Invited Lecture
Diffusion-like mass-transfer in Cu-based alloys during high pressure torsion

The influence of high pressure torsion (HPT) on the formation and decomposition of solid solutions in several Cu-based alloys was studied. The Cu-based binary alloys with were annealed (1) at high temperature close to eutectic temperature T_e where all (or almost all) atoms of a second component are solved in the Cu-rich matrix and (2) at relative low temperature where almost all atoms of a second component were precipitated in form of a particles of a second phase surrounded by an almost pure Cu-matrix. Such samples were subjected to HPT. The competition between deformation-driven precipitation and dissolution of precipitates took place. Steady-state value of the torsion torque is reached already after 1.5-2 anvil rotations. The dynamic equilibrium between precipitation and dissolution appeared. The precipitates in samples (2) partially dissolved in the matrix during HPT. The solid solution in samples (1) partially decomposed. The resulted concentration of a second component after HPT was almost the same in samples (1) and (2). In other words, the equifinal state is reached during HPT. The composition of Cu-matrix in this equifinal state is equal to that which can be reached in equilibrium after long annealing at a certain temperature T_eff. T_eff increases with increasing activation enthalpy of diffusion of a second component. The correlation between activation enthalpy of diffusion of a second component and its melting temperature has been observed. The work has been partially supported by the Russian Foundation for Basic Research (grants 15-53-06008 and 16-53-12007), Deutsche Forschungsgemeinschaft, the Russian Federal Ministry for Education and Science (Increase Competitiveness Program of NUST«MISiS»), National Science Centre of Poland (grant OPUS 2014/13/B/ST8/04247)