Hot-Pressing of AlN-ZrO₂(PSZ) System

Abstract

Powder mixtures of AlN and ZrO₂(PSZ), in which the amounts of ZrO₂ content were 6∼70mol%, were hot-pressed at 1200∼2000°C for 30 minutes under a pressure of 20MPa in reducing atmosphere. When the amount of ZrO₂ in the powder mixture was 33mol% (ZrO₂/AlN=1/2), all raw powders of AlN and ZrO₂ completely reacted, giving a good sintered composite material with brilliant golden colour and finely dispersed reacted products of AlON Spinel, α-Al₂O₃ and ZrN. For the systems above 33mol% ZrO₂, excess ZrO₂ (cubic phase) remained as an unreacted material, while below 33mol% ZrO₂ unreacted AlN remained. In the case of the ratio of ZrO₂/AlN=1/2, a good sintered composite material was obtained and its bending strength σ_f, toughness K_Ic, Vickers hardness H_V and Youngs modulus E were 448MPa, 2.72 MN/m^3/2, 15.3GPa, and 354GPa, respectively. ZrN, one of the reaction products, was oxidized by the heat-treatment at 750°C in air and changed to ZrO₂. This oxidation reaction of ZrN to ZrO₂ gave volume expansion of about 27%. The effect of the surface compressive stress and microcracks arising from this volume expansion on the mechanical properties of the sintered body were discussed.