Study of the relaxation behaviour of severely deformed bulk metallic glasses

Glasses have been used by people for years and represent an important class of materials, which today are an indispensable part of everyday life. In order to produce a metallic glass, the amorphous melt must be cooled down so quickly that the crystallisation cannot take place. If this succeeds, the amorphous state can be frozen and the metallic glass will have a disordered structure. Metallic glasses are characterised by a high hardness, corrosion resistance, a high elastic limit and good soft magnetic properties. However, metallic glasses have the great disadvantage that they show almost no plastic area. The project consists in studying the relaxation behaviour of a Pd-based alloy, which is the exothermic signal appearing before glass transition, when it is severely deformed by high pressure torsion (HPT). Some indicators manifest that during the relaxation process exothermic events can appear, due to alpha and beta relaxation; these signals will be more or less noticeable depending on the heating rate and the type of deformation applied. The aim is to analyze why these calorimetric signals, which indicate the presence of different relaxation mechanisms that show different sensitivities concerning to the applied pressure (8 GPa) and 5 rotations with the HPT, appear in the relaxation process. Differential Scanning Calorimetry (DSC) and Kissinger analyses shall be employed to determine the activation energies of these peaks, in order to discuss their physical origin and relate them with their corresponding relaxation type.