metallic glass at heating rates spanning over six orders of magnitude

The glass transition and primary crystallization of melt-spun Al₈₆Ni₆Y_4.5Co₂La_1.5 metallic glass have been investigated at continuous heating covering more than six orders of magnitude of heating rates (0.083 K/s to 40,000 K/s). Differential fast scanning calorimetry (DFSC) and conventional differential scanning calorimetry (DSC) were employed, by which the glass transition kinetics was analyzed. In particular, it is shown that the heating rate dependence of the glass transition temperature can be described by a generalization of the Bartenev-Ritland equation utilizing the Vogel-Fulcher-Tammann equation for the description of the viscosity and the Maxwellian relaxation time. This result is confirmed by measurements of primary crystallization performed also over a wide range of scanning rates. The results reveal that the kinetics of crystallization follows a non-Arrhenius behavior. In the analysis a theoretical model is employed which takes into account the effect of decoupling of viscosity and diffusion, i.e., the breakdown of the Stokes-Einstein equation. In this way, a modified description of the crystal growth kinetics in the whole temperature range is obtained.