In order to improve the hardness and wear resistance of TC4 alloy under extreme service conditions in aerospace, FeCoNiCrAl high-entropy alloy(HEA) coatings are prepared on the surface of TC4 alloy using direct laser deposition technology. The result shows that the direct laser deposited FeCoNiCrAl HEA coating formed a good metallurgical bond with the TC4 alloy substrate, and the FeCoNiCrAl HEA is deposited in a single-phase body-centred cubic daisy-like equiaxed grains structure with an average grain size of 8.49 μm, and the grains were randomly distributed in (001), (101) and (111) and without obvious preferential growth direction. Elemental segregation was observed in the coating, with Al, Co and Ni elements segregating into the daisy-like equiaxed grains and Fe and Cr elements segregating between the dendrites, while Co, Cr and Ni elements are find to diffuse into the transition region(TR). The average microhardness of the direct laser-deposited FeCoNiCrAl HEA coating is 611.8 HV0.5, which is 1.6 times of that in TC4 alloy (374.9 HV0.5), and the average microhardness of the TR is 699.1 HV0.5 due to the significantly finer dendritic structure and the solid solution strengthening effect of Co, Cr and Ni elements, which is approximately 1.8 times that of the TC4 alloy substrate
Ti6Al4V/Inconel 718 functionally graded material combines the advantages of the two materials, it can fully meet the requirements of high temperature resistance, high strength and light weight in the extremely harsh environment of aerospace. Ti6Al4V/ Inconel 718 functional gradient materials were prepared by directed laser deposition. Scanning electron microscopy and electron probe micro-analysis were used to observe the microstructure and element distribution of functional gradient samples. The mechanical properties of the functionally graded sample were measured by Vickers hardness tester. The results show that the interface between Ti6Al4V and Inconel 718 is cleavage fracture, and the cleavage fracture is related to the formation and concentration of Ti2Ni, NiTi and Ni3Ti intermetallic compounds. A well-formed gradient sample is prepared by using gradient transition. Through the effective gradient transition form(100%Ti6Al4V- 90%Ti6Al4V/10% Inconel 718-80% Ti6Al4V/20% Inconel 718-100% Inconel 718), the element inhomogeneity at the interface is alleviated and a good metallurgical bond is formed. Along the gradient direction, the microhardness gradually increases with the increase of Inconel 718, reaching the maximum of 811HV. The reason for the increase in hardness is related to solid solution and precipitation strengthening of Ti2Ni intermetallic compounds.
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