Simultaneous Synthesis and Sintering of Al2O3/TiN Composites using Capsule-free N2-HIPing from Al2O3 and Fine Ti mixed Powder Compacts

Abstract

Synthesis of dense composite materials with the compositions of Al2O3/TiN=100/0∼90/10 vol% has been attempted directly from Al2O3/Ti mixed raw powder compacts using capsule-free N2 hot isostatic pressing (HIP). Fine Ti powders (0.3 μm in diameter) with a small amount of TiN0.3 phase were prepared by thermal decomposition of fine TiH2 powders at 400°C for 3.6×103 s in a vacuum, followed by thermal treatment in N2. Then, Al2O3/Ti mixed powder compacts with homogeneously dispersed Ti particles were fabricated and then HIP-sintered. During the first stage of HIPing [1350°C/6 MPa/3.6×103 s], solid/gas reaction between Ti and N2, in which both were contained in the powder compacts, was introduced to form TiN. Then, after the successive second stage of HIPing [1350°C/196 MPa/7.2×103 s], the most of sintered composites consisting of Al2O3 and TiN phases reached to a higher relative density than 98.5 % with closed pores, nevertheless a capsule-free HIPing. Dispersion of TiN particles (0.30∼0.35 μm) just formed suppressed the grain growth of Al2O3 during sintering. Mechanical properties, such as bending strength (σb), Vickers hardness (HV), and fracture toughness (KIC) have been evaluated as a function of TiN content.