MECHANICAL-PROPERTIES OF WHISKER-REINFORCED CORDIERITE GLASS CERAMIC COMPOSITES

Four whiskers; beta-SiC, beta-Si3N4, alpha-Si3N4 and 9Al2O3.2B2 O3, were tested as a reinforcement material of the cordierite glass ceramics. The composites containing of 10 or 30 vol% whisker and the monolithic glass ceramics were sintered by hot-pressing at 1000-degrees-C in Ar under 30 MPa for 60 min. Their sinterability and mechanical properties were investigated. Fully dense composites containing up to 30 vol% whisker were obtained, and no reaction products were observed between cordierite glass ceramics and each whisker. Bending strength, fracture toughness, elastic modulus ans Vickers hardness increased with increasing whisker content. A maximum strength of approximately 400 MPa and a fracture toughness of nearly 4.5 MPa.m1/2 were obtained for both 30 vol% beta-SiC and 30 vol% beta-Si3N4 whisker, respectively. The strength was more than twice as large and the fracture toughness was roughly 2.7 times larger than that of monolithic cordierite glass ceramics. Fracture surfaces and crack propagation behavior in these composites suggested that the main toughening and strenghening mechanisms were based on the whisker Debond-bridging and load transfer model, respectively.