Microstructure and Electrochemical Corrosion Behavior of Laser Cladding (CoCrNiFeMo)91.5B6.0Si2.5 High‐Entropy Alloy Coating on TC4 Titanium Alloy

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(CoCrNiFeMo)91.5B6.0Si2.5 high‐entropy alloy (HEA) coatings are deposited on TC4 titanium alloy by laser cladding, and their microstructure and properties are investigated. The findings indicate that FCC1 and FCC2 are dendritic and euqiaxed structures, respectively, and that HEA coatings form a FCC + σ eutectic structure. A strong metallurgical bond and a high density interface fusion layer are created at v = 1200 mm min−1, and the laser energy density matches that of the cladding. The thermodynamic criteria for the FCC + σ eutectic phase in HEAs created by the nonequilibrium solidification are proposed as follows: δ ≤ 8.5%, 6.88 ≤ VEC ≤ 8, −17 ≤ ΔHmix ≤ 7 kJ mol−1, and PSFE ≥ 40 at%. The thermodynamic parameters of HEACs are as follows: δ = 8.46%, ΔHmix = −10.282 kJ mol−1, VEC = 7.2, and PSFE = 43 at%, which meet the criteria. The coating's cross‐sectional hardness gradually drops from HEA‐coating‐zone, fusion‐zone, heat‐affected zone, and TC4 matrix. When v = 1200 mm min−1, the HEA‐coating‐zone has the highest mean microhardness (830.96 HV1.0). HEA coatings have a double passivation zone with the highest Ecorr (−0.1774 V) and a much lower Icorr (0.047 μA cm−2) than that of other scanning rates. Its FCC + σ eutectic structure, greater crystallinity, improved passivation effect, more dense microstructure, and fewer lattice and grain boundary defects all work together to provide its exceptional electrochemical corrosion performance.