Metal matrix composites (MMCs) have been used in many applications (such as automotive, aerospace and construction) for many decades. Recently, there have been interesting developments in this type of composite, applying them in electronic and thermal applications such as with semiconductors, in electronic packaging and heat sinks. This is particularly the case for composites of a metal matrix with diamond which are considered a modern sub-class of metal matrix composites. However, while the thermal properties are exceptional, this class of composites has not been extensively examined for mechanical and tribological behaviour, and it may be possible to apply these composites in practical applications, especially those that require extreme mechanical and tribological strength, for example cutting resistance for security applications. Therefore, this research looks for a composite material consisting of metal matrix and diamond particles, which resists abrasive cutting. This progresses through a series of steps, developing methods to process the material, understanding the mechanics of abrasive behaviour and optimizing the composite structure to resist abrasive cutting. Gas Infiltration (GI) casting under gas pressure has been applied to metal matrices with relatively low melting point (aluminium (Al) and tin (Sn)) to obtain a significant penetration of the metal into a preform of diamond particles. Different diamond particle sizes (63-75, 212-250, 420-500 μm) were used to strengthen the Al matrix and diamond coated with a thin Ti layer was used to attempt to enhance the bonding forces between the aluminium matrix and diamond. Al-1 wt. % Mg as a matrix alloy was utilised to investigate the possible effect of Mg on bonding phases and to reduce the surface tension of molten aluminium during the infiltration process. Epoxy was also used as a matrix with diamond in this research by gravity infiltration. Tribological and microstructural tests were performed on the samples, and the results show that the surface modification (Ti coating) of diamond particles has an important role for enhancing the bonding between the aluminium matrix and diamond reinforcement as is apparent under SEM observation, thus improving wear resistance. The coating layer works to either catalyse the graphitisation of diamond surfaces to then dissolve carbon in the metal, or reacts at the diamond surfaces to form carbide crystallites at the interface. This may be one of the reasons contributing to the bonding between the different matrices and diamond. The presence of some of these phases was indicated with XRD patterns and Raman spectra. The principal characterization method was by abrasion cutting tests, which have been carried out on all the samples made. One particle size range, 420-500 μm, of diamond coated by Ti, has been used to manufacture composites with different matrices (titanium (Ti), nickel )Ni(, copper)Cu(, tin)Sn) and epoxy) using different production methods (PM and SPS) for the transition metal matrices due to their high melting points. The abrasion cutting tests of these composites showed that the bonding between the metal matrix and diamond reinforcement and the processing temperature, have an important role in enhancing the abrasion wear resistance of composites, rather than the hardness of matrices.

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Minimization of propeller cavitation noise is best achieved through accurate and reliable pre-dictions at an early design stage. The effect of cavitation and particularly the dynamics of cav-itation on URN is rather complex to understand and the current state of the art does not offer a plausible cavitation noise prediction method which can be implemented within the propeller design spiral. Within this framework, the aim of the present thesis is to enhance the understand-ing of the propeller cavitation noise by conducting detailed systematic cavitation tunnel tests to investigate the main propeller design parameters and operating conditions and to scrutinize their impact on propeller Radiated Noise Levels (RNL). The resulting experimental data are also utilized to compile a database that enables engineering a novel noise prediction method to be developed and used at preliminary design stage, using standard series approach. A holistic approach to cavitation noise has been adopted through experimental investigations into oblique flow effects on propeller noise and by conducting full scale and model scale noise experiments of a research vessel. These have been used to evaluate the capabilities of the adopted standard series based experimental prediction methodology. The accumulated knowledge based on prior experiments has been utilized to design standard series propeller test campaign. Experiments using members of Meridian standard propeller se-ries were tested both in an open water condition and also behind systematically varied wake inflows. Initially, a small subset of the Meridian standard propeller series was chosen, with loading conditions derived from in-service, ocean-going vessels. The resulting measured noise data were extrapolated to full-scale based on the powering information of these vessels to com-pare with average shipping noise data. Finally, a larger subset of the propeller series was tested systematically to compile a database of propeller cavitation noise and for the development of noise prediction software.

