Spark plasma sintering behavior of TaNbHfZrTi high-entropy alloy powder synthesized by hydrogenation-dehydrogenation reaction

In this study, we successfully synthesized TaNbHfZrTi high-entropy alloy (HEA) powders using a hydrogenation-dehydrogenation reaction and investigated their sintering behavior using a spark plasma sintering method. The initial ingot had a single solid solution body-centered cubic (BCC) phase, but after annealing in the hydrogen atmosphere, it absorbed hydrogen and transformed to a metal hydride phase. At this time, the brittleness was caused, making it easy to pulverize into powder; hydrogen in the powder was then removed through a vacuum heat treatment. The dehydrogenated powders had a dual-phase microstructure composed of several tens of nm sized BCC and hexagonal-close packed (HCP) phases. After sintering the HEA powders at 1000 °C, densification was completed though the HCP phase remained and the grain growth occurred non-uniformly. In the compact sintered at 1100 °C, a single solid solution BCC phase formed as the HCP phase disappeared and grain growth occurred uniformly to form an equiaxed microstructure. When comparing the microstructures, the grain size of the initial ingot was 227.8 μm, but it significantly decreased to 22.5 μm in the compact sintered at 1100 °C. To analyze mechanical property changes induced by adopting the powder metallurgy method, compression tests were carried out. For the ingot, the yield strength was 1119 MPa, but the yield strength of the sintered compact increased to 1677 MPa due to the grain size refinement effect.