Phase Transformations in Copper—Tin Solid Solutions at High-Pressure Torsion

Abstract

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 ζ + e phase mixture at high pressure led to the formation of the δ + e phase mixture, as after long-term annealing in the temperature interval Teff = 350–589°C. In this work, it has been shown that the high-pressure torsion of α-solid solutions of tin in copper results in the final stable solid solution whose composition is independent of the composition of the initial α phase before high-pressure torsion. The final composition is the same as after long-term annealing at the temperature Teff = (420 ± 10)°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 THPT and is close to values at Teff. 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.