Strengthening mechanisms in nanoporous metallic glasses

It has been shown that metallic glasses (MGs) can have enhanced ductility by properly introduced pores. However, the pore effects on the yield strength and the underlying mechanisms have yet to be fully clarified. In this paper, nanoporous MGs with regularly distributed elliptical pores are investigated by large scale molecular dynamics simulations. Obtained results show that, when increasing the semi-axis a in the loading direction and fixing the other semi-axis b of the pores, the strength of the nanoporous MGs increase firstly to reach a maximum value and then decreases. It is found that the porosity and pore shape are the main factors affecting the strength. For a given porosity, the yield strength increases first and then approaches an asymptotic value with increasing a. The underlying mechanism is that the shear bands transit from localization to spreading. For a given pore shape, the yield stress decrease with increasing a. And this is because the increase of porosity leads to reduction in strength. Due to the above mechanisms, there exists a maximum strength at a critical size where the shear band evolution transition occurs. A model for the critical size of a(cri) is proposed to predict the maximum strength.