Understanding Evolution of Metal Microstructures during Dynamic Deformation at Atomic Scales

The response of structural metallic materials under dynamic loading conditions is determined by the evolution of defects, their interaction with each other, and their evolution behavior that dictates the failure behavior. Understanding the different plasticity contributors in FCC, BCC, and HCP metals during various loading and unloading stages using experiments is a challenge due to the fast time scales of the processes at high strain rates. Current experimental capabilities of in situ diffraction provide evidence of dislocation slip, deformation twinning, and phase transformation through real-time characterization of the operating modes in FCC, BCC, and HCP microstructures under shock loading conditions. However, one of the challenges that remain in understanding the relative contributions of the operating deformation modes to the plasticity under such extreme loading environments<b>.</b> This talk will provide an overview of the current understanding of the shock response and identification of plasticity contributors that determine the dynamic (spall) strengths of FCC, BCC, and HCP microstructures as predicted using molecular dynamics (MD) simulations. The talk will highlight our new capabilities to characterize the deformation modes using virtual diffractograms and quantify the corresponding plasticity contributors using virtual texture analysis. Example simulations comprise shock loading and spall failure of FCC, BCC, and HCP microstructures generated using MD simulations. Virtual characterization of microstructures generated at various stages of loading in the simulations reveals the role of loading orientations of grains and misorientation relationships between grains on the nucleation and evolution of phase transformation and twinning variants during shock compression. In addition, the simulations provide new insights into the mechanisms of reverse transformation and detwinning behavior during unloading. The simulations unravel the contributions of the deformation modes on the shifts, broadening, and splitting behavior of the various peaks/spots in the diffractograms for single crystal and polycrystalline Cu, Ta, Fe, and Mg microstructures during shock loading and spall failure.