2005 Volume 46 Issue 12 Pages 2931-2939
The glass-forming ability of Zr–Ti–Be ternary alloys has been evaluated by coupling the Davies–Uhlmann kinetic formulations with the CALPHAD approach. In the computations, time-temperature-transformation (TTT) curves were obtained, which are a measure of the time necessary for the formation of detectable amounts of a crystalline phase from a supercooled liquid as a function of temperature. The critical cooling rates were calculated from the TTT curves, and these enabled us to evaluate the glass-forming ability of this ternary alloy. The driving force for the crystallization of the crystalline phases was derived from the Gibbs energy functions of each phase, where thermodynamic calculations were carried out using a simple ternary extrapolation of the binary data sets with no solubility of the third element in the binary phases except for the liquid, hcp, and bcc phases. The evaluated glass-forming compositional range was in good agreement with experimental data from the Be-rich side. However, the calculated critical cooling rates for some alloys were too low. The validity of the ideal mixing of the metastable ZrBe(B2) and TiBe(B2) phases, and the possibility of the formation of the ternary B2 phase are also discussed from an ab initio energetic point of view, and the critical cooling rates were recalculated assuming an ideal mixing of the metastable ZrBe(B2) and TiBe(B2) phases. The results show that the magnitude of the calculated values achieved was reasonable.
