Boron addition has been used to refine the microstructures in TiAl castings, such as LPT blades, to improve ductility. However, boride precipitates with undesired morphologies could reduce ductility and even wipe out the entire benefit from grain refinement. Boride morphology in Ti45Al2Mn2Nb1B was found to be closely related to solidification conditions and proper processing windows have been established. In order to improve temperature capability of cast TiAl alloys to cater for the demand in new engines TiAl alloys have to be alloyed with more refractory elements, such as Nb and Ta, which will inevitably affect the boride morphologies. In this study variant alloys based on Ti45Al2Mn2Nb1B have been investigated with emphasis on the relationship between boride morphology, alloying element species and cooling conditions and distinctly different boride formation behaviour in different alloys was observed. In addition, curvy borides were found both on the fracture surface and within the microstructure in tensile test pieces, especially in Hf-containing test pieces, which indicate that curvy borides have the strongest effect in reducing ductility regardless of alloy composition.

This thesis is an investigation into a family of features that can form during the inertia friction welding of the nickel-based superalloy RR1000. A thorough characterisation of the weld features using scanning-electron microscopy has been carried out, yielding information about their composition, microstructure, morphology and their distribution within the weld zone.

The object of the work described is to determine whether, in any nickel compound, the paramagnetism of the nickel is approximately neutralised by the diamagnetism of the molecule, so that it might be possible to change the sign of the susceptibility by temperature change alone. A method for measuring small susceptibilities has been developed which, in comparison with current methods, uses simpler apparatus, and simplifies the taking of observations, without prejudice to accuracy or sensitivity. The susceptibilities of a number of nickel compounds have been investigated. It is found that the susceptibility is profoundly affected by the nature of the chemical valence link. In polar compounds the nickel retains a practically constant paramagnetism which is considerably larger than the underlying diamagnetism, and it is hence concluded that such compounds are unsuitable for investigations of change of sign of susceptibility by change of temperature alone. It is suggested that the investigation might be carried out on certain nickel dioxime compounds. The results indicate an abnormality in the structure of nickel cyanide.

This research takes the principle of localised heat treatment using inert gas jets from concept to delivery of a working prototype system and its application on a specific component. Described is the development of this technology and proof of its thermal capabilities on a number of components and test pieces. Included are discussions on the atmospheric requirements of the system and the development of the system design to minimise the formation of significant oxidation and alpha case. Finally the later sections of this thesis detail the work carried out to understand the underlying principles of this technology and how this understanding can be read across to future applications. This is done in the form of process modelling; the output of this being boundary conditions which can be used to model this technology for a number of applications and geometries in the future.

During wet-filament winding, fibre bundles are impregnated using a drum-based resin bath. The impregnated bundles are then directed to a traversing-arm prior to being over-wound onto a rotating mandrel. Once the required number of layers of the impregnated fibres has been deposited on the mandrel, the assembly is transferred to an oven to cure the thermosetting resin. After this, the composite is cooled to ambient temperature and extracted from the mandrel. There are a number of issues with the conventional manufacturing method including the generation of waste resin, utilisation of significant volumes of solvent for cleaning the equipment at the end of each shift, contamination of the factory floor due to resin drips from the impregnated tows and the cost of waste disposal. This thesis reports on the integration of a modified wet-filament winding process, which is referred to as "clean fi lament winding", into an industrial filament winding manufacturing operation. It was demonstrated that the clean filament can be utilised to address the above-mentioned issues associated with the conventional wet-filament winding. For example, an 88.12% and 87.5% reduction in solvent consumption and the generation of waste resin respectively was verified when compared to conventional wet-filament winding. Hence, it can be concluded that the clean filament winding technique is capable of producing industrially relevant filament wound composites with marginally superior or equivalent properties when compared to conventional wet-filament winding. However, the environmental benefits of the clean filament winding technique are significant.

This study, completed with the University of Birmingham, was sponsored by Controls and Data Services (CDS) and the Engineering and Physical Sciences Research Council (EPSRC). A range of materials and processes were evaluated with the aim of producing a lead-free, monolithic, machinable plain bearing to replace the leaded bronze gear pump bearings currently used. The primary alloys investigated in this thesis were Al-20Sn-7Si-1Cu and an Al-20Sn-7Si- 1Cu-1Mg wt% composition; with the latter achieved by the controlled addition of Al- 50Mg wt% master alloy. The project identified an aluminium-tin-silicon based alloy that could be sintered to near 100% of theoretical density in the manufacture of a ¾ scale rod form. The process and material produced should be capable of replacing the bearing alloys typically used in aerospace pump applications. The addition of magnesium, with controlled morphology and size, and the parallel use of a nitrogen sintering atmosphere, significantly improved the heat treated density of these materials. Successful sintering, typically completed at 500°C, could be significantly reduced in time by the use of pressurised nitrogen from 20 hours to 5 hours. The sintered microstructure generated was a heat treatable aluminium / copper matrix with desirable, discrete regions of silicon (typically 3 – 4 microns in size) and reticular tin.

