Independence of Slip Velocities on Applied Stress in Small Crystals

Directly tracing the spatiotemporal dynamics of intermittent plasticity at the micro‐ and nanoscale reveals that the obtained slip dynamics are independent of applied stress over a range of up to ∼400 MPa, as well as being independent of plastic strain. Whilst this insensitivity to applied stress is unexpected for dislocation plasticity, the stress integrated statistical properties of both the slip size magnitude and the slip velocity follow known theoretical predictions for dislocation plasticity. Based on these findings, a link between the crystallographic slip velocities and an underlying dislocation avalanche velocity is proposed. Supporting dislocation dynamics simulations exhibit a similar regime during microplastic flow, where the mean dislocation velocity is insensitive to the applied stress. Combining both experimental and modeling observations, the results are discussed in a framework that firmly places the plasticity of nano‐ and micropillars in the microplastic regime of bulk crystals. The spatiotemporal properties of intermittent slip (dislocation avalanches) in nano‐ and microcrystals is traced during deformation. The velocities of the dislocation avalanches are found to be insensitive to both stress and strain. This unexpected behavior is modeled with dislocation dynamics simulations, and it is proposed that the plasticity in the explored size range from 300 to 5000 nm is dynamically equivalent to microplasticity in bulk crystals.