Intragranular void formation in shock-spalled tantalum: Mechanisms and governing factors

Intragranular void formation in polycrystalline tantalum is investigated with plate impact experiments and molecular dynamics simulations, as regards its mechanisms and governing factors: grain boundary (GB) misorientation, grain orientation, grain size and shock pressure. Free-surface velocity history measurements are performed to obtain spall strength. Electron backscatter diffraction characterizations are used to obtain spatial distribution of voids, GB misorientation, and grain orientation associated with twins and intragranular voids. Intragranular voids are smaller in size but larger in number than inter granular voids, and nucleate in the GB vicinities. Smaller grains are favorable for the formation of intergranular and intragranular voids. At higher shock pressure, intragranular voids increase in fraction and tend to distribute at grain centers. Deformation twinning depends on grain orientation and prefers to form at high-angle GBs. However, intragranular voids have negligible dependence on grain orientation and favor medium-angle GBs, and the preference is enhanced slightly with increasing impact velocity and decreasing grain size. The simulations show GB-induced multiple-slip, slip-slip intersections and strain localizations act as the prerequisites to intragranular void formation. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.