Effect of Nb content on microstructure and tribological properties of AlCrMoNbxNi high-entropy alloy coatings

For the surface modification of M2 high-speed steel, incorporating Laves phases into high-entropy alloy (HEA) coatings offers an innovative strategy to enhance hardness and wear resistance. In this study, a series of AlCrMoNb_xNi (x = 0, 0.25, 0.5, 0.75, and 1) HEA coatings were successfully fabricated via laser cladding. The effects of Nb content on microstructural evolution, mechanical properties, and tribological performance were systematically investigated. The addition of Nb promotes the precipitation of an Fe₂Nb-type hexagonal close-packed (HCP) Laves phase, leading to a coating microstructure dominated by body-centered cubic (BCC), B2, and Laves phases. Among the investigated coatings, the Nb0.25 coating exhibited the best tribological performance, with the lowest friction coefficient of 0.63 and wear rate of 1.49 × 10⁻⁵ mm³/N·m. Its wear resistance was approximately 2.21 times greater than that of the M2 steel substrate. The superior performance of the Nb0.25 coating originates from four key factors: First, the elliptical and needle-shaped Laves phases formed in the coating are uniformly dispersed within the BCC matrix, collectively contributing to a substantial precipitation strengthening effect. Second, the optimal ratio of Laves phases to the BCC matrix allows the coating to achieve a desirable balance between strength and ductility. Additionally, a portion of Nb is dissolved into the BCC matrix, contributing to solid-solution strengthening. Finally, the primary wear mechanism of the coating is oxidative wear, and the oxide film formed during friction effectively minimizes material loss.