Reaction sintering fabrication of (AlN, TiN)–Al2O3 composite

The (AlN, TiN)–Al2O3 composites were fabricated by reaction sintering powder mixtures containing 10–30 wt.% (Al, Ti)–Al2O3 at 1420–1520°C in nitrogen. It was found that the densification and mechanical properties of the sintered composites depended strongly on the Al, Ti contents of the starting powder and hot pressing parameters. Reaction sintering 20 wt.% (Al, Ti)–Al2O3 powder in nitrogen in 1520°C for 30 min yields (AlN, TiN)–Al2O3 composites with the best mechanical properties, with a hardness HRA of 94.1, bending strength of 687 MPa, and fracture toughness of 6.5 MPa m1/2. Microstructure analysis indicated that TiN is present as well dispersed particulates within a matrix of Al2O3. The AlN identified by XRD was not directly observed, but probably resides at the Al2O3 grain boundary. The fracture mode of these composites was observed to be transgranular.