Novel nano-lamellar AlCoCrFeMn0.5Mo0.1Nbx eutectic high-entropy alloy coatings by ultrasonic assisted laser cladding: Microstructure and tribological behaviors

Eutectic high-entropy alloys (EHEAs) possess in-situ composite structure, which provides a novel strategy for developing wear-resistant alloys or coatings. In this work, a new-type AlCoCrFeMn0.5Mo0.1Nbx (x = 0.4 hypoeutectic, 0.65 eutectic and 0.8 hypereutectic) EHEA coatings were designed and prepared by ultrasonic assisted laser cladding. The design strategy, microstructure and tribological behaviors of the EHEA coatings were studied in detail. The Nb0.4, Nb0.65 and Nb0.8 coatings were all composed of BCC solid solution and Laves phase. The Nb0.65 coating showed typical nano-lamellar/nano-granular eutectic microstructure, while the Nb0.4 and Nb0.8 coatings had hypoeutectic and hypereutectic microstructures, respectively. The wear rates of the EHEA coatings (5.5 × 10−6 mm3/N·m for Nb0.4 coating, 5.3 × 10−6 mm3/N·m for Nb0.65 coating and 8 × 10−6 mm3/N·m for Nb0.8 coating) were significantly lower than those of most metallic and metal-ceramic composite materials. The wear mechanisms of Nb0.4, Nb0.65 and Nb0.8 coatings were slight adhesive wear and oxidation wear. Numerous regular rolling structures formed on the wear scar of Nb0.65 coating, which provides an anti-friction effect for the coating. The good carrying capacities and high hardness of the BCC, Laves and eutectic microstructures contributed to the excellent wear resistance of the EHEA coatings.