Dislocation motion transitions from thermally activated to continuous glide when deformation rate increases. The ballistic transport of dislocation leads to significant dislocation-phonon interactions that result in material embrittlement, contributing to material failure under impact. Understanding dislocation-phonon drag is critical for designing materials for extreme conditions but remains largely qualitative due to the difficulty of characterizing material behaviors at ultra-high rates. Using a small-scale impression-based approach combining laser-induced microprojectile impact and spherical nanoindentation, we systematically characterized material behavior over a wide range of strain rates (1 s-1 to 109 s-1). The similar deformation length scales and geometries, but distinct mechanistic differences in microprojectile impact and spherical nanoindentation, enabled the development of a theoretical framework that fully deconvolutes and quantifies dislocation drag contributions during ultra-high strain rate impacts. We show that the dislocation drag regime can be suppressed in nanocrystalline alloys at strain rates up to 109 s-1.
(Corresponding author: Mostafa Hassani hassani@cornell.edu)
