Prediction of the glass forming ability in Cu-Zr binary and Cu-Zr-Ti ternary alloys

By combining CALPHAD technique with kinetic approach, we evaluated the glass forming ability(GFA) of nine compositions of Cu-Zr and thirteen of Cu-Zr-Ti alloys in terms of critical cooling rate and fragility. The driving forces for crystallization from the undercooled liquid alloys were calculated by using Turnbull and Thompson-Spaepen (TS) Gibbs free energy approximate equations, respectively. Time-temperature-transformation (TTT) curves of these alloys were obtained with Davies-Uhlmann kinetic equations based on classical nucleation theory. With Turnbull and TS equations, the critical cooling rates are calculated to be in the range of 9.78 × 103-8.23 × 105 K/s and 4.32 × 102-3.63 × 104 K/s, respectively, for Cu-Zr alloys, and 1.38 × 102-7.34 × 105 K/s and 0.64-1.36 × 104 K/s, respectively, for Cu-Zr-Ti alloys. The calculated fragility parameters are in the range of 6.32-9.3 for Cu-Zr binary and 5.7-8.24 ternary alloys, respectively. The comparison of the calculated results to the experimental data indicates that the cooling rate obtained with TS equation is more valid than that with Turnbull equation, and that obtained by other researchers for the evaluation of GFA. The fragility be used as parameter to evaluate relatively the GFA in an alloy system. This work suggests that the combined thermodynamic and kinetic modeling may provide an effective method for the prediction of GFA in Cu-Zr and Cu-Zr-Ti alloys.