Fabrication of TiN Particle-Dispersed Al2O3 Composites Utilizing High N2-Pressure SHS

Abstract

Fabrication of fine TiN particle-dispersed dense Al2O3 composites with the compositions of Al2O3/TiN=100/0~90/10 vol% has been conducted from Al2O3/(Ti,TiN0.3) mixed powder compacts by capsule-free hot isostatic pressing (HIP) utilizing high-pressure N2 SHS. Fine Ti powders (φ ~ 0.3 μm) with TiN0.3 phase were prepared by thermal decomposition of planetary ball-milled fine TiH2 powders at 400 °C (673 K) for 1 h in a vacuum, followed by heating in N2 at 200°C (473 K) for 2 h. The Al2O3 powder compacts (relative densities of 57.2-57.8%) with homogeneously dispersed (Ti,TiN0.3) particles were prepared. The mixed powder compacts were hot isostatically pressed (HIPed) under the conditions of 1350 °C (1623 K) at 7 MPa N2 for 1 h, followed by the heating at the same temperature for 2 h under 196 MPa-N2. At the first stage of heating [1350°C (1623K)/7MPa/1h], solid/gas reaction of SHS between (Ti,TiN0.3) and N2 was introduced to form TiN and densification of the Al2O3 powder compacts up to the relative density of 92-93% with closed pores was performed. And at the sequent second stage [1350 °C (1623K)/196MPa/2h], densification of the most of pre-sintered composites consisting of Al2O3 and TiN reached higher relative densities than 98.5%. Dispersion of TiN particles (~φ 0.30 μm) in the composites suppressed the grain growth of Al2O3 during HIP-sintering. Mechanical properties, such as bending strength (σb), Vickers hardness (HV), fracture toughness (K1C), and electrical resistivity (ρ) of the composites were evaluated as a function of TiN content; the maximum values of σb=640 MPa, HV=19.5 GPa, and KIC=4.5 MPa・m1/2 were obtained in the Al2O3/TiN=97/3~95/5 vol% composites. Among the composites, the lowest ρ value of 2.6×103 Ω・m was attained at Al2O3/TiN=90/10 vol% composite.