Effect of annealing treatments on microstructure and mechanical propertiesof 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 mechani cal properties were evaluated on as-sintered materials and related to the s tarting compositions. Annealing treatments were carried out at different te mperatures and holding times to evaluate the possibility of a further impro vement of the material properties,, above all indentation toughness and hig h temperature properties. The attention was focused on the microstructural modifications induced by thermal treatments, i.e. formation of elongated gr ains, reduction and modification of secondary amorphous and crystalline pha ses. Mechanical properties of the annealed materials were explained on the basis of microstructural changes and compared to those of the as-sintered m aterials. Annealing treatments were found to be highly beneficial for impro ving mechanical properties and grain boundary phase microstructural changes were found to be the main factor affecting such improvements. (C) 2001 Els evier Science Ltd. All rights reserved.