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

Abstract

<p>Fabrication of fine TiN particle-dispersed dense Al<sub>2</sub>O<sub>3</sub> composites with the compositions of Al<sub>2</sub>O<sub>3</sub>/TiN=100/0~90/10 vol% has been conducted from Al<sub>2</sub>O<sub>3</sub>/(Ti,TiN<sub>0.3</sub>) mixed powder compacts by capsule-free hot isostatic pressing (HIP) utilizing high-pressure N<sub>2</sub> SHS. Fine Ti powders (φ ~ 0.3 μm) with TiN<sub>0.3 </sub>phase were prepared by thermal decomposition of planetary ball-milled fine TiH<sub>2</sub> powders at 400°C (673 K) for 1 h in a vacuum, followed by heating in N<sub>2</sub> at 200 °C (473 K) for 2 h. The Al<sub>2</sub>O<sub>3</sub> powder compacts (relative densities of 57.2-57.8%) with homogeneously dispersed (Ti,TiN<sub>0.3</sub>) particles were prepared. The mixed powder compacts were hot isostatically pressed (HIPed) under the conditions of 1350°C (1623 K) at 7 MPa N<sub>2 </sub>for 1 h, followed by the heating at the same temperature for 2 h under 196 MPa-N<sub>2</sub>. At the first stage of heating [1350°C (1623K)/7MPa/1h], solid/gas reaction of SHS between (Ti,TiN<sub>0.3</sub>) and N<sub>2</sub> was introduced to form TiN and densification of the Al<sub>2</sub>O<sub>3</sub> 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 Al<sub>2</sub>O<sub>3</sub> 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 Al<sub>2</sub>O<sub>3</sub> during HIP-sintering. Mechanical properties, such as bending strength (σ<sub>b</sub>), Vickers hardness (<em>H</em><sub>V</sub>), fracture toughness (<em>K</em><sub>1C</sub>), and electrical resistivity (ρ) of the composites were evaluated as a function of TiN content; the maximum values of σ<sub>b</sub>=640 MPa, <em>H</em><sub>V</sub>=19.5 GPa, and <em>K</em><sub>IC</sub>=4.5 MPa・m<sup>1/2 </sup>were obtained in the Al<sub>2</sub>O<sub>3</sub>/TiN=97/3~95/5 vol% composites. Among the composites, the lowest ρ value of 2.6×10<sup>3</sup> Ω・m was attained at Al<sub>2</sub>O<sub>3</sub>/TiN=90/10 vol% composite.</p>