STRUCTURAL-PHASE STATES AND PROPERTIES OF HIGH-ENTROPY CrMnFeCoNi ALLOY AFTER ELECTRON BEAM TREATMENT

For CoCrFeMnNi high-entropy alloy (HEA) of non-equiatomic composition, obtained by means of wire-arc additive manufacturing (WAAM), tensile strain curves of the samples after manufacturing and after electron beam processing (EBP) have been recorded and analyzed. Dependences of tensile strength and elongation, microhardness on electron beam energy density have been established. It has been found that decrease in ultimate strength and relative elongation increases with an increase in electron beam energy density. The dimple rapture and presence of micropores and microstratifications are revealed. Regions with a stripe (plate) structure are shown, the area of which increases with an increase in electron beam density from 25% at 10 J/cm² to 65% at 30 J/cm². With an increase in electron beam energy density, thickness of molten layer changes within (0.8 – 5.0) μm, and the average size of crystallization cells increases from 310 nm at 15 J/cm² to 800 nm at 30 J/cm². Nonmonotonic change in scalar density of dislocations has been established, reaching the maximum value (of ~5.5∙1010 cm^-2) at a distance of 25 µm from the irradiation surface. It is shown that non-misoriented cellular dislocation substructure with cell sizes from 400 nm to 600 nm is formed in the surface layer. Moving away from the surface, dislocation substructure changes from cellular to cellular-reticular and, at distance of 120 – 130 μm, to the original alloy substructure with chaotic distribution of dislocations. It has been suggested that the defects formed in the surface layers during EBT may be one of the reasons for decreasing extreme values of strength and ductility of HEA.

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