Wear behavior and microstructural evolution of a BCC-HCP dual-phase TiZrNbMoTa refractory high-entropy alloy at room and elevated temperatures

Refractory high-entropy alloys (RHEAs) are celebrated for their exceptional yield strength and high-temperature stability, yet their wear performance remains insufficient. The wear behavior of these materials is largely governed by their deformation mechanisms and microstructural evolution during sliding. In this study, we synthesized an ultrafine-grained TiZrNbMoTa RHEA featuring a dual-phase microstructure comprised of body-centered cubic (BCC) and hexagonal close-packed (HCP) phases. This unique microstructure enhances wear resistance via the in-situ formation of gradient nanostructured layers at room temperature (RT) and fish-scale-like amorphous-crystalline nanocomposite oxide layers at 600°C during dry sliding. The RHEA shows the wear rates of 1.15 × 10⁻⁴ mm³/(N m) at RT and 9.85 × 10⁻⁶ mm³/(N m) at 600°C. At RT, a subsurface deformation layer approximately 3 μm thick developed, with the upper 1.2 μm displaying distinct nanolayered structures, while the underlying grains bent and elongated along the sliding direction. At 600°C, a protective fish-scale-like amorphous-crystalline nanocomposite oxide layer formed on the worn surface, effectively preventing direct contact between the alloy and the counterbody. This study presents a novel approach to enhancing wear resistance in BCC-HCP dual-phase TiZrNbMoTa RHEAs, highlighting the critical role of nanostructured surface layers in improving performance under sliding conditions.