The effect of fine W particles in matrix phase on mechanical properties of tungsten heavy alloys

Tungsten heavy alloys 90W-7Ni-3Co (WNC) and 89.6W-6.2Ni-1.8Fe-2.4Co (WNFC), produced using liquid phase sintering followed by thermo-mechanical processing, were investigated for microstructure and mechanical properties. 90W-7Ni-3Co alloy processed following a cyclic heat treatment showed fine tungsten particles in the matrix. The alloy, when heat treated at a temperature 850°C (the lower temperature of cyclic treatment), formed a W-rich intermetallic phase in the matrix that subsequently dissolved during high temperature (1150°C) solution treatment leaving behind fine W particles. On the other hand, the matrix phase of the alloy, 89.6W-6.2Ni-1.8Fe-2.4Co showed a clean structure devoid of any such precipitates. Both the alloys were subjected to a thermomechanical treatment that included two stage swaging with intermediate heat treatments. 90W-7Ni-3Co alloy exhibited superior strength, but lower elongation to failure and impact toughness as compared to 89.6W-6.2Ni-1.8Fe-2.4Co alloy. Microstructure-property correlation was undertaken in order to elucidate the effect of enhanced W dissolution and fine W precipitates (in the matrix) on mechanical behaviour of the alloys investigated.