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

Multicomponent chemical short range order (MCSRO) undercooling principle wa s proposed as a criterion to evaluate the glass forming ability (GFA) of al loys. The thermodynamic model of MCSRO was established in order to calculat e the MCSRO undercooling. Comprehensive numerical calculations using MCSRO software were conducted to obtain the composition dependence of the MCSRO u ndercooling in Zr-Ni-Cu, Zr-Si-Cu, and Pd-Si-Cu ternary systems. By the MCS RO undercooling criterion, the composition ranges with great GFA in these t ernary systems were predicated. It is shown that the prediction by MCSRO un dercooling principle is in general consistent with the well-known empirical rules proposed by Inoue. According to the MCSRO undercooling principle, th e 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 a lso illustrates that Pd-based alloys which easily form a metallic glass exh ibit an extraordinary deep MCSRO undercooling. By calculating TTT curves in Zr-Ni-Cu system, it is shown that the average critical cooling rates are e stimated to be as low as similar to 100 K/s for the alloy with deep MCSRO u ndercooling. 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 undercoo ling principle.