Precipitation of an Intermetallic Phase in Mo-alloyed Tungsten Heavy Alloys

Abstract

This study examined the sintering phenomena of two different tungsten heavy alloys, W–8Mo–7Ni–3Fe (mass%) and W–22.4Mo–7.8Ni–3.4Fe (mass%). Experimental results revealed that extending the isothermal hold caused increase in the concentration of Mo in the liquid phase. A high concentration of Mo in the liquid phase tended to trigger the precipitation of a MoNi-type intermetallic phase at the interface between the W–Mo grains (solid solution of W and Mo) and the matrix phase. The approximate chemical formulation of this intermetallic phase is (W₄Mo₆)(Ni₇Fe₃). It was difficult to suppress the precipitation of this intermetallic phase by rapid cooling, because the phase transformation temperature of matrix phase into this intermetallic phase (1628 K) is very close to the solidification temperature of the liquid phase (1645 K).