In the present work, the relationship between the microstructure and the corrosion behaviour of Al-Cu-Mg and Al-Cu-Li alloys with various thermomechanical conditions has been studied. The microstructural characterization of the AA2024-T351 Al-Cu-Mg alloy revealed that the constituent intermetallic particles, assigned as S-phase (Al2CuMg), θ-phase (Al2Cu) and alpha-phase (Al-Cu-Fe-Mn-(Si)), are present individually or together as clusters. Further, precipitates along with Mg/Cu segregations were detected along the grain boundary network. It was also revealed that the cold working to obtain T351 temper resulted in the heterogeneous distribution of grain-stored energy. It was revealed that selective dissolution of Mg from the S-phase particle results in the copper-rich S-phase remnant, which contributes to the conversion of its electrochemical property. As a result, the micro-galvanic coupling between the S-phase remnant and the alloy matrix leads to the development of trenching at its adjacent. Trenching was also found in the periphery of the θ-phase particle and the alpha-phase particle, due to their more positive electrode potentials relative to that of the alloy matrix. Further, selective dissolution also occurred in the θ-phase and alpha-phase particles, resulting in the development of porous banding structure along certain orientation. Localized corrosion in the AA2024-T351 aluminium alloy preferentially propagated in the form of intergranular corrosion at the early stage of the exposure to sodium chloride solution. The distribution of grain-stored energy significantly affects the development of intergranular corrosion. With prolonged exposure time, localized corrosion propagated selectively into grain interior, resulting in the development of crystallographic pits. In the corrosion front area, the necessary chemical condition (low pH and chloride rich) was generated and maintained. Meanwhile, a copper-enriched layer beneath the corrosion product layer acted as an effective cathode to support the anodic dissolution. Therefore, the anodic dissolution of aluminium at the corrosion front is self-supported. The 2A97 Al-Cu-Li alloys in different thermomechanical conditions exhibited different amounts and distributions of T1 phase (Al2CuLi) precipitates since the pre-ageing cold working and the ageing condition significantly affect the T1 phase precipitation in Al-Cu-Li alloys. Further, the different thermomechanical histories also resulted in significantly different grain structures in the alloys. The corrosion morphology of the 2A97 alloy is closely associated with the distribution of T1 phase precipitates. In the T3 condition, attacked grain boundaries are the dominant corrosion features since T1 phase precipitates distribute along selective grain boundaries. In the T4 condition, localized corrosion propagated in the form of intergranular corrosion and developed into the grain interior with prolonged immersion time, related to the distribution of T1 phase precipitates. In contrast, crystallographic pits are evident in the grain interior of 2A97-T6 alloy due to the high population density of matrix T1 phase precipitates. Both grain interior and grain boundary were selectively attacked in the 2A97-T8 alloy during the immersion testing, which is consistent with the T1 phase precipitates distribution. Further, it was also found that the selective corrosion behaviour in the 2A97 Al-Cu-Li alloys is closely associated with the heterogeneous distribution of grain-stored energy, with high localized corrosion susceptibility corresponding to high level of stored energy.

