Microstructure evolution and properties of Fe-Ni-Cr-Co-Mo-W high-entropy alloy coatings by plasma surface alloying technology

The purpose of this study is to develop a new type of high-entropy alloy (HEA) coating with high temperature oxidation resistance. In this paper, the Fe-Ni-Cr-Co-Mo-W HEA coatings were prepared by plasma surface alloying technology with different holding temperatures (1150 °C, 1200 °C, 1250 °C, 1300 °C). The microstructure morphology evolution and properties of Fe-Ni-Cr-Co-Mo-W HEA coatings were systematically studied. The results indicate that all the Fe-Ni-Cr-Co-Mo-W HEA coatings are composed of a deposition layer and diffusion layer, forming gradient structure HEA coating. The element gradient distribution in the diffusion layer achieves the metallurgical bonding effect. The deposition layer conforms to the definition of HEAs based on the composition or configuration entropy, and forms the surface HEAs. The phase of Fe-Ni-Cr-Co-Mo-W HEA coatings is all composed of HCP phase + FCC phase. The higher the holding temperature, the greater the supply of alloying elements are deposited by sputtering, and the higher the density of surface vacancy formation, which promotes the diffusion of atoms and the growth of grain structure. The surface morphology of the Fe-Ni-Cr-Co-Mo-W HEA coating changes from the pinecone-like large particle dense accumulation morphology to flat and compact plane, and then to fine particles compact accumulation morphology. The properties of the 1300 °C Fe-Ni-Cr-Co-Mo-W HEA coating is the best, the abrasive resistance and high temperature oxidation resistance are 3.66 and 5.5 times higher than those of the matrix respectively. The results indicate that the Fe-Ni-Cr-Co-Mo-W HEA coating with gradient structure and metallurgical bonding has a good application prospect.