Theoretical prediction for mechanical properties in nanotwinned and hierarchically nanotwinned metals with different twin orders

Abstract

The mechanism-based plasticity model on the mechanical properties in nanotwinned and hierarchically nanotwinned metals is further developed, in which the analytical formulae of flow stress and failure strain with respect to various factors are provided. The strength, ductility and fracture toughness in metals with different twin orders are analyzed systemically based on the theoretical model, and the effects of grain size and twin spacing are emphasized. It shows that the effect of twin spacing is significant, and high strength combined with good ductility can be achieved by optimizing the combination of twin spacing in different layers of twin lamellae. Regarding to metals with different twin orders, the variation of mechanical properties with the twin spacing is different, and relatively good mechanical performance can also be achieved in materials with low twin order by adjusting the twin spacing, and it could even be better than that in metals with higher twin orders. Besides, grain size also contributes to the mechanical properties, there may be a critical grain size at which the ductility in the hierarchically nanotwinned metal reaches the peak value, and the relationship between the mechanical property and the twin spacing would change in the case of extremely small grain size. Related analysis is of great importance for the material design in which the optimization of mechanical properties is achieved and the manufacture difficulty can be reduced.