Multicomponent chemical short range order undercooling and the formation of bulk metallic glasses

Multicomponent chemical short range order (MCSRO) undercooling principle was proposed as a criterion to evaluate the glass forming ability (GFA) of alloys. The thermodynamic model of MCSRO was established in order to calculate the MCSRO undercooling. Comprehensive numerical calculations using MCSRO software were conducted to obtain the composition dependence of the MCSRO undercooling in Zr-Ni-Cu, Zr-Si-Cu, and Pd-Si-Cu ternary systems. By the MCSRO undercooling criterion, the composition ranges with great GFA in these ternary systems were predicated. It is shown that the prediction by MCSRO undercooling principle is in general consistent with the well-known empirical rules proposed by Inoue. According to the MCSRO undercooling principle, the composition with great GFA in the range of Zr-Ni-Cu system is Zr=62.5-75, Cu=5-20 and Ni=12.5-25, (Ni/Cu=1-5), which is in agreement with the recent experimental results of the quaternary Zr-Ni-Cu-Ti alloy The calculation also illustrates that Pd-based alloys which easily form a metallic glass exhibit an extraordinary deep MCSRO undercooling. By calculating TTT curves in Zr-Ni-Cu system, it is shown that the average critical cooling rates are estimated to be as low as similar to 100 K/s for the alloy with deep MCSRO undercooling. As an example of an effective bulk metallic glass (BMG) design method, a new kind of Zr-Si-Cu BMG is explored based on the MCSRO undercooling principle.