Effect of microstructural uncertainty on the yield stress of nanocrystalline nickel

Abstract

Numerical simulations can be exploited to understand the sensitivity of the mechanical properties of materials to microstructural variability and hence improve their mechanical performance and reliability. We investigate the effect of the initial microstructure of nanocrystalline (nc) nickel, i.e. grain size, grain size distribution and initial dislocation density, on the yield stress through numerical simulations using a phase field dislocation dynamics model. Our work reveals that the grain size distribution has a significant influence on the yield stress for grain sizes under 32nm and that the initial dislocation density is of key importance in determining the yield stress. Simulations with a zero initial dislocation density exhibit an almost size-independent stress–strain behavior, while Hall–Petch effect was observed in simulations with non-zero initial dislocation density. Using the results of our simulations we construct response surface functions of the yield stress that can be propagated to obtain a probability density function of the yield stress as a function of microstructure variables. We observe that the effect of uncertainty in grain size distribution and initial dislocation density is stronger for smaller grain sizes.