HOT-PRESSING OF TIN-ALUMINA COMPOSITES

The hot press sintering of ultrafine gamma-Al2O3-TiN and theta-Al2O3-T iN composites was studied. Initial materials were prepared by the hydr olysis of ultrafine AlN-TiN composite powder with the followed preheat ing at 450-degrees-C in vacuum and by mixing theta-Al2O3 and TiN powde rs, all made by the RF plasma chemical synthesis. The hot pressed samp les were dense with no observable open porosity. Even when sintered at a temperature as low as 1500-degrees-C, the composites exhibited good strength, hardness and fracture toughness. The highest bending streng th values were 481 +/- 30 MPa for the hydrolyzed and 472 +/- 60 MPa fo r the mixed composites. Both composites differ by phases content and c hanges in lattice parameters of alpha-Al2O3 and TiN. This is due to th e different water content in initial aluminas used, gamma-Al2O3 and th eta-Al2O3, which resulted in different oxidation states of Ti for the mixed and hydrolyzed composites. The enlargement of the Al2O3 and TiN unit cells caused by the dissolution of Ti2O3 and TiO, results in the lattice softening which together with the other characteristics, is an important factor governing the mechanical properties of sintered comp osites.