Tensile fracture behaviors of a laser powder deposited Fe–30Mn–10Cr–10Co–3Ni high-entropy alloy: In situ x-ray computed microtomography study

Abstract

The defect evolution and fracture mechanism of a laser powder deposited Fe–30Mn–10Cr–10Co–3Ni alloy in the course of uniaxial tensile tests was investigated by in-situ high-resolution computed microtomography (CT) and electron back-scattered diffraction (EBSD). The influences of surface wrinkling and the long and straight grain boundary on the defect evolution and fracture mechanism were discussed emphatically. The results showed that pores were not the source of crack initiation. During plastic deformation, the pore volume did not change significantly, but the pore shape varied. The development of voids was observed only in the zones with strain localization. However, the plastic damage voids were not the source of fracture cracks, neither growing nor aggregating into macroscopic cracks. The cracks in the specimens were initiated at the long and straight grain boundary with an angle of about 45° relative to the applied load and the Taylor factors on both sides of the grain boundary differed greatly. Severe plastic damage occurred at the surface and near-surface of the tensile specimens as a result of surface wrinkling. The void volume fraction of a superficial zone was several times higher than that in the bulk of the specimens, and there were many cracks with an angle of about 45°relative to the applied load. The tensile fracture behaviors of the laser powder deposited Fe–30Mn–10Cr–10Co–3Ni alloy were different from the microvoid coalescence fractures of traditional polycrystalline ductile alloys, and the fracture in the former ones was caused by the propagation of surface and near-surface cracks. Fractures had neither shear lips nor radial zones. The fundamental understanding will provide a theoretical basis for future fabrication and post treatment to enhance the mechanical properties of similar alloys.