Microstructure control of in-situ-toughened alpha-SiAlON ceramics

Abstract

Single-phase alpha-SiAlON with elongated grains is obtained from alpha-Si3N4 powder for a broad range of compositions of practical interest. Following the concept of nucleation and growth, two-step firing is used for microstructure control. This method takes advantage of the slow transformation reaction from alpha-Si3N4 to alpha-SiAlON at low temperature when the composition is near the alpha-SiAlON phase boundary and, hence, is marginally stable. For more-stable compositions, the seeding of alpha-SiAlON crystals is more effective, because it allows elongated grains to growl onto the seed crystals. The fracture toughness is strongly correlated with the microstructure and is enhanced greatly in the optimized materials.