W-25%Re-HfC composite materials for Pin tool material applications: Synthesis and consolidation

The development of tool materials for high temperature applications such as friction stir welding of steels and high strength materials remain a key challenge because these materials are difficult to synthesize and consolidate by conventional means. In this work, nanostructured W-25 wt.%Re alloy and W-25Re-HfC composites of uniform microstructure containing 5 and 10 vol.% of HfC particles, were developed by mechanical alloying (MA) and spark plasma sintering (SPS) techniques. The effect of processing parameters and reinforcement content on the microstructure, densification, and properties of the developed materials was investigated. Mechanical alloying of the as-received and partially alloyed W-25 wt.%Re powder for 25 h yielded a single nanostructured solid solution with a crystallite size of 13 nm and increased its lattice strain to 0.75%. The fully alloyed powder was reinforced with 5 and 10 vol.% of HfC particles and further milled for 15 h, this led to the formation of composite powders with a uniform distribution of particles in the matrix. The uniform distribution of HfC particles, obtained by mechanical alloying, was maintained in the consolidated samples. Crystallite size of the matrix phase in the sintered composites remained in the nanometer range and did not exceed 100 nm. Partially and fully alloyed monolithic W-25 wt.%Re alloys, spark plasma sintered at 1800°C for 10 min, had relative density values of 98.2 and 97.8%, respectively. W-25Re-HfC composites containing 5 and 10 vol.% HfC, spark plasma sintered at 1800°C for 10 min, had relative density values of 96.9 and 96.2%, respectively. The composite containing 10 vol.% of HfC possessed the highest Vickers hardness value of 495.