Effect of nano-yttria dispersion on the microstructure and mechanical properties of W-Ni-Co alloys

The effect of nano-Y2O3 (0.25-0.75 wt.%) addition in tungsten heavy alloy which consists of 93 weight percentage tungsten and Ni/Co ratio fixed at 9 was investigated. Ni, Co and Y2O3 were mixed in high-energy ball milling to obtain nanostructure and this mixture subsequently blended with tungsten (W) in a low energy ball milling. The powder mixture was consolidated by cold-isostatic pressing, and the green compact was sintered at 1,475°C for 2 hrs, followed by post annealing at 1,100°C for 1.5 hrs. W-Ni-Co alloys thus processed exhibits density greater than 96% of theoretical density. Lowest distortion of 1.5 mm was found in yttrium oxide dispersed W-Ni-Co alloy using a coordinate measuring machine. The second phase of nano-Y2O3 distributes in W-grains and matrix significantly influences grain morphology, size, microstructural features and mechanical properties. Dispersion of nano-Y2O3 enhances hardness of the matrix due to the grain refinement and formation of the inter-metallic compound.