Combinatorial development of high entropy-medium entropy alloy composite coating

High entropy alloys (HEAs) or medium entropy alloy (MEAs) with single-phase structure, such as either FCC or BCC, exhibits challenges in their adaptability for industrial applications due to strength-ductility trade-offs. However, similar to the hard metal design strategy, a combination of high entropy alloys in the form of composite could be a potential candidate due to its dual/multi-phase nature. Therefore, a novel HEA-MEA composite was firstly investigated through the CALPHAD approach in both equilibrium and non-equilibrium conditions, followed by experimental validation that included microstructural, mechanical and tribological analysis. The composite coating consists of harder BCC/B2-based AlCoCrFeNi HEA with a softer and more ductile FCC-based CoCrFeNi MEA manufactured using the HVOF process. The XRD results indicated the formation of BCC, B2 and FCC phase structures with the composite, which complemented the CALPHAD predictions for non-equilibrium processing conditions. The SEM and TEM results revealed no inter or intra-phase dissolution, attributing to the retention of the individuality of the different phases. The composite coating demonstrated higher hardness than either single phase AlCoCrFeNi and CoCrFeNi coatings and attained superior dry sliding wear resistance, thereby unveiling potential for industrial applications.