Effect of Grain Size of β-Si_3N_4 and Glassy Phase on Strength and Fracture Toughness of In-Situ Toughened Si_3N_4

摘要

An in-situ toughened Si3N4 ceramic is obtained by hot-pressing.Its flexural strength andfracture toughness are 960MPa,12.74MPa·m1/2at room temperature and 720MPa,23.94MPa·msub>1/2at 1350℃,respectively.The relation between grain size of β-Si3N4 and mechanicalproperties is investigated.The glassy phase containing Y and La plays an important role inincreasing high-temperature mechanical properties because of its high viscosity and softeningtemperature.Crack deflection,crack branching and pullout of rodlike β-Si3N4 grains are ob-served in this material by SEM,and the toughening mechanisms are discussed.