Kinetics of crystallization process for bulk glass forming Zr-base alloys

Abstract

The crystallization kinetics of Zr 65Ni 10Cu 17.5Al 7.5 (alloy I) and Zr 52.5Ni 14.6Cu 17.9Al 10Ti 5 (alloy II) are investigated. Two-stage crystallization takes place during continuous heating of the glassy alloy I, resulting in the transformation of the glass to the metastable α-Zr-solid solution and Zr-base quasicrystals with an activation energy of 309 KJ/mol in the first-stage and the formation of Zr 2Cu compound and the stable α-Zr-solid solution with an activation energy of 227 KJ/mol in the second-stage. For alloy II, one-stage crystallization with an activation energy of 333 KJ/mol occurs during continuous heating of the glass, resulting in the formation of Zr 3Al and α-(Zr,Ti)-solid solution. Based on the DSC data and calculations, both the alloys go through with three stages of crystallization mechanism during isothermal annealing, i.e. (1) surface nucleation and growth, (2) three-dimensional nucleation and growth, and (3) crystal growth. The TEM observation on Zr 52.5Ni 14.6Cu 17.9Al 10Ti 5 alloy is in good agreement with the calculations.