Preparation of spherical TaNbHfZrTi high-entropy alloy powders by a hydrogenation–dehydrogenation reaction and thermal plasma treatment

Abstract

Spherical TaNbHfZrTi high-entropy alloy (HEA) powders were fabricated successfully by a hydrogenation–dehydrogenation reaction and thermal plasma treatment. The HEA ingot had a single solid solution body-centered cubic (BCC) phase, and it was fully transformed to a metal hydride phase of M3H2 after hydrogenation. The hydrogenated ingot could be easily pulverized to fine powders because of its brittle nature, and the powder particles had highly irregular shapes. After dehydrogenation, the phase of the powders was separated to three phases: two BCC phases (BCC 1, BCC 2) and one hexagonal-close-packed (HCP) phase. Based on the results of the decomposition behavior of the HEA hydride, hydrogen was released in various amounts at different temperatures. Hydrogen emissions showed two peaks, the highest at 331.9 and 721.7 °C, which were related to the phase separation. The dehydrogenated powders with the irregular shapes were spheroidized by an inductively coupled thermal plasma treatment. After the plasma treatment, the HEA powders had a single solid solution BCC phase and their morphology changed to a spherical shape. Thus, with this method, spherical TaNbHfZrTi HEA powders could be fabricated successfully.