Nb-controlled eutectic microstructure evolution and property optimization in laser-cladded AlCoCrFeNi2.1Nbx coatings

AlCoCrFeNi 2.1 Nb x (x = 0, 0.6, 0.8, 1.0, and 1.2) high-entropy alloy (HEA) coatings were fabricated on 316L stainless steel by laser cladding, and the effects of Nb addition on the solidification behavior, microstructural evolution, and properties have been systematically investigated. The results indicate that Nb addition significantly modifies the solidification pathway, evolving from “L → B2 → FCC/Laves eutectic” to “L → FCC/Laves eutectic” and finally to “L → Laves → FCC/Laves eutectic”, thereby driving a continuous hypoeutectic-eutectic-hypereutectic microstructural transition. Transmission electron microscopy (TEM) analysis verifies that the fully eutectic microstructure consists of refined FCC/Laves lamellar colonies. Accordingly, the microhardness increases significantly from 352.90 HV to 857.81 HV which is attributed to the increasing fraction of the hard Laves phase. However, the best wear resistance is achieved in the Nb0.8 coating which is likely associated with the combined hardness-toughness combination of primary B2 phases and the eutectic structure. Electrochemical results suggest that Nb changes the corrosion damage mode from severe localized corrosion in the FCC/B2 dual-phase structure to a more uniform mode in the FCC/Laves eutectic structure. Overall, Nb appears to regulate the mechanical and corrosion behaviors of AlCoCrFeNi 2.1 Nb x coatings through solidification-pathway regulation, suggesting close correlations between composition, solidification behavior, microstructural evolution, and property responses.