Self-generating hierarchical lubricious phase for superior high-temperature tribological performance in multi-principal element alloys

Achieving adaptive lubrication while maintaining oxidation resistance is a key challenge in high-temperature tribological alloys. This study introduces a novel hierarchical lubricious phase in Nb-modified CoNiAl eutectic multi-principal element alloys to improve high-temperature tribological performance. The CoNiAlNb alloy exhibits a low wear rate of 1.01 × 10⁻⁵ mm³/N·m at 800 °C due to the formation of a hierarchical oxide layer, comprising Co₃O₄, NiO, AlNbO₄, and Al₂O₃. First principles calculations further reveal the formation and lubrication mechanisms of the hierarchical oxide phases. Specifically, strong Al-O bonds in Al₂O₃ form a stable and oxidation-resistant basal layer, while intermediate Al–O and Nb–O bonds in AlNbO₄ help a balance between oxidation protection and moderate shear adaptability. In addition, the weaker Co-O and Ni-O bonds in Co₃O₄ and NiO enhance self-lubrication properties. The synergistic effect of these oxides, combined with their hierarchical characteristics, presents a novel strategy for enhancing high-temperature friction performance through compositional design.