Tensile Failure Modes in Nanograined Metals with Nanotwinned Regions

Nanotwinned (NT) regions can compensate the lower ductility of nanograined (NG) matrix so that NG metals with NT regions can achieve high strength and modest ductility. Main factors affecting the strength and ductility of the NG metals with NT regions have not been systematically and numerically investigated. Based on the strain gradient plasticity and Johnson–Cook failure criterion, computer simulations are carried out to clarify the effects of twin spacing together with shape and distribution of NT regions on their strength and ductility. Our calculations indicate that these attributes have significant effects on the overall ductility. In particular, it is discovered that a critical twin spacing marks the reversal of the overall ductility, that is, the overall ductility decreases and then increases with the continuous increase of twin spacing. Compared with the circular NT regions, the square and oblique square ones are found to provide higher overall strength and ductility. For the circular and oblique square NT regions, array arrangement tends to perform better in strengthening and toughening, while for the square NT regions, staggered arrangement is advisable. We have also uncovered three distinct failure modes, including fracture of matrix, fracture of NT regions, and interface debonding. Furthermore, fracture of NT regions can enhance the overall ductility and lead to the reversal of the overall ductility. It is believed that this study has provided significant insights into the roles of twin spacing together with shape and distribution of NT regions on the overall strength and ductility of this novel class of metals.