In-situ probing of metallic glass formation and crystallization upon heating and cooling via fast differential scanning calorimetry

The crystallization of small-scale Au-based metallic glass samples was investigated by fast differential scanning calorimetry. Rapid cooling and heating makes possible in-situ probing of glass formation from the supercooled liquid state or direct transition from the glassy state to the equilibrium liquid and, thereby, the determination of a critical cooling (Phi(c) similar to 600 Ks(-1)) and heating rate (Phi(h) similar to 6 x 10(3) Ks(-1)) for crystallization. Crystallization kinetics was studied in the whole supercooled liquid region by linear heating and isothermal calorimetry. We show that the temperature dependence of crystal growth is reflected in a Kissinger plot for Au49Ag5.5Pd2.3Cu26.9Si16.3 and compares well with a model for crystal growth in a glassy system. Linear heating and isothermal measurements after heating the glass show that its crystallization is always growth-controlled up to its temperature of melting. In contrast, for a low degree of direct undercooling from the equilibrium liquid isothermal crystallization is nucleation-controlled, whereas it is again growth-controlled at large undercooling. The overall crystallization behavior of the metallic glass is presented in a complete time-temperature-transformation map on cooling and, so far not accessible, on heating after various cooling procedures. (C) 2014 AIP Publishing LLC.