Microstructural and Mechanical Characterization of Pressure‐Less Sintered AlN‐polytypoid Based Composites by Compositional Design

Abstract

AlN‐polytypoid materials are hard to be sintered and usually need a hot‐pressing (HP) technique and very high sintering temperatures (≥1750°C). In this study, densified AlN‐polytypoid based composites were successfully fabricated in situ via a pressureless sintering method at a relatively lower temperature of 1650°C by compositional design. Moreover, the room temperature mechanical properties of the composites were comparable with those sintered by HP method. The results showed that 15R‐based composite was sintered via a transient liquid‐phase sintering mechanism with the aid of U‐phase Sialon. The pressureless‐sintered composites were mainly composed of platelet 15R, hexagonal β‐Sialon, and intergranular U‐phase Sialon grains, which exhibited both intercrystalline and transcrystalline fracture behaviors. Partial 15R grains were of twin structure, which was found to be positive for toughening of the composites.