Swaging and heat treatment studies on sintered 90W–6Ni–2Fe–2Co tungsten heavy alloy

The effect of swaging deformation and low temperature aging on mechanical properties of tungsten heavy alloy (90W–6Ni–2Fe–2Co) was studied. The alloy was prepared by conventional hydrogen sintering followed by vacuum heat treatment and swaging with varying reductions in area (ranging from 10 to 75%). The swaged samples were aged in nitrogen atmosphere at temperatures ranging from 300 to 1100 °C followed by microstructure and mechanical property evaluation. Both microstructure and mechanical properties were sensitively dependent on the amount of deformation imparted during swaging. Subsequently, aging also influenced the properties depending upon the aging temperature. Detailed fractographic study revealed that the fracture mode of the alloy changed from intergranular to transgranular mode depending upon thermo-mechanical processing. Aging treatment after swaging affected the fracture morphology of alloy considerably. Samples aged at 500 °C showed predominant transgranular failure of tungsten grains, whereas the one heat treated at 700 °C showed increasing evidence ductile tear. Based on the results, an approach for optimizing mechanical properties that involves heat treatment and swaging operation was proposed.

► High strength of tungsten alloys associated with swaging with aging treatment. ► Size of precipitates in matrix phase decides strength and hardness of tungsten alloys during heat treatment. ► Significant change in fracture morphology of tungsten alloys, swaging followed heat treatment. ► Recrystallization of matrix yields loss of strength and gain in ductility. ► Recrystallization of tungsten yields reduction in strength.