Optimizing the potential of AlCoCrFeNi high-entropy alloy: EHLA-driven composite coating for tribological applications

The AlCoCrFeNi high-entropy alloy (HEA) has received considerable attention due to its single-phase body-centred cubic (BCC) solid-solution microstructure, which results in an exceptional combination of hardness and wear-resistant properties. Recent advancements in coating technologies, particularly extreme high-speed laser material deposition (EHLA), present new opportunities for HEAs. EHLA's low heat input and high deposition rates result in reduced substrate dilution, uniform chemical distribution, and minimized elemental segregation, producing dense and crack-free coatings. While the combination of AlCoCrFeNi and EHLA holds great promise for creating wear-resistant coatings in industrial applications, the brittle nature of AlCoCrFeNi HEA often leads to significant cracking, limiting its potential. Therefore, a composite coating combining a hard BCC/B2-based AlCoCrFeNi HEA with a softer, more ductile FCC-based CoCrFeNi medium-entropy alloy (MEA) was developed, resulting in near-crack-free, dense EHLA coating with enhanced mechanical performance. Microstructural and nano-mechanical analyses, including SEM, EBSD, and nanoindentation mapping, revealed variations in localized properties across phases. Scanning wear tests showed superior nanowear resistance of the composite coating compared to steel substrate and Ni-superalloy interlayer. The EHLA process thus offers promising potential for the development of next-generation HEA coatings for engineering applications.