Tuning the strength-ductility synergy of nanograined Cu through nanotwin volume fraction

Nanograined (NG) metals with nanotwinned (NT) regions can overcome the inferior ductility of NG metals and achieve high strength and modest ductility. Based on the strain gradient plasticity and Johnson–Cook failure criterion, we simulate the dependences of their strength and ductility on volume fraction, twin spacing, as well as shape and distribution of NT regions in NG Cu. It is found that these factors have significant impact on the overall ductility. In particular, the overall ductility abnormally decreases with the increase in the volume fraction of NT regions, which is directly related to the failure modes of this material system. Interface debonding can explain the above abnormal decrease in overall ductility. In addition, with the increase in twin spacing, fracture of NT regions can cause different reversals of overall ductility. We also found that, when the NT regions are of the oblique square type, the overall ductility is significantly lower than when they are of the circular and square types. In most cases, the array arrangement of NT regions is superior to the staggered arrangement for the improvement of the overall ductility. It is believed that these reported results can contribute to a deeper understanding of this novel material system.