Preparation of hypereutectic-eutectic-hypoeutectic gradient high-entropy alloy coating by in-situ interfacial reaction between Nb and FeCoCrNi.

• The hypereutectic-eutectic-hypoeutectic gradient HEA coating is prepared. • The eutectic structure in the coating is nanoscale lamellar. • Hardness of the gradient HEA coating exhibits an outside-to-inside decrease trend. • Compared with FeCoCrNi HEA coating, the surface hardness is increased by 340%. • Compared with FeCoCrNi HEA coating, the wear rate is decreased by 94.1%. In this study, a hypereutectic-eutectic-hypoeutectic gradient high-entropy alloy (HEA) coating was successfully prepared by in-situ interfacial reaction between Nb and FeCoCrNi. Its microstructure is composed of Fe-rich FCC phase and Nb-rich Laves phase, and the eutectic structure is nano lamellar. The outside-to-inside hardness of the coating gradually decreases from 797.4 Hv 0.5 to 425.5 Hv 0.5. Compared with those of the FeCoCrNi HEA coating, the surface hardness, COF, and wear rate of the hypereutectic-eutectic-hypoeutectic gradient HEA coating are improved by 340%, 41.3%, and 94.1%, respectively. The design and preparation method applied in this study can provide new ideas for the development of new HEA coatings. [ABSTRACT FROM AUTHOR]