Microstructure and Corrosion Resistance of AlCoCrFeNiSix High-Entropy Alloy Coating by Laser Cladding

AlCoCrFeNiSix ( x= 0.1, 0.2, 0.3, 0.4, 0.5) high-entropy alloy coatings were prepared on the surface of AISI 304 stainless steel by laser cladding. The effects of Si element on the microstructure and properties of the high- entropy alloy were investigated by XRD, SEM equipped with EDS, TEM, Vickers hardness tester, and electrochemical workstation. The results show that the high- entropy alloy coatings consist of solid-solution grains with body-centered cubic (bcc) lattice. With the increase of the Si content, the substitutional solid solution of Si element causes the crystal lattice to shrink, and the crystal grains are gradually refined. Besides, the AlNi phase with nano-scale spherical shape is dissolved in the crystal grains, and a small amount of Cr23C6 carbides are precipitated along the grain boundaries. The evolution of the microstructure leads to an increase in the microhardness of the coating, and the maximum hardness ( HV0.3) reaches 8481 MPa. The thermodynamic corrosion tendency and uniform corrosion rate of AlCoCrFeNiSix high-entropy alloy coating are lower than those of the AISI 304 stainless steel. The doping of Si element improves the repair ability and stability of the passivation film, and promotes the corrosion mechanism to transform from pitting corrosion developed by autocatalysis to intergranular corrosion.