Microstructure characterization of W-Ni-Cu heavy alloy fabricated by hydrogen reduction and pressureless sintering of WO₃-NiO-CuO powder mixture

The microstructural characteristics of the synthesized powder and sintered W-Ni-Cu alloy were analyzed. The W-7Ni-3Cu alloy was fabricated through the hydrogen reduction of ball-milled oxide powders and pressureless sintering. Microstructural observations indicated that homogeneous alloy powders with an average particle size of about 230 nm were successfully synthesized. With increasing sintering temperature, the relative density and particle size of W increase, and the resulting sintered microstructure is similar to that obtained through solid-state sintering. The sintered sample at 1200 °C had a relative density of 99.5 % and a Vickers hardness of 3.8 GPa. TEM analysis showed that the sintered sample is mainly composed of W, the binder phase of NiCu solid solution, and the Ni₄W intermetallic compound. Also, surface potential measurements using AFM-KPFM revealed the formation of a Ni₄W phase at the interface between the W grain and the binder phase. The formation of Ni₄W is explained by interdiffusion and reaction between W and Ni near the interface boundary.