Synthesis and microstructure characterization of Ni-Cr-Co-Ti-V-Al high entropy alloy coating on Ti-6Al-4V substrate by laser surface alloying

Ni-Cr-Co-Ti-V-Al high-entropy alloy coating on Ti-6Al-4V was synthesized by laser surface alloying. The coating is composed of a B2 matrix and (Co, Ni)Ti2 compounds with few β-Ti phases. Focused ion beam technique was utilized to prepare TEM sample and TEM observations agree well with XRD and SEM results. The formation of HEA phases is due to high temperature and rapid cooling rate during laser surface alloying. The thermodynamic parameters, ΔHmix, ΔSmixand δ as well as Δχ, should be used to predict the formation of the BCC solid solution, but they are not the strict criteria. Especially when Δχ reaches a high value (≥10%), BCC HEA will be partially decomposed, leading to the formation of (Co, Ni)Ti2 compound phases. •Preparing HEA coating on Ti-6Al-4V by laser surface alloying is successful.•The synthesized HEA coating mainly consists of BCC HEA and (Co, Ni)Ti2 compounds.•FIB technology was used to prepare the sample for TEM analysis.•ΔHmix, ΔSmixand δ as well as Δχ, should be all used to predict the formation of solid solution.