Room-Temperature Strength and Fracture Toughness of β-Sialon (z=1)-SiC Composite Fabricated from Aluminum-iso-Propoxide, α-Si₃N₄ and β-SiC

Abstract

β-sialon (z=1)-SiC (50mass%) composite was fabricated by hot-pressing a spray-dried mixture of α-Si₃N₄, SiC and aluminum-iso-propoxide solution. The bending strength and fracture toughness (K_IC) of sinterd bodies were investigated by comparing with β-sialon (z=1) without SiC. Both strength and K_IC were increased from 1000 to 1560MPa and 3.5 to 4.5MPa·m^1/2 by SiC addition, respectively. About a half of tested specimens fractured from internal defects and the other fractured from surface flaws. The strength of the specimens which fractured from internal defects increased from 1180 to 1580MPa. This value coincided with that derived from the equation K_IC=σ_fY√c, due to the same size of defects as fracture origins (c). In case of the specimens which fractured from surface flaws, the strength increased from 900 to 1540MPa. The increase in K_IC presumably resulted in decreasing the size of machining flaws as fracture origins. It was considered that as the transgranular fracture occurred in the β-sialon matrix of this composite, homogeneously dispersed SiC particles immediately brought small crack deflection. This might be a reason for increase in both strength and K_IC.