Dissimilar welding of Al to Mg alloys could potentially find significant application in the automobile industry, if the massive production of brittle intermetallic compounds (IMCs) at the joint interface can be prevented. In order to better understand Al-Mg IMC reactions, a comprehensive investigation of the interfacial region in AA6111 - AZ31 diffusion couples was carried out in this research. Three Al-Mg binary IMCs, namely the -Al12Mg17, -AlMg and -Al3Mg2 phases, were observed to form in the Al - Mg diffusion couple. In both the Al3Mg2 and Al12Mg17 layers, residual stresses were detected. The stress components normal to the joint interface were found to be positive, which had the effect of promoting the extension of lateral cracks; while the horizontal components were compressive, which could hinder cracking in the vertical direction. As a result, the fracture resistance of the two IMCs were asymmetric with lower values along the interface than in the vertical direction. The higher stress level in the Al3Mg2 layer made it more susceptible to lateral cracking and hence becoming the weak link in the Al - Mg dissimilar joints. A potential metallurgical solution has been explored involving the introduction of Zn into the material system, so that a new intermetallic compound with better properties can be formed to replace the unfavored Al3Mg2 phase. In this research, an Al-Zn coating alloy was proposed for this purpose. To determine the optimum composition for the alloy, a numerical method that combined CALPHAD thermodynamic calculation and diffusion simulations was developed. The modelling results indicated that Al-20 at. % Zn was the optimum composition for completely suppressing the formation of Al3Mg2, and this has been verified by static diffusion and friction stir spot welding (FSSW) experiments. In both cases, the designed coating alloy was effective in changing the Al-Mg reaction path by forming the mechanically superior (Al,Zn)49Mg32 phase as a substitute for Al3Mg2. The FSS welds prepared with the Zn containing coating alloy exhibited a 6 % increase in lap shear strength, compared to the conventional Al-Mg welds. This lower than expected improvement resulted from the Zn addition reducing the liquation temperature of the material system, resulting in the production of a detrimental eutectic mixture which facilitated debonding of the welds. As a potential alternative solution, Al-Si coating material has been proposed to inhibit the growth of Al-Mg IMC layers, in which the Si phase was expected to form a partial interdiffusion barrier between the substrate materials and change the reaction path by preferentially reacting with Mg. Comparison of long-term static diffusion experiments between the Al-Si coated and Al - Mg dissimilar joints showed that the nucleation and growth of Mg2Si could change the reaction path and greatly reduce the thickness of the Al-Mg IMC layer at the joint interface. Although in actual friction stir spot welding (FSSW), Mg2Si was not formed in a detectable amounts, due to the very short reaction time, the Al-Si coating still led to a significant reduction in the IMC thickness by partially blocking the Al-Mg interdiffusion process. With the coating applied, the Al - Mg dissimilar welds exhibited enhanced mechanical performance with both their strength and fracture energy being markedly increased, through a reduction in the IMC layer thickness and the presence of Si particle toughening the reaction layer by causing crack deflection.

Chemical treatments of hair, especially bleaching, affect the inner and outer hair structure due to oxidative damage reactions. Several aspects of these damage effects are investigated. An optical evaluation system is developed to characterise the surface properties of unbleached and bleached hair in an uncontrolled in vivo study by means of confocal laser scanning microscopy. Bleaching leads to deformation of the scale edges, distances between scale edges and other surface phenomena e.g. residues. A rougher surface of bleached hair compared to unbleached hair is observed by using the automatic measuring software of the confocal laser scanning microscope. The influence of natural hair colour, length of hair, as well as heat styling or hair care rituals on the contact angle and tensile properties of hair is determined as well. Particularly bleaching affects both the inner and outer properties. In a controlled in vitro study the influence of bleaching on the inner hair structure is analysed by means of DSC and tensile measurements. Ultra bleaching and medium bleaching of hair lead to a direct decrease in denaturation temperature (TD). By monitoring TD over a period of six months a significant increase is observed. While the denaturation enthalpy of hair decreases directly after ultra bleaching, the enthalpy after medium bleaching is slightly higher compared to virgin hair. Similar effects can be observed by performing tensile measurements, which also show a strengthening after six months. The DSC results as well as those of tensile properties show a continuous change of the inner hair structure after bleaching, presumably due to an ionic rearrangement mainly in the matrix. The hair regains thermo-stability as well as mechanical stiffness. Differences in swelling behaviour as well as surface shrinkage phenomena after DSC also indicate changes in the matrix depending on the storage time after bleaching. The low denaturation temperature directly after bleaching can be increased again by a 24-hour dialysis of hair, which eliminates remaining ions of the bleaching product. However, the denaturation temperatue of hair depends mainly on the pH-value of the treatment: the lower the pH-value the higher TD. Therefore TD of bleached hair can be increased by a chelating agent treatment at pH 4.6 as well. The positive impact of EDTA is presumably caused due to its buffer action, which stabilises an acidic adjusted pH-value equal to the isoelectric point of hair, which results furthermore in lower swelling of hair.

