Mechanical properties and microstructure of the Al0.3CoCrFeNiTi0.3 high entropy alloy under dynamic compression

Abstract

In this work, the mechanical properties and corresponding microstructural evolution of the as-cast Al0.3CoCrFeNiTi0.3 high-entropy alloy (HEA) under quasi-static and dynamic compressive loadings were investigated. The HEA consisted of FCC/L12 + BCC/B2 mixed solutions exhibited a good combination of high strength and large ductility upon quasi-static loading, which is mainly due to the strengthening effect of coherent L12-nanoparticles. The HEA exhibited a significant positive strain rate effect, and its yield strength rised from 810 to 1181 MPa when the strain rate increased from 10−3 to 4700 s−1. Compared with the quasi-static condition, the density of stacking fault (SF) networks and immobile Lomer–Cottrell (L-C) locks were greater under dynamic loading. Furthermore, the deformation mode of the HEA was dominated by planar glide under high strain rate loading, and the dislocation substructure showed Taylor lattice, high-density dislocation walls and intersected microbands with the increase of strain. The dynamic Hall–Petch and microband-induced plasticity effects could be responsible for the excellent dynamic compressive properties. Fractographic observations indicated that the fracture of the HEA is controlled by the mixed ductile-brittle mechanism under dynamic compressive loading. An improved Johnson-Cook (J-C) constitutive model considering adiabatic temperature rise was employed to predict the plastic flow behavior of the HEA under dynamic conditions and the improved J-C model was in good agreement with the experimental results.