Pressureless sintered self-reinforced Y-α-SiAlON ceramics

Y-doped α-SiAlONs, where the level of aluminum and oxygen was varied, have been successfully densified by pressureless sintering. The effect of parameters such as starting composition, morphology of grains and sintering temperature on densification and mechanical properties of Y-SiAlON ceramics were study. It was found that Y-α-SiAlONs with different compositions could be pressureless sintered in excess of 98% theoretical density at temperatures ranging from 1750 to 1920 °C. The typical microstructure of the SiAlON investigated consists of elongated α-SiAlON grains uniformly distributed in a matrix of equiaxed grains. Fracture toughness of 6.2 MPa m1/2 and hardness of 17.6 GPa were found for Y0.667Si8.5Al3.5O1.5N14.5 (m = 2.0, n = 1.5) sintered at 1850 °C. The results indicate that both crack deflection and crack bridging mechanisms of toughening operate in the materials, with the latter being the dominant one.