Atomic structure of Cu-Zr-Ti metallic glasses subjected to high temperature annealing

An influence of high temperature annealing process (before crystallization) on the atomic structure of two different as-prepared ribbon Cu-Zr-Ti metallic glasses (Cu60Zr20Ti20 and Cu55Zr16Ti29, at.%) was experimentally studied by means of differential scanning calorimetry and in situ hard X-ray diffraction. Results of our experiments prove different atomic structure and behaviour of the glasses upon the annealing. Special emphasis is placed on the thermally activated effects which precede the crystallization. During the annealing, both glasses initially show with elevated temperature continuous short and middle range order thermal expansion and an overall decline of the atomic structure ordering. But above a temperature, which can be slightly different for every mean atomic neighbour (or every atomic coordination shell), one can observe a change in behaviour of the glasses: the glasses modify the thermal expansion rate of most of the mean atomic neighbours' distances and show a tendency to increase the degree of ordering of the atomic structure. Both these effects are more pronounced for Cu55Zr16Ti29. Therefore, as a result of the metallic glasses' different behaviour in the annealing, near the crystallization temperature Cu55Zr16Ti29 commonly shows larger relative elongation of the mean atomic neighbours' distances (larger thermal expansion) than Cu60Zr20Ti20. Moreover, Cu55Zr16Ti29 exhibits contrary to Cu60Zr20Ti20 an increase of the degree of ordering of the atomic structure if compared with the initial as-prepared state at the beginning of the experiment.