Effect of annealing treatments on microstructure and mechanical properties of liquid-phase-sintered silicon carbide

Dense hot pressed SiC based materials were produced with alumina and yttria as sintering aids in different percentages. The microstructure and mechanical properties were evaluated on as-sintered materials and related to the starting compositions. Annealing treatments were carried out at different temperatures and holding times to evaluate the possibility of a further improvement of the material properties, above all indentation toughness and high temperature properties. The attention was focused on the microstructural modifications induced by thermal treatments, i.e. formation of elongated grains, reduction and modification of secondary amorphous and crystalline phases. Mechanical properties of the annealed materials were explained on the basis of microstructural changes and compared to those of the as-sintered materials. Annealing treatments were found to be highly beneficial for improving mechanical properties and grain boundary phase microstructural changes were found to be the main factor affecting such improvements.