Nanocomposite coatings are attractive due to their unique mechanical, physical and multifunctional properties, which can address the limitations of conventional monolithic structures to achieve an excellent combination of strength, stiffness, toughness, and some other functional properties. In this study, a novel in-situ low temperature (below 500oC) hybrid plasma technology combining active-screen plasma co-sputtering and PECVD has been developed to cost-effectively generate vertically aligned carbon nanotubes (VACNTs) films. A two-step approach has been employed to develop VACNTs reinforced composite coatings. A well-designed CNTs reinforced diamond-like carbon (DLC) composite coating can be formed using the PECVD. Besides, the Ag wires reinforced composite coatings have been deposited through a one-step approach using the advanced hybrid plasma technology combining ASP co-sputtering and plasma carburising in a plasma ambient of CH4 (1.5%) and H2 (98.5%). SEM, TEM, XRD, XPS have been applied to characterise the morphologies and microstructures of these novel composite coatings.

Fatigue crack threshold (\(D\)K\(_{th}\)) and fatigue crack growth of a near fully-lamellar \(y\)-TiAl alloy (Ti-4522XD alloy) have been investigated in air at room temperature, 400, 650, 700 and 750 oC and at three R ratios (0.1, 0.5 and 0.8). Studies were carried out on both corner-cracked specimens and smooth specimens. A combination of a \(D\)K- increasing loading method and growing a crack from notch were applied throughout the tests. As a consequence of consistent material microstructure, use of standardized testing procedure and a sufficient number of tests, some trends in fatigue threshold and crack growth have been established, including: trends include: lack of dependence of (\(D\)K\(_{th}\)) values on test temperature; average (\(D\)K\(_{th}\)) values decrease with increasing R ratio; a strong dependence of crack growth rate on K\(_{max}\) values at RT; a reduced dependence of crack growth rate on K\(_{max}\) values and increased plasticity at elevated temperatures; crack blunting causes a reduction of fatigue crack growth rate at R=0.8 and at elevated temperatures; and little effect of test temperature on ‘fracture toughness’ values. Above all, the origins of naturally initiated cracks under cyclic loading are often found to be centered on up to four colonies which have failed by interlamellar fracture.

Aluminium(Al) is widely utilised in the packaging, transportation, electrical and modern machinery sections because of its low density, high specific strength, excellent corrosion resistance, impressive electrical and thermal conductivity, abundance and recyclability. However, relatively low strength is the most significant challenge for aluminium to be applied in wider area. To solve this problem, carbon nanotube was projected as the most ideal reinforcement due to its incomparable specific strength and elastic modulus, exceptional electrical and thermal conductivity. It is assumed that carbon nanotube can not only strengthen but also introduce various distinctive characteristics into the aluminium matrix to improve its overall properties and performances. In the current research, 0.5 wt. % – 2.0 wt. % of mutil-walled carbon nanotube was ball milled with aluminium powders for 5 – 20h. The microstructure of the as-milled composite powders and as-sintered bulk composite specimens were characterized by particle size analysis, optical microscopy and scanning electron microscopy(SEM). Also, the evolution and dispersion of MWNT were studied by Raman spectroscopy and SEM. Moreover, the as-produced composites were subjected to standard Vickers hardness test and MPIF standard tensile test to investigate the mechanical properties of the composite.

The fatigue and interfacial characteristics of a unidirectional, SiC (SCS 6), fibre reinforced Ti 6Al 4V metal matrix composite have been investigated using a series of fatigue crack propagation, total life, and interfacial characterisation techniques. A room temperature crack arrest to catastrophic failure (CA/CF) transition was quantified using the initial stress intensity factor range ΔKapp. This transition occurred between 21 and 18 MPa√m in the three point bend geometry, and was found to be dependent on volume fraction of intact fibres bridging the crack. Increasing the test temperature to 300˚C had different effects on the resistance to fatigue crack growth depending on crack opening displacements and test piece stiffness. Total life fatigue tests revealed that the dominant failure mechanism was matrix fatigue cracking and fibre bridging. The extent of fatigue crack growth and fibre bridging was dependant on the applied stress and test temperature. The introduction of a dwell period at maximum load resulted in a small reduction in the total fatigue life. Post fatigue fibre push out tests identified that fatigue caused a reduction of interfacial properties below the as received levels. This reduction of interfacial properties was dependent on fatigue test temperature and initial loading conditions.