Phase transformations in copper–tin solid solutions at high-pressure torsion

Phase transformations of some Hume-Rothery phases (electron compounds) to others in a copper-tin system subjected to high-pressure torsion were detected in our previous work [B.B. Straumal et al., JETP Lett. 100, 376 (2014)]. In particular, the torsion of the $\zeta+\epsilon$ phase mixture at high pressure led to the formation of the $\delta+\epsilon$ phase mixture, as after long-term annealing in the temperature interval $T_{\mathrm{eff}}=350$–$589^\circ$ C. In this work, it has been shown that the high-pressure torsion of $\alpha$-solid solutions of tin in copper results in the final stable solid solution whose composition is independent of the composition of the initial $\alpha$ phase before high-pressure torsion. The final composition is the same as after long-term annealing at the temperature $T_{\mathrm{eff}}=(420\pm10)^\circ$ C. The rate of high-pressure torsion-induced mass transfer is several orders of magnitude higher than the rate of conventional thermal diffusion at the treatment temperature $T_{\mathrm{HPT}}$ and is close to values at $T_{\mathrm{eff}}$. This occurs because high-pressure torsion increases the concentration of lattice defects and this increase is in turn equivalent to an increase in the temperature.