Dry Sliding Wear Behaviour of Laser Cladded AlTiSiCrCo High Entropy Alloy Coatings on Ti6Al4V: Influence of Cr/Co and Al/Ti Enrichment

This study investigated how compositional variation within the AlTiSiCrCo high-entropy alloy (HEA) system affects the microstructure, hardness, and dry sliding wear behaviour of laser-cladded coatings on Ti6Al4V. Three coatings, namely, equiatomic (HEA 1), Cr/Co-enriched (HEA 2), and Al/Ti-enriched (HEA 3), were characterized by SEM, EDS, XRD, and Vickers microhardness and tested for dry sliding wear using a ball-on-disc tribometer at 5 N and 15 N. All coatings comprise a BCC solid solution matrix reinforced by intermetallic precipitates. HEA 2 and HEA 3 gave the highest hardness (755 HV and 754 HV, respectively) against 705 HV for HEA 1 and 345 HV for the Ti6Al4V substrate. All HEA coatings reduced wear rate relative to Ti6Al4V; HEA 2 recorded the lowest rate (4.570×10−5 mm3/N.m and 2.744×10−4 mm3/N.m at 5 N and 15 N, respectively), well below the substrate (2.257×10−4 mm3/N.m and 0.0014 mm3/N.m at 5 N and 15 N, respectively). Worn surface analysis showed abrasive/delamination at 5 N transitioning to more severe abrasive, adhesive, and delamination wear at 15 N. The enhanced wear resistance of HEA 2 stems from the BCC solid solution strengthening, intermetallic reinforcement, and high chromium content, which aids in the formation of the Cr2O3 protective oxide film. Overall, enriching the coating with chromium and cobalt proved to be the most effective approach for improving the tribological performance of laser-cladded AlTiSiCrCo HEA coatings on Ti6Al4V.