Microstructure Evolution and Wear Mechanism of Si-Effected Al_0.6CoCrFeNi High-Entropy Alloy Coatings by Laser Cladding

Al_0.6CoCrFeNiSix high-entropy alloy coatings were obtained by laser cladding on the surface of 45# steel, and their microstructure evolution and wear mechanism were investigated. The surface morphology, element composition, and phase structure were analyzed, and the results showed that an increase in Si content led to a refinement of the Al_0.6CoCrFeNiSix alloy coatings with a gradual transition from face-centered cubic (FCC) phase to body-centered cubic (BCC/B2) phase in alignment with the equilibrium phase diagram calculated using Pandat thermodynamic calculation software. The dissolution of Si into the solid solution caused lattice distortion which provided the driving force for this phase transition, while segregation of Si, Fe, and Cr facilitated the formation of Al-Ni-rich B2 phase promoting transformation from FCC to BCC phase. Microhardness improved with increasing Si content, reaching 770 Hv_0.2 for the Al_0.6Si_0.4 alloy coating, demonstrating superior performance, while the wear mechanisms differed among the alloys where abrasive wear dominated in the Al_0.6Si_0.0, Al_0.6Si_0.1, and Al_0.6Si_0.2 alloys, whereas oxidation wear was prominent in the Al_0.6Si_0.3 and Al_0.6Si_0.4 alloys. The coating's wear resistance was enhanced due to the formation of a dense oxide film as lubricant resulting from the reaction between Si and oxygen acting leading to significant improvement in the tribological properties.