Microstructure and mechanical properties of a rotary friction welded tungsten heavy alloy

Abstract

Abstract Tungsten heavy alloys (WHAs) are widely used in many aerospace and defence applications such as radiation shields, kinetic energy penetrators etc. In the current work, attempts were made to join WHA rods (8 mm in diameter) using rotary friction welding techniques. The WHA rods were prepared via conventional liquid phase sintering and had a two phase microstructure containing tungsten particles of spherical shape and surrounded by a solid solution matrix of Fe, Co and Ni. Rotary friction welding process parameters were successfully optimized and a sound weld with a narrow weld interface without any defects was obtained. The weld interface was found to be of a uniform width of around 150 μm throughout the weld interface and showed very fine fragmented tungsten particles with a refined matrix phase. Moreover, the thermomechanically affected zone (TMAZ) elongated tungsten particles were clearly seen to react normally to the compressive force direction. Further, the heat-affected zone width was so narrow that it was not detected in the current study. Microhardness at the interface showed increased hardness when compared with the base material indicating that the microstructural refinement occurred during friction welding. Tensile tests carried out at room temperature as per ASTM-E8, showed lower strength and ductility when compared with the base material (tested along the hot-working direction). The fractography of the fractured surface of the base material and weld sample confirmed that the ductile mode of fracture had occurred.