Phase evolution characteristics and corrosion behavior of FeCoCrAlCu-X0.5 coatings on cp Cu by laser high-entropy alloying

Fe-Co-Cr-Al-X0.5 (X = Si, Mo or Ti) powder systems with close-to-equiatomic ratios were mixed and laser surface alloyed onto cp Cu substrates, aiming at producing FeCoCrAlCu-X0.5 coatings by reaction synthesis of Cu with Fe-Co-Cr-Al-X0.5 powder. With optimized processing parameters, the laser high-entropy alloying (LHEA) coatings free of cracks and pores were achieved. X-ray diffractometry confirmed that the crystal structures of FeCoCrAlCu-X0.5 LHEA coatings evolved from two-phase fcc + bcc structures for X = Si to three-phase fcc + bcc + intermetallic structures for X = Mo and X = Ti. The phase formation analysis indicated that besides Ω and δ parameters, solidification temperature Ts must be considered when predicating on the formation of simple solid solution structure in high entropy alloys, instead of melting point of the alloy as suggested previously. The alloy for X = Si exhibited the best corrosion resistance among the tested specimens based on corrosion rate, which was two orders of magnitude lower than that of the substrate.