The potential of post heat-treatment to improve the wear properties of nanostructured WC-Co coatings was investigated in the present study. Since the nanostructured coatings are more susceptible to the detrimental reactions during spraying than their conventional counterparts, there is certain limitation in optimization of coating properties by adjusting process parameters. Post heat-treatment of nanostructured coatings can thus offer one solution to achieve further improvement in coating performance. Nanostructured WC-Co coatings prepared by HVOF spraying were heat-treated under various temperatures and their wear properties were compared to those of the as-sprayed condition. The influence of the post heat-treatment was discussed in terms of changes in microstructure, composition and hardness of the coatings. These results demonstrate that the wear resistance of the nanostructured WC-Co coatings can be improved without any degradation of the substrate properties by proper post heat-treatment process.

SiC fibre reinforced SiAlON-MoSi2 composites have been manufactured by concurrent fibre winding and low pressure plasma spraying (LPPS), producing multi-layer, circumferentially fibre-reinforced composite rings. LPPS parameters for the powder used were optimised by a two-level experimental design method followed by additional tuning, achieving smooth sprayed surfaces with low matrix porosity and good deposition efficiency. The microstructure of the SiAlON-MoSi2 matrix consisted of a lamellar structure and uniformly distributed SiAlON splats throughout the MoSi2 matrix. The spray/wind composites exhibited 2% porosity and well controlled fibre distribution. Matrix cracking occurred after heat treatment at 1500°C and was attributed to the development of large tensile residual stresses during cooling due to CTE mismatch. Increasing the SiAlON to MoSi2 ratio in the composite solved the problem. Simulations based on residual stresses showed that the maximum permissible fibre volume fraction to avoid matrix cracking was 0.06 for SiC/MoSi2 and 0.23 for SiC/SiAlON(40v/o)-MoSi2.

A concurrent fibre winding and low pressure plasma spraying (LPPS) process has been developed to manufacture multiple fibre reinforced titanium matrix composite (TMC) rings in a single spraying operation. Optimisation of the LPPS parameters has been successively performed for two different sizes of Ti-6Al-4V powders by experimental design and statistical analysis, which provided minimum porosity and surface roughness for both powders. The most important LPPS parameters affecting porosity and surface roughness of deposits were Ar gas flow rate and chamber pressure. During TMC manufacture, the coarse Ti-6Al-4V powder spraying provided enhanced infiltration between fibres but caused degradation of fibre tensile strength, as well as a rough ring surface. The fine Ti-6Al-4V powder gave no significant degradation of fibre strength and a relatively smooth ring surface. Four-ply SiC fibre reinforced TMCs manufactured by the spray-wind process have also been evaluated in terms of porosity, fibre distribution and fibre damage.