach has been used to model grain size distribution after deformation both in the homogenised and in presence of Nb segregation. The effect of AlN, to replace Nb(C,N), on pinning the austenite grain boundaries during reheating has been investigated, as the segregation tendency of Al is much less compared with Nb.

The defect structure of single crystal tantalum with orientation 001, 011 and 111 after a 6 GPa shock loading with lateral and back release waves were characterised using scanning electron microscopy (SEM) and transmission electron microscopy. The SEM images were filtered using ImageJ script to determine the type and fraction of deformation twins. A methodology of imaging dislocations in the tantalum single crystals using electron channelling contrast was made with the assistance of the dislocation contrast profile simulation based on the dynamical theory of electron diffraction. The dislocation density distribution was measured using electron channelling contrast imaging (ECCI) technique. The nucleation and growth of the deformation twins are discussed with the aid of finite element simulation of the wave propagation in the material. The defect evolution and response of the single crystals are found to be highly dependent on the loading orientation of the shock wave. The effects of the lateral release wave and back release waves on the deformation mechanisms are also discussed.

In-situ TEM compression testing is able to probe quantitatively the mechanical response of materials with simultaneous imaging of the deformation microstructure evolution. Ti-6Al-4V (Ti64), known for high strength, is the most widely used Ti alloy. A better understanding of the plastic deformation micro-mechanisms is sought using in-situ TEM studies. This project investigates the dislocation characterization of bulk Ti64 and the dislocation activities in micro-pillars during in-situ TEM compression.

The purpose of this work was to determine the microstructure and secondary phase distribution in the TiB2 particulate reinforced Al-4.5Cu A205 alloy. This was extended to sand, investment and die casting techniques with the overall aim of optimising the existing solution heat treatment protocol for a variety of possible starting conditions. Additional work was aimed at determining a relationship between TiB2 additions and the observed globular microstructure. Hardness testing, DSC analysis, EDS and tensile testing were used to determine the effectiveness of heat treatment. It was found that a 4hr solution treatment at 538oC did not produce significantly different results from a 44hr, four step treatment process. As the diffusion behaviour of Cu was judged to be the most important factor affecting solution heat treatment, a simple microstructural model of typical A205 grain structures was proposed. The model was found to operate on similar timescales to those observed from experimental testing of A205 but was limited by idealised phase structures. The castability of A205 was determined using fluidity and hot tearing experiments. The better than expected castability was attributed to enhanced feeding brought about by the globular structure of A205.

A requirement for online monitoring has emerged owing to the susceptibility of fibre reinforced composite materials to sub-surface damage. Acoustic emission (AE) monitoring is understood to detect damage well before catastrophic failure; research in AE sensing therefore continues to attract significant attention. The research presented herein provides a review of a fibre-optic-based AE sensor design. Developmental work was performed to evaluate both sensor fabrication and packaging-related issues. The characteristics of the sensor were found to be influenced by: (i) the type of optical fibre used for fabrication; and (ii) preparation of optical fibres prior to sensor fabrication. The use of a small-diameter packaging substrate revealed improvements in sensor performance. The fibre-optic AE sensor was successfully embedded in a uni-directional composite laminate that was fabricated using autoclave processing. The embedded fibre-optic sensor was found to provide higher sensitivity to simulated AE compared with a surface-mounted sensor. Sensor characterisation trials were performed using simulated AE; a low directional sensitivity was observed. Modal analysis revealed a preferential sensitivity to the A0 wavemode; this sensor design may therefore be suited to the detection of delamination in FRCs. Finally, the sensor was shown to successfully detect interlaminar crack propagation under Mode-I loading.

