Effects of grain size distribution on the mechanical response of nanocrystalline metals: Part II

The model of Zhu et al. [Zhu B, Asaro RJ, Krysl P, Bailey R. Transition of deformation mechanisms and its connection to grain size distribution in nanocrystalline metals. Acta Mater 2005;53(18):4825–38] is further developed and used to explore the effect of grain size and grain size distribution, along with the influence of material parameters, on the mechanical response of nanocrystalline face-centered cubic aggregates. This model accounts for the simultaneous contributions of deformation mechanisms including grain boundary emission of dislocations and/or stacking faults, as well as for mechanisms such as grain boundary sliding and for natural transitions between the relative dominance of each. The effect of grain growth during deformation is also quantitatively assessed via simulation of recently obtained data on indentation tests in which dynamic grain growth was documented through the measurement of changes in grain size distribution and concomitant changes in hardness. The simulations provide a plausible description of the observed phenomenology and further underscore the unstable nature of nanocrystalline grain size distributions. The possibility of incorporating additional potential deformation mechanisms such as Coble creep, as has been proposed in other models, is discussed and shown to be straightforward addition to the model. Recently obtained data on texture development is analyzed via texture predictions for aggregates subject to finite deformations via high pressure torsion (HPT). The phenomenology is assessed specifically with regard to the potential use of texture measurements for confirming the importance of crystallographic mechanisms vs. those such as grain boundary sliding.