Critical Strengths for Slip Events in Nanocrystalline Metals: Predictions of Quantized Crystal Plasticity Simulations

This article studies how the monotonic and cyclic stress-strain response of nanocrystalline (NC) metals is affected by the grain-to-grain distribution of critical strengths (τc) for slip events, as well as plastic predeformation (εprep). This is accomplished via finite element simulations that capture large jumps in plastic strain from dislocation slip events—a process referred to as quantized crystal plasticity (QCP).[1] The QCP simulations show that τc and εprep significantly alter the monotonic and cyclic response at small strain, but only τc affects the response at large strain. These features are exploited to systematically infer the τc and εprep characteristics that best fit experimental data for electrodeposited (ED) NC Ni. Key outcomes are the following: (1) the τc distribution is truncated, with an abrupt onset of slip events at a critical stress; (2) εprep = −0.4 pct, signifying precompression; (3) there is reverse slip bias, meaning that reverse slip events are easier than forward events; and (4) highly inhomogeneous residual stress states can be enhanced or reduced by tensile deformation, depending on εprep.