Prediction of mechanical properties in bimodal nanotwinned metals with a composite structure

Nanostructured face-centered cubic (fcc) metals with nanoscale twin lamellae and multiple distribution of microstructural size are proved to possess higher yield strength and good ductility. In this paper, a mechanism-based theoretical model is developed to simulate the yield strength, strain hardening, and uniform elongation of the nanotwinned composite metals with bimodal distribution of microstructural size. The mechanisms of strengthening and the failure in such bimodal nanotwinned metals are studied for evaluating the strength and ductility. A modified mean-field approach is adopted here to calculate the total stress-strain response of this kind of nanotwinned composite structures. The contribution of microcracks generated during plastic deformation has been taken into account to predict strain hardening and uniform elongation. Our simulation results indicate that the proposed model can successfully describe the mechanical properties of bimodal nanotwinned metals with a composite structure, including the yield strength and ductility. We further demonstrate that the yield strength and elongation are both sensitive to the twin spacing and the volume fraction of components. The calculations based on the proposed model agree well with the experimental results. These findings suggest that the high yield strength and high ductility can be achieved by optimizing the grain size and the twin spacings in the nanotwinned composite structures.