Scale dependence of the strain rate sensitivity of Twinning-Induced Plasticity steel

We report that the mechanical behavior of Twinning-Induced Plasticity steel deformed at different strain rates depends on the scale of observation. Slower-deformed samples have a higher twin density, which leads to larger flow stress measured in a macroscopic uniaxial test. When probed at the nanoscale by nano-indentation, samples pre-deformed at smaller strain rates exhibit systematically smaller hardness than samples pre-deformed at higher rates. The hardness-based nanoscale strain rate sensitivity is positive. The strain rate sensitivity measured by micro-hardness shifts to negative values as the indenter size and the probed volume increase. The effect is linked to the dislocation-twin interaction mechanism. (C) 2016 Elsevier B.V. All rights reserved.