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

The impact responses of the metastable refractory body-centered cubic (BCC) high-entropy alloy (HEA) HfZrTiTa0.53 with two different grain sizes (450μm or 140μm) 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 {101̄1}〈101̄2〉 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.