Crystallisation kinetics of Zr41.2Ti13.8Cu12.5Ni10Be22.5 BMG alloy during heating

Abstract

The crystallisation behaviour of Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass (BMG) alloy during heating from the amorphous state has been investigated. Upon heating, the nucleation process was not consistent with classical nucleation theory. This problem can be overcome by substituting the nucleation density with the number density of nuclei, N, for growth of the crystalline phase, which is estimated from the length scale of the microstructure. The growth of crystalline phase is the governing process for crystallisation of the Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy upon heating. The growth process is more important than the nucleation process for analysing the crystallisation mechanisms of the amorphous state. Non-isothermal heating DSC data have been analysed with a modified crystallisation kinetics model based on the non-isothermal transformation theory. Using this model, the onset crystallisation temperatures at various heating rates have been calculated. The calculated critical heating rate to avoid crystallisation is 190 K s−1, which matches well with the experimental value. The onset crystallisation times for isothermal annealing conditions have also been calculated and compared with the isothermal DSC data. Time temperature transformation (TTT) and continuous heating transformation (CHT) diagrams have been constructed quantitatively. The crystallisation kinetics of BMG alloys can be more reliably analysed with our modified crystallisation kinetics model than with several nucleation models.