Microstructure and mechanical properties of FeCoCrNiNbX high-entropy alloy coatings

The microstructure and mechanical properties of high-entropy alloy (HEA) coatings by plasma cladding on Ti substrate are studied by the analysis of a series of FeCoCrNiNbX (X = 0.25, 0.6, 0.8) HEA coatings, to reveal the additional elemental Nb effects. The results show that the HEA coatings exhibit typical dendritic structure, and consist of BCC and FCC structures. The wear resistances of FeCoCrNiNbX HEA coatings increase firstly and then decrease with the increase of Nb content, agreeing with the hardness of coatings. Compared with the other HEA coatings from the previous work, the friction coefficients of the FeCoCrNiNbX HEA coatings are relatively lower and more stable, indicating the potential applications, such as for wear protection films of gear. The FeCoCrNiNb0.6 HEA coating shows high hardness and good wear resistance due to the reasonable volume fraction between BCC and FCC phases. The volume fraction of BCC and FCC structures in HEA coating are predicted not only using the valence electron concentration (VEC), but also by calculating parameters of ΔHmix and δ depending on the mixing enthalpy and the atomic size difference.