Electrochemical supercapacitors are promising devices for energy storage applications. However, their uptake is currently limited by their relatively low energy density. The recent discovery of graphene has strengthened supercapacitor research, due to graphene's high surface area, conductivity, strength, and flexibility. However, the synthesis of large quantities of defect-free graphene and its subsequent incorporation into supercapacitors has proved difficult due to aggregation and restacking of the graphene. Hence, in order to retain the high surface area of graphene, it needs to be incorporated into hierarchical structures. Given these issues, this thesis aimed to produce high quality graphene flakes via electrochemical exfoliation. These flakes were then processed into hierarchical structures (foams and fibres) for supercapacitor devices. The graphene was exfoliated using a reductive process, with two different cells designs explored. The influence of the microstructure of the initial graphite on the exfoliation process was also studied. The hierarchical foams were produced by depositing the graphene onto nickel foam. It was found that the degree of exfoliation has a marginal effect on the capacitance of the device. This electrochemically exfoliated graphite was also wet-spun with polyacrylonitrile (PAN) and carbonised to produce carbon fibre-graphene composites. It was found that the carbonised materials had a higher capacitance than the precursor material (33 F g-1 and 47 F g-1 respectively). As a comparison, wet-spun graphene oxide fibres were synthesised with polyvinyl alcohol and were subsequently carbonised and reduced. These fibres gave comparable capacitance results to the carbonised polyacrylonitrile fibres (47 F g-1 and 40 F g-1 respectively).

In modern gas-turbine engines, thermal barrier coatings (TBCs) are used to provide thermal protection for the underlying metallic components. In this thesis, 3D X-ray micro-computed tomography (μ-CT) has been applied to characterise TBCs, with an attempt to non-destructively track their microstructure degradation and correlate their thermal conductivity with their microstructural details. TBCs deposited via electron-beam physical vapour deposition (EB-PVD) with a β-Ni(Pt)Al bond coat have been widely used in high-pressure turbine blades for aeroengines. Using destructive characterisation techniques, it has been found that multiple degradation processes occur simultaneously during thermal cycling. However, no direct tracking of the degradation during thermal cycling at the same sample position has been reported. Therefore, the microstructure degradation process of an EB-PVD TBC with a β-Ni(Pt)Al bond coat during thermal cycling at 1150 °C was followed non-destructively using X-ray μ-CT. The feasibility of X-ray μ-CT is validated by cross-sectional SEM micrographs of a reference sample subjected to the same thermal cycling test. X-ray μ-CT results are in accordance with the predictions from the TGO growth mechanisms and the ratcheting mechanism for TGO undulation evolution. The thermal conductivity of an air-plasma sprayed (APS) TBC is studied. Meanwhile, microstructurally realistic models are developed from μ-CT virtual slices of the same sample. It is found that inter-splat cracks and interfaces can significantly reduce the thermal conductivity of the coating. Sintering at 1100 °C for 10 h leads to a thermal conductivity comparable to the predictions from image-based models. This suggests that in the long run, the effective thermal conductivity is determined by the pores revealed by X-ray μ-CT. The shape of the pores is found to be dependent on their volume. The larger the pore, the higher its aspect ratio is. In addition, the larger pores are more preferentially aligned to the coating's spray direction. As a result, the volume averaged thermal conductivity reduction is higher for pores with a bigger volume. As a potential candidate to the self-healing TBC material, the fracture toughness of an YSZ ceramic embedded with 20 vol. % MoSi2 prepared by sparking plasma sintering (SPS) is studied. Four-point bending test and digital image correlation (DIC) give comparable fracture toughness values of ~ 2 MPa√m. The crack/particle interaction is revealed by DIC. It is found that the crack tends to cut through the particle/matrix interface. Defects (i.e. pores) at the interface is found. In addition, the residual stress induced by the misfit in thermal expansion coefficients leads to a local tensile hoop stress around the particle. These two factors are responsible for the predominant interfacial cracking.