Structural aspects of deformational amorphization of Ti$_{50}$Ni$_{25}$Cu$_{25}$ crystalline alloy under high pressure torsion

The evolution of the structure of the Ti$_{50}$Ni$_{25}$Cu$_{25}$ crystalline alloy during high-pressure torsion at room temperature has been studied. The torsional moment variation curve as a function of the strain value was fixed in situ, which allowed directly observing the transition of the material from the crystalline state to the amorphous state during the HPT. It was found that the amorphization of the material in the course of the HPT begins on the grain boundaries and fragments of the crystalline phase. Amorphized boundaries form a “grain-boundary carcass” in the cells of which the high-defect nanocrystalline phase is formed. Growth of deformation leads to broadening of the “grain-boundary carcass,” loss of stability of the crystalline phase, and, as a consequence, to the phase transition "crystal $\to$ amorphous" state.