Abstract: 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 comprising 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 exhibits 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 ∼3 µm thick subsurface deformation layer 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, thereby 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 RHEA, highlighting the critical role of nanostructured surface layers in enhancing performance under sliding conditions.

Key words: Refractory high-entropy alloy, BCC-HCP dual-phase, Sliding wear, Gradient nanostructured layer, Fish-scale-like oxide layer