Grain size dependent microstructure and texture evolution during dynamic deformation of nanocrystalline face-centered cubic materials

Abstract

Evolution of microstructure and texture in nanocrystalline (nc) face-centered cubic materials subjected to high-strain-rate compression are investigated. Three nc materials, differing in grain size or stacking fault energy, namely, 27 nm Ni, 70 nm Ni, and a 27 nm NiCo alloy are deformed under high strain rates (8000–23000 s−1) using the split-Hopkinson pressure bar technique. The transmission Kikuchi diffraction technique and discrete-crystal plasticity finite element (D-CPFE) simulations are used to evaluate structural evolution. Experimental results show that grain growth and grain refinement occurred in samples with small and large initial grain sizes, respectively, while all deformed materials evolve to a (110) texture. The D-CPFE simulations, built for grain-size dependent nc deformation with no fitting parameters, reveal that partial dislocation slip caused faster texture evolution than full dislocation slip. Comparison between experimental and simulation results suggests that the (110) texture is mainly generated by combined full and partial dislocation slip in the 27 nm and 70 nm Ni samples, and by partial dislocation slip alone in the NiCo alloy. Deformation twinning made almost no contributions to the observed texture evolution. Grain-boundary-mediated deformation facilitates grain coarsening, while partial dislocation activities help to promote dynamic stabilization and further refinement of the nano-grains. The highly coupled evolution of microstructure and texture during dynamic deformation is controlled by a synergy of grain size and strain rate effects.