Inter- and Transgranular Nucleation and Growth of Voids in Shock Loaded Copper Bicrystals

Abstract

Understanding the evolution of dynamic deformation and damage due to spall at grain boundaries (GBs) can provide a basis for connecting micro- to macroscale failure behavior in polycrystalline metals undergoing extreme loading conditions. Bicrystal samples grown from the melt were tested using flyer-plate impacts with shock stresses from 3 to 5 GPa. Pulse duration and crystal orientation along the shock direction were varied for a fixed boundary misorientation to determine thresholds for void nucleation and coalescence in both the bulk and the boundary. Sample characterization was performed using electron backscattering diffraction (EBSD) and scanning electron microscopy (SEM) to gather microstructural information at and around the GB, with emphasis on damage at the boundary. Simulations were performed to interpret experimental results. Initial results show that the kinetics of damage growth at the boundary is strongly affected by pulse duration and stress level and that once a threshold level is reached, damage increases faster at the GB compared to the grain bulks.