(ZrNbTiCrMo)B₂-SiC high-entropy composite coatings with promising high-temperature self-lubricating properties

High-entropy diboride ceramics are renowned for their exceptional mechanical properties, yet there remains a critical gap in the understanding of their high-temperature friction and wear performance when deployed as protective coatings. In this paper, a novel nano high entropy (ZrNbTiCrMo)B₂-SiC coating was successfully prepared through a multi-step process involving boron carbide thermal reduction, spray drying and plasma spraying process. First-principles calculations were adopted to predict the feasibility of (ZrNbTiCrMo)B₂ phase formation and its lattice parameters. The results demonstrate that SiC enhanced the microhardness and fracture toughness of the coating by approximately 20% and 30%, respectively. This improvement was achieved via densification of the microstructure, grain refinement, inhibition of Cr element segregation, and grain boundary strengthening. Specifically, from room temperature up to 900 °C, the friction coefficient and wear rate of the (ZrNbTiCrMo)B₂-SiC coating were observed to decrease with rising temperature, attaining their minimum values of 0.32 and 5.07 × 10⁻⁵ mm³/(N·m) at 900 °C, respectively. These findings indicate typical high-temperature self-lubricating characteristics. At room temperature and 300 °C, the (ZrNbTiCrMo)B₂-SiC coating was dominated by abrasive wear. At 600 °C and 900 °C, a mixed wear mechanism consisting of abrasive wear and oxidative wear was observed. The further decrease in wear rate at 900 °C stemmed mainly from the formation of shear-resistant dense oxide film, which consisted of composite nano-oxide particles encapsulated by borosilicate glass.