Impact response of metastable body-centered cubic high-entropy alloy HfZrTiTa0.53: Deformation and spallation damage

Abstract

The impact responses of the metastable refractory body-centered cubic (BCC) high-entropy alloy (HEA) HfZrTi${\mathrm{Ta}}_{0.53}$ with two different grain sizes ($450\mu m$ or $140\mu m$) are investigated via plate impact experiments. Free surface velocity histories at different peak shock stresses are measured. Both as-received and postmortem samples are characterized with x-ray diffraction, electron back-scatter diffraction, scanning electron microscope and transmission electron microscopy. Multiple deformation mechanisms are identified, including dislocation slip, kink band formation and {332}$〈113〉$ deformation twinning, and the BCC to the hexagonal close-packed (HCP) phase transformation in the BCC matrix, along with dislocation slip and $\left\{10\bar{1}1\right\}〈10\bar{1}2〉$ deformation twinning in the HCP phase. Both the large- and small-grain samples display ductile damage. In contrast with the intergranular voids in the small-grain sample, intragranular voids are predominant in the large-grain sample, leading to its higher spall strength. Quantitative analysis of voids/cracks reveals similar damage characteristics for both grain sizes.