Structure and properties of the CrMnFeCoNi high-entropy alloy irradiated with a pulsed electron beam

Abstract

According to the technology of wire-arc additive manufacturing a nonequiatomic composition CoCrFeMnNi high-entropy alloy (HEA) was obtained. Deformation curves of samples in tension are plotted and analyzed after the HEA fabrication by the methods of wire-arc additive manufacturing (initial state) and after the electron-beam processing (EBP). The EBP results in a decrease in the HEA's strength and plastic properties. Along with a pit character of the fracture a presence of micropores and microlayerings are identified. A study of the HEA's fracture surface after the EBP except for regions with a ductile fracture mechanism revealed regions with a band (lamellar) structure. The area with a band structure increases with a growth in the beam electron density from 25% at 10 J/cm2 to 65% at 30 J/cm2. A diameter of separation pits in fracture bands varies in the limits (0.1–0.2) μm, which is considerably less than those of the remaining part of the HEA sample. An average size of crystallization cells formed in the EBP depends on the energy density of electron beam and increases from 310 nm at 15 J/cm2 to 800 nm at 30 J/cm2. A non-monotonous change in the scalar dislocation density, reaching a maximum value of ∼5.5 · 1010 cm-2 at a distance of 25 μm from the irradiation surface is revealed. It is suggested that defects being formed in surface layers in the EBP may be one of the reasons for decreasing the values of HEA strength and plasticity.