In situ observation of the “crystalline⇒amorphous state” phase transformation in Ti2NiCu upon high-pressure torsion

The evolution of the structure and mechanical behavior upon deformation has been studied experimentally in situ by room-temperature high-pressure torsion (HPT) of the initially crystalline Ti2NiCu alloy. An abrupt increase in the shear stress upon HPT has been revealed. It was found that the observed effect is due to the deformation-induced “crystalline⇒amorphous state” phase transformation and the corresponding change in the mechanism of severe plastic deformation. It is shown that the amorphization of the material begins at the boundaries of grains and fragments of the crystalline phase as a result of grain boundary sliding processes. It was established that the amorphous boundaries form a “grain-boundary framework”, which upon deformation is expanded and transformed into bulk amorphous phase.