Characteristics of densification and distortion of Ni–Cu liquid-phase sintered tungsten heavy alloy

The characteristics of densification and distortion of a 80W–14Ni–6Cu alloy during liquid-phase sintering (LPS) were investigated in relation to the liquid-phase formation. By means of differential thermal analysis (DTA), the melting process of the Ni–Cu matrix in a die-pressed compact was examined and compared with that in a loose powder mixture. It was revealed that enhanced inter-diffusion and in situ alloying occur between the tightly compacted elemental Cu and Ni powders during heating, leading to an extended temperature range for Ni–Cu liquid formation. Dilatometry and furnace sintering tests showed that the early melting of the Ni–Cu matrix results in an onset of liquid-phase sintering at a lower temperature with die compaction. Full densification of the compact, together with satisfactory microstructure, can be achieved prior to full melting of the Ni–Cu matrix. Distortion is delayed until the end of liquid-phase formation.