Sub-Tg annealing effect on the kinetics of glass transition and crystallization for a Ti-Zr-Be-Fe bulk metallic glass

The influence of sub-T-g pre-annealing on the kinetics of glass transition and crystallization of a lightweight Ti41Zr25Be28Fe6 bulk metallic glass (BMG) has been investigated by isochronal and isothermal differential scanning calorimetry tests. It was found that sub-T-g annealing obviously enlarges the supercooled liquid region of Ti41Zr25Be28Fe6 BMG, indicating an enhanced thermal stability. The activation energies for glass transition and crystallization of the as-cast and pre-annealed samples have been calculated and compared. The pre-annealed samples possess smaller values of fragility parameter and longer incubation times upon isothermal heating compared with the as-cast sample, indicating a retarded crystallization process. The isothermal crystallization kinetics of the samples with different annealed states has been investigated in terms of the Johnson-Mehl-Avrami equation and local Avrami exponent. The current study reveals a clear sub-T-g annealing effect on the kinetics of glass transition and crystallization of Ti41Zr25Be28Fe6 glassy alloy and the possible mechanisms have also been proposed.