In situ study on plastic deformation mechanism of Al0.3CoCrFeNi high-entropy alloys with different microstructures

Al 0.3 CoCrFeNi high-entropy alloys (HEAs) have attracted the attention of researchers owing to their excellent mechanical properties. In this study, Al 0.3 CoCrFeNi HEAs with typical grain microstructures were fabricated and subjected to tensile tests, along with in situ scanning electron microscopy–electron backscatter deformation (SEM–EBSD), to determine the relationship between the grain microstructure, plastic deformation, and mechanical properties. The in situ EBSD analysis showed that the HEA sample with fine grains (FGs) exhibited more significant grain boundary deformation than that with coarse grains (CGs). The FG sample had a more uniform dislocation density distribution than the CG sample, and no noticeable excessive dislocation density was observed inside the grain. This indicates that the plastic deformation of the FG sample could be distributed more homogeneously without a prominent local stress concentration. Based on the grain structures from EBSD scans, crystal plasticity finite element modeling (CPFEM) and analysis were conducted to analyze the grain-level stress and strain heterogeneities. The results showed that during the tensile process, high stress was initially distributed near the B2 phase and subsequently at the grain boundaries of the HEA with increase in tensile deformation. The local stress distribution in the matrix was significantly affected by the B2 phase. Although high stress was distributed near the B2 phase during plastic deformation, the probability of crack initiation at the phase boundaries was low. This can be partly attributed to the formation of deformation twins at the junction of the B2 phase and FCC matrix, which releases the stress. • The strength of Al 0.3 CoCrFeNi HEA is significantly increased by the fine grain strengthening and second phase strengthening. • CPFEM results show that B2 phase plays a dominant role in the improvement of HEA strength. • The release of local stress by deformation twins inhibits the initiation of cracks at the phase boundary. • The inhomogeneous deformation in the grain of CG (coarse grain) samples leads to crack initiation. • In tensile deformation, the high stress field gradually extend from the phase boundary to the grain boundary.