Phase transitions in Cu-based alloys under high pressure torsion

Severe plastic deformation not only leads to grain refinement but also accelerates mass-transfer and drives phase transformations in these Cu-based alloys. This review is devoted to the dynamic equilibrium between decomposition of (supersaturated) solid solution and dissolution of precipitates during high pressure torsion (HPT) of diluted Cu-based Cu-X alloys. The precipitation of second phase particles from a solid solution and their dissolution take place simultaneously and compete with each other. During HPT, a certain steady-state concentration Cs of a second component in a solid solution is reached, as if a sample would be annealed at a certain effective temperature Teff. We found that Teff linearly increases with increase of activation enthalpy of bulk tracer diffusion HD. The correlation between activation enthalpy of bulk tracer diffusion HD and melting temperature Tm of diffusing alloying component has been found for the first time. As a result, Teff linearly increases with increase of melting temperature Tm of diffusing alloying component as well. The observed correlations allow one for the first time to predict the behaviour and phase transitions in the Cu-based alloys under high pressure torsion.