Fabrication, Characterisation and Properties of Alumina Matrix Nanocomposites

Alumina/silicon carbide and alumina/titanium nitride nanocomposite materials have been fabricated by the mechanical mixing of sub-300 nm starting-powders. A brief description of the processing methods is given with particular emphasis on improvements incorporated during the milling and drying steps in order to achieve a dense microstructure and a homogeneous dispersion of nanoparticles throughout the matrix. The presence of the second-phase particles hindered densification and grain growth, but this effect was less pronounced in the case of TiN. The results suggest that the properties of the particle/matrix interface are dominant in determining the extent of the inhibition. The addition of SiC particles to the alumina matrix decreased the propensity for fracture along the grain boundaries. This was accompanied by an increase in fracture strength of up to 30% and a reduction in wear rate by a factor of three. In contrast the addition of TiN particles into the matrix did not change the fracture mode from intergranular to transgranular, and caused a decrease in fracture strength of approximately 35%. These results are discussed in terms of the internal stresses generated by the nanoparticles.