Universal percolation threshold for ductile-brittle transition of amorphous alloys

Based on the free volume, shear transformation zone and percolation theory, a new percolation model has been established to investigate the ductile-brittle transition in amorphous alloys. Taking the binary Cu25Zr75 amorphous alloy for example, the influence of the free volume concentration and flow unit dispersity on its percolation threshold value was analyzed. The results show that the concentration of flow units reach a critical value when the ductile-brittle transition occurs in the Cu25Zr75 amorphous alloy, and this critical value is independent of the concentration of the free volume but dependent on the dispersity of flow units. Furthermore, the percolation threshold values of La-, Zr-, Cu-, Pd-, Fe-, Sr- and Tm-based amorphous alloys were also calculated, a percolation threshold value of ~0.516 for ductile-brittle transition in these amorphous alloys was obtained. Therefore, our analysis results suggest that ~0.516 appears to be a universal percolation threshold value for ductile-brittle transition in amorphous alloys.