Microstructure and properties of laser cladding NiFeCrCoMo high entropy alloy coating on the surface of TP347 steel

The laser cladding NiFeCrCoMo high entropy alloy coatings (HEACs) were prepared on the surface of TP347H steel. The microstructure, phase formation, microhardness, and electrochemical corrosion performance were investigated. The result shows that the coating exhibits a single FCC structure, with a cross-sectional structure composed of matrix, heat-affected-zone (HAZ), fusion-zone (Fz), and HEA-coating-zone (HEACz). The Fz structure is a mixed crystal structure with dense columnar crystals and equiaxed crystals. The HEACz and surface of the coating are both composed of dendritic structures. Mo is enriched within the dendrites. The average hardness of the coating is 455.75 HV1.0, which is approximately 2.26 times that of TP347 steel. The thermodynamic parameters of the HEA coating include the following: ΔH_mix= − 10.28 kJ/mol, ΔS_mix= 15.07 J/kmol, δ = 8.46%, Ω = 2.19, meeting the conditions for the formation of a single FCC stable solid solution in a multiprincipal component high entropy alloy under nonequilibrium solidification conditions. Compared with TP347H steel, the Tafel curve capacitance arc radius of HEACs is much larger than the former in 3.5% NaCl solution, with higher E_corr, lower I_corr, and larger |Z|, R_s, R_f, and R_ct, exhibiting better electro-chemical corrosion performance, which can be attributed to the comprehensive effect of the passivation film as a single FCC solid solution phase.