A non-equimolar (Ti0.1V0.1Zr0.4Hf0.4)C solid solution: Microstructure evolution and tribological behavior from 25 to 900 °C

A single-phase, non-equimolar (Ti 0.1 V 0.1 Zr 0.4 Hf 0.4 )C carbide ceramic was densified by spark plasma sintering, and its thermomechanical and tribological behavior was systematically evaluated under vacuum from 25 to 900 °C. It exhibits high hardness, excellent thermal stability, and strongly temperature-dependent friction and wear characteristics. A pronounced reduction in wear rate occurs at the intermediate temperature of 600 °C, while the coefficient of friction decreases progressively with increasing temperature throughout the entire range. Detailed microstructural and chemical analyses of the worn surfaces and subsurface regions reveal that this behavior originates from two concurrent mechanisms: the selective segregation of vanadium (V), which forms a continuous low-shear-strength lubricating phase that remains effective in high-temperature vacuum environments above 600 °C, with the most pronounced effect at 900 °C; and the simultaneous development of a dense, thin glaze layer enriched in refractory elements that provides the most robust wear resistance at 600 °C. The optimal tribological performance across the investigated temperature window is governed by the synergistic interplay between the load-bearing protection afforded by the glaze layer and the tribo-induced self-lubrication enabled by V segregation. At 900 °C, lubrication remains operative, but the wear rate increases owing to thermal softening and the progressive instability of the oxide scale. This work identifies a coupled wear-resistance and self-lubrication mechanism, combining a refractory-element-enriched glaze layer with V-segregation-induced self-lubrication, and offers a new materials design strategy for high-performance carbide ceramics intended for extreme tribological environments.