Effect of Powder Preparation Method on the Microstructural Characteristics of Sintered W-7Ni-3Cu Heavy Alloy

The effect of powder characteristics and sintering temperature on the properties of W-7Ni-3Cu is investigated. The heavy alloy powders were prepared by ball milling and hydrogen reduction of elemental metal or metal oxide powders. Microstructural analysis revealed that the powder mixtures reduced by hydrogen at 800oC consist of a trace amount of Ni4W phase along with the metal W phase and Ni-Cu solid solution. Additionally, compared to metal powder, the powder mixture using oxide as raw material exhibited a relatively fine particle size. The W-7Ni-3Cu alloys sintered using oxide powders had relative density of over 99%, whereas the specimens using metal powders as a raw material showed relatively low values of 87.8~98.2%. The Vickers hardness of the sintered specimens using oxide powder was 3.34–3.92 GPa, which was higher than that of 2.39–3.22 GPa measured when using metal powders. The observed results can be attributed to the relatively high density and the reduced grain size.