Microstructural, mechanical and thermal characterisation of sol–gel-derived aluminium titanate–mullite ceramic composites

Aluminium titanate (AT)–mullite composites with different volume percentages of mullite were prepared using the sol–gel process. The effect of grain size and porosity on the strength, toughness and hardness of the composites was evaluated. A sintered density of 97% was obtained for a composite with 75 vol.% mullite sintered at 1500 °C and it had an average grain size of <2 μm. Strength measurements showed that increasing the amount of mullite increased the strength from 11 MPa for pure AT to 220 MPa for the AT–75% mullite composite. The strength plots were further normalised to a constant grain size of 1.25 μm and zero porosity and this analysis revealed that the as-measured composite fracture strength increased by two orders of magnitude. The thermal expansion behaviour of the AT–mullite composites was also studied.