Preparation for WC-Ni₃Al Hard Metal by Vacuum Sintering

Abstract

WC-Ni₃Al hard metal of the composition for WC-25 vol% (Ni-24 at%Al-0.5 at%B) was prepared by vacuum sintering. The powder mixtures of WC, Ni, NiAl (Ni-50 at%Al) and B were treated by wet milling with tumbling ball mill machine for 24 hr and 48 hr. The average particle size of the powder mixtures after wet-milling for 24 hr and 48 hr were 1.69 μm and 1.23 μm, respectively. These powder mixtures were press-molded into the test-piece and sintered in vacuum of (7~9) × 10⁻³ Pa at various temperature for 1 hr. The densities, microstructures and mechanical properties of the obtained sintered compacts were investigated. When 48 hr wet-milled powder was used and the green compact was sintered at 1425°C for 1 hr, the compact had a relative density more than 99%, transverse rapture strength of 2.2 GPa and vickers hardness of 1330 HV. On the other hand, using 24 hr wet-milled powder, the sintered compact had lower mechanical properties than the compact of 48 hr wet-milled powder due to low density and inhomogeneous microstructure.