Effect of the Amount of Additives and Post‐Heat Treatment on the Microstructure and Mechanical Properties of Yttrium–α‐Sialon Ceramics

Abstract

The yttrium–sialon ceramics with the composition of Y0.333Si10Al2ON15 and an excess addition of Y2O3 (2 or 5 wt%) were fabricated by hot isostatic press (HIP) sintering at 1800°C for 1 h. The resulting materials were subsequently heat‐treated in the temperature range 1300–1900°C to investigate its effect on the α→β‐sialon phase transformation, the morphology of α‐sialon grains, and mechanical properties. The results show that α‐sialons stabilized by yttrium have high thermal stability. An adjustment of the α‐sialon phase composition is the dominating reaction in the investigated Y–α‐sialon ceramics during low‐temperature annealing. Incorporation of excess Y2O3 could effectively promote the formation of elongated α‐sialon grains during post‐heat‐treating at relatively higher temperature (1700° and 1900°C) and hence resulted in a high fracture toughness (KIC= 6.3 MPa·m1/2) via grain debonding and pullout effects. Although the addition of 5 wt% Y2O3 could promote the growth of elongated α grains with a higher aspect ratio, the higher liquid‐phase content increased the interfacial bonding strength and therefore hindered interface debonding and crack deflection. The heat treatment at 1500°C significantly changed the morphology of α‐sialon grains from elongated to equiaxed and hence decreased its toughness.