Comparison of densification and distortion behaviors of W-Ni-Cu and W-Ni-Fe heavy alloys in liquid-phase sintering

This paper aims to correlate the densification and distortion behaviors of liquid-phase sintered 80W-14Ni-6Cu and 80W-14Ni-6Fe heavy alloys with the melting characteristics of the Ni-Cu and Ni-Fe matrices. Differential thermal analysis (DTA) of die-pressed compacts reveals that the melting range of the Ni-Cu matrix is extended from 1235°C to 1453°C by the in situ alloying between elemental Cu and Ni powders, whereas the melting of the Ni-Fe matrix is limited to a narrow temperature range between 1464°C and 1480°C. Dilatometry and furnace sintering tests show that densification due to liquid-phase sintering of 80W-14Ni-6Cu starts at 1287°C and proceeds at a low rate to 1450°C, where full densification without distortion is achieved. In contrast, densification due to liquid-phase sintering of 80W-14Ni-6Fe occurs at a very high rate above 1475°C, and full density can be obtained at 1500°C. For both alloy compacts, distortion is induced by prolonging the sintering time or elevating the sintering temperature after full densification. Crack-like voids develop in the 80W-14Ni-6Cu compact to accommodate the gravity-induced distortion, while spherical pores are dominantly formed in the 80W-14Ni-6Fe compact as a result of water vapor entrapment.