Positrons as the probe of phase transformations in Cu-Mn alloy

Abstract
The peak counting rates of gamma - gamma angular correlation curves of positron annihilation (PCAC) were measured at thermal equilibrium decreasing stepwise the specimen temperature, for Cu-Mn alloys containing 8.0, 15, 21 and 25 at.% of manganese. For the 8.0 at.% Mn and 21 at.% Mn alloys, no abnormal changes were observed in the temperature dependence of the PCAC other than vacancy effects, but the changes in order-disorder transformation and other phase transition were confirmed in the 15 at.% Mn and 25 at.% Mn alloys. A supplementary experiment by the differential thermal analysis on Cu-25 at.% Mn was in good agreement with the results of positron annihilation. The same measurement of positron annihilation on the Cu-2.3 at.% Ag alloy was performed and the influence of precipitation on the temperature dependence of the PCAC was examined. The apparent formation energies of a vacancy were analysed using the trapping model. The deviation of the PCAC from the trapping model at lower temperatures was deduced by curve fitting using the trapping model.