Microstructure Dependence of Fracture Toughness and Hardness of Silicon Nitride

Silicon nitride, doped with 2.5, 5.0, and 7.5wt% MgO, was hot-pressed under various temperature-time conditions. Fracture toughness and Vickers hardness were measured, and these properties have been correlated with the fraction of β phase determined by X-ray diffractometory. Comparison with a theoretical curve confirmed that the crack deflection at rod-like crystal contributed to the increase in fracture toughness.