Pressureless Sintered Nitride Composites in the AlN-Al₂O₃System

Abstract

Particulate nitride composites have been fabricated by sintering the compacted powder of AlN and 5-64.3 mol% Al 2 O 3 , with a small addition of Y 2 O 3 (Y 2 O 3 /AlN, 1 wt%), in 1-atm nitrogen gas at 1650-1900 o C. The composites were characterized in terms of sintering behavior, phase relations, microstructure and thermal shock resistance. AlN, 27R AlN pseudopolytype, and alminium oxynitride (AlON, 5AlN•9Al 2 O 3) were found to existin the sintered material. Regardless of batch composition, the AlN-Al 2 O 3 powder compacts exhibited similar sintering behavior; however, the degree of shrinkage commonly increased with increasing Al 2 O 3 content, consequently giving high sintered bulk density. By increasing the Al 2 O 3 addition up to ≥ 50 mol%, the matrix phase in the sintered material was converted from AlN or 27R to AlON. Above 1850 o C, a liquid phase was formed by the reaction of Al 2 O 3 with AlN, aided by Y 2 O 3 and mainly existed at the grain boundaries of AlON. Thermal shock resistance was superior in the sintered composite consisting of AlON with dispersed AlN or AlN matrix phase.