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 (τ _c ) for slip events, as well as plastic predeformation (ε _pre ^p ). 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 τ _c and ε _pre ^p significantly alter the monotonic and cyclic response at small strain, but only τ _c affects the response at large strain. These features are exploited to systematically infer the τ _c and ε _pre ^p characteristics that best fit experimental data for electrodeposited (ED) NC Ni. Key outcomes are the following: (1) the τ _c distribution is truncated, with an abrupt onset of slip events at a critical stress; (2) ε _pre ^p  = −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 ε _pre ^p .