Microstructural evolution in void coalescence induced by plate-impact loading in ultrapure aluminum

Under dynamic tensile loading, Spallation damage results from the nucleation, growth and coalescence of voids in a ductile metal. Microvoid nucleation is the major damage process of damage evolution. The microstructures of microvoid, which result from dynamic tensile loading in high pure aluminum 99.999{\%}, were characterized by a transmission electron microscope (TEM) and a high-resolution TEM. It was found that there may be a new nucleation mechanism of damage evolution in a ductile metal, which might be called melt nucleation. During shock compression, shock energy gives rise to local melting in high pure aluminum, and then a new free surface is generated under the tensile stress in the melting areas. Nanocrystalline amorphous metal is produced by rapid quenching a molten aluminum. In our experimental observations, the grain size of Nanocrystalline amorphous aluminum is 5-20 nm. This will increase understanding of the physical processes of dynamic tensile fracture of materials under high strain rate deformation.