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 AlCoCrFeMn(0.5)Mo(0.1)Nbx (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 Nb-0.4, Nb-0.65 and Nb-0.8 coatings were all composed of BCC solid solution and Laves phase. The Nb-0.65 coating showed typical nano-lamellar/nano-granular eutectic microstructure, while the Nb-0.4 and Nb-0.8 coatings had hypoeutectic and hypereutectic microstructures, respectively. The wear rates of the EHEA coatings (5.5 x 10(-6) mm(3)/N center dot m for Nb-0.4 coating, 5.3 x 10(-6) mm(3)/N center dot m for Nb-0.65 coating and 8 x 10(-6) mm(3)/N center dot m for Nb-0.8 coating) were significantly lower than those of most metallic and metal-ceramic composite materials. The wear mechanisms of Nb-0.4, Nb-0.65 and Nb-0.8 coatings were slight adhesive wear and oxidation wear. Numerous regular rolling structures formed on the wear scar of Nb-0.65 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.