Theoretical and Experimental Investigations of High-Entropy (TiVNbTa)2AlC MAX Phase

High-entropy MAX phases (TiVNbTa)2AlC have attracted increasing attention due to their potential advantages in structural stability, damage tolerance, and mechanical reliability under complex service environments. This work studied the crystal and electrical structures with the elastic properties, the synthesis reactions and further wear resistance of HE-MAX (TiVNbTa)2AlC theoretically and experimentally. The charge transfer between both M-C atoms and M-Al atoms turned more intense, which correspondingly strengthened the M-C and M-Al bonds, respectively. Because of the dope on M-sites, (TiVNbTa)2AlC exhibited larger fracture toughness KIC and a lower brittle index M, which suggested lower brittleness, better crack extension resistance, and higher damage tolerance than Ti2AlC. In this work, high-entropy (TiVNbTa)2AlC MAX phase ceramics were successfully synthesized by a powder metallurgy route combined with pressureless sintering and spark plasma sintering (SPS). The effects of raw material composition and sintering temperature on phase evolution, microstructure formation, mechanical properties, and tribological behavior were systematically investigated. The results show that a highly pure (TiVNbTa)2AlC phase with a phase fraction of 96.8% could be obtained at a molar ratio of M:Al:C = 2:1.2:0.8 and a sintering temperature of 1550 °C. Phase evolution analysis indicated that the reaction process followed the sequence of intermetallic compound (IMC) formation → carbide formation → MAX phase formation. Severe lattice distortion induced by the multi-principal-element solid solution significantly enhanced the hardness of the material, which was markedly higher than that of conventional ternary MAX phases. Owing to its higher hardness and more homogeneous solid-solution structure, HE-MAX (TiVNbTa)2AlC could inhibit the formation of surface microcracks and reduce the driving force for crack propagation to some extent. Therefore, the lower wear rate not only reflected improved tribological performance but also demonstrated the beneficial role of high-entropy design in enhancing resistance to surface damage.