Mechanical behavior and microstructure of Ti20Hf20Zr20Ta20Nb20 high-entropy alloy loaded under quasi-static and dynamic compression conditions

Abstract

The microstructure and the mechanical behavior of equimolar Ti20Hf20Zr20Ta20Nb20 high-entropy alloy in a wide range of initial strain rates between ∼ 10- 3 s- 1 and ~ 3.4 × 103 s- 1 were studied. A significant increment in the yield strength with increasing strain rate was observed. The yield strength at ~ 3.4 × 103 s- 1 was about 40% higher than that measured at ~ 10- 3 s- 1. Analysis by electron backscatter diffraction shows that in the low strain rate regime (up to ~ 10 s- 1) the deformation occurs mainly in evenly distributed bands, while in the dynamic regime the deformation is strongly localized in macroscopic shear bands accompanied by softening even after the onset of yielding. The Kernel Average Misorientation technique reveals a high level of lattice rotation within these bands that also carries intense shear. In addition, X-ray diffraction line profile analysis indicates that the sharp increase in the flow stress is mostly related to an increase of the dislocation density.