Orientation-dependent dynamic shearing properties and underlying failure mechanisms of laser powder bed fusion of CoCrFeNi high-entropy alloy

Abstract

In order to study the influence of building orientation on the dynamic shearing properties and failure mechanism of laser powder bed fusion (LPBF) of CoCrFeNi high-entropy alloy (HEA) under impacting load, a series of high speed impact tests were systematically conducted on a split Hopkinson pressure bar (SHPB) device at different strain rates. For this purpose, flat hat-shaped samples with a preset shear region were designed. The samples HS0 and HS90 respectively possessed a shear direction parallel and perpendicular to the building orientation. The respective columnar grain orientations of HS0 and HS90 influence the synergistic interaction between dislocation slip and deformation twinning, which is reflected in the differences in mechanical properties. It was observed that HS0 had higher shear yield strength whereas HS90 exhibited better plasticity. Moreover, the two samples show different adiabatic shear sensitivities as adiabatic shear bands (ASBs) were observed when the shear strain reached ∼9.5 and 11.2, respectively. Typical dynamic responses such as adiabatic temperature rise and grain refinement took place in the shear regions. Further, the formation of ultrafine equiaxed grains may be explained using the classical rotational dynamic recrystallization (RDRX) mechanism, which can furnish a sound theoretical basis to understand the deformation behaviors and mechanisms of LPBF CoCrFeNi HEA under impact loads.