This thesis describes hydrodynamic studies of the leach and solvent extraction stages of a Platinum Group Metal (PGM) hydrometallurgical flowsheet. The studies were motivated by the need to increase PGM throughput in Johnson Matthey’s PGM refining business. In the leach stage, key components in the feed are selectively dissolved using acids in a stirred tank before they are recovered by liquid-liquid (L-L) solvent extraction and finally purified. The work described in this thesis tackles four main areas: hydrodynamic studies of L-L PGM solvent extraction in both mixer and settler stages, whilst for the leach stage, studies of particle behaviour in gas evolving solid-liquid (S-L) reactions and gas-liquid-solid (GLS) characterisation by a novel Electrical Resistance Tomography (ERT) technique are performed. In the mixer-settler, the effects of impeller diameter, D, to vessel diameter, T, ratio (D/T), the phase flow ratio, cφ/dφ; (where cφis the continuous phase flow fraction and dφ is the dispersed phase flow fraction) and the specific power input,Tε, upon the droplet size distribution in a L-L system and their phase separation were investigated. Changing a smaller D/T impeller for a larger D/T impeller at constant P/V and cφ/dφincreased droplet size because the maximum shear rate decreased as a result of increasing ratio of impeller pumping capacity (Q) with tip speed (Utip). Changing a larger cφ/dφfor smaller cφ/dφat a fixed P/V and D/T impeller increased droplet size because turbulent dampening increased since the average density, ρ ∝ dφ. Meanwhile, Kolmogoroff-Hinze’s theory was shown to apply for the measured relationship between Tε and droplet size. A settler design criterion, which relates the dispersed phase concentration (Ca) in the dispersion band to the dispersed phase throughput (Qd/A) agreed with the model by Ryon et al. (1959). Ca was significantly dependent on P/V and Qd/A, whilst the effects of Qc/Qd (where Qc is the continuous phase flowrate and Qd is the dispersed phase flowrate) and D/T were minimal. Droplet size analysis of the sedimenting region of the dispersion band and dense packed layer revealed a transitional distribution of droplet sizes due to the counteracting effects of droplet sedimentation, hindered settling and droplet-droplet coalescence. Particle behaviour in gas evolving S-L systems were quantified using the Zwietering ‘just-suspended’ impeller speed (Njs) condition in a sponge nickel® and sodium hypochlorite system. The presence of gas caused Njs to increase, however a coherent relationship between Njs in an ungassed and gassed system 3 could not be easily ascertained. Further work with Positron Emission Particle Tracking (PEPT) was advised to quantify the relationship. A well-known electrical concept called skin effect, which describes how the effective resistance of an electrical conductor varies as the frequency of an alternating current (AC) increases and decreases, was used to investigate GLS behaviour via a novel ERT spectroscopic technique. The process relies on the change in effective resistance of conducting objects with changing AC frequency to selectively detect different phases. The concept was initially validated with static phantoms of a stainless steel and plume of gas before being applied to dispersible stainless steel particles and gas. ERT spectroscopy showed that two AC frequencies (0.3 kHz and 9.6 kHz) could successfully isolate and simultaneously detect the gas and solid phases at a fixed current. By subtracting solids and gas conductivity, the change in solids and gas holdup were obtained.

Due to high hydrogen capacity, good reversibility and low cost, magnesium hydride is one of the most promising hydrogen storage materials. However, the high desorption temperature and slow hydriding kinetics hinder the application of magnesium hydrides. To improve the hydrogen storage characteristics of magnesium hydrides, many effective treatments have been developed and applied, such as ball milling, melt spinning, alloying with other metals, adding catalysts and using thin film technique. In this work, melt spinning and alloying with Ni were the main sample modification methods used to improve hydrogen storage properties for magnesium hydrides. At the beginning of this project, it was found that it was difficult to repeat the methodology of sample preparation in the literature. Therefore, sample synthesis method was developed after numerous preliminary trials and a series of Mg-Ni alloys were melt-spun successfully. The structural characterization and analysis of hydrogen storage property were performed on the melt-spun Mg-Ni samples in a range of compositions. It was found that a nanocrystalline / amorphous structure was produced by melt spinning, and a metastable intermediate phase, Mg\(_6\)Ni, was discovered in the melt-spun materials. The melt-spun Mg-Ni ribbons exhibited fast kinetics of both absorption and desorption at 300 °C, with a high capacity. Moreover, they exhibited low temperature and even room temperature hydrogen sorption, with slow kinetics.\(\gamma\)-MgH\(_2\) phase, which forms usually under high pressure, has been found in the samples, which probably caused the ambient hydrogen absorption.