Phase evolution and properties in laser surface alloying of FeCoCrAlCuNix high-entropy alloy on copper substrate

FeCoCrAlCuNix (x = 0.5, 1, 1.5) high-entropy alloy (HEA) coatings were prepared on commercially pure copper (cp Cu) by laser surface alloying of Cu with Fe-Co-Cr-Al-Nix powder, aiming at improving wear and corrosion resistance. Constituent phases, microstructure, hardness, wear and corrosion resistance of the coatings were investigated using XRD, SEM, microhardness tester, friction-wear tester and potentiodynamic polarization measurements, respectively. Results showed that with appropriate laser processing parameters, crack- and porosity-free FeCoCrAlCuNix HEA coatings were obtained. The crystal structures of FeCoCrAlCuNix coatings evolved from BCC + FCC1 + ordered FCC2 structures for x = 0.5 and x = 1 to FCC1 + ordered FCC2 structures for x = 1.5. The two FCC phases possessed nearly the same lattice parameters of 3.60 Å. The ordered FCC2 phase which was deviated from the definition of HEA was enriched in Fe-Ni. The FCC1 and BCC phases agreed well with the definition of HEA. The phase formation rules of FeCoCrAlCuNix coatings indicated that besides Ω and δ parameters, solidification temperature Ts must be considered, instead of melting point as suggested previously. The microhardness of FeCoCrAlCuNix coatings decreased obviously from 636 HV to 522 HV with the addition of Ni element, which was at least 6.6 times that of cp Cu substrate (78 HV). Both the wear and corrosion resistance of FeCoCrAlCuNix coatings were significantly improved. FeCoCrAlCuNi1 coating exhibited the highest resistance to wear and corrosion among the tested samples in this study.