The outline of glass transition phenomenon derived from the viewpoint of devitrification process

The glass transition phenomenon in glasses has been studied extensively. However, an important question which is still not completely answered is: do glassy and liquid phases represent the same phase, just observed at different temperatures, or if liquid-glassy phase transformation and vice versa (called glass transition) indeed takes place. Moreover, a thermodynamic aspect of glass transition has been pointed out by Kauzmann. A large number of the recently collected experimental data motivated us to have a closer look at the glass transition phenomenon in metallic glasses from the viewpoint of devitrification of the glassy phase on heating. The formation of a supercooled liquid region and devitrification behaviour of metallic glasses on heating, studied using differential scanning and isothermal calorimetry as well as x-ray diffraction and transmission electron microscopy, are discussed in relation with the glass transition phenomenon. One of the most clear sequences of the glassy-supercooled liquid phase transition is the change of the devitrification behaviour and the kinetics of the devitrification reaction in some alloys after the transition from the glassy to the supercooled liquid state.