Defects in Decomposing Copper Alloys Studied by Positrons

The evolution of defect structure during isochronal annealing of water-quenched Cu-4.83 at.% In and Cu-4.94 at.% Sn alloys was studied by measuring positron lifetime and Doppler broadening of annihilation line. The behaviour of annihilation parameters in both alloys is found to be analogous. In as-quenched alloys one component of about 180 ps is detected in the lifetime spectra. It remains intact up to the annealing temperature of 450 K and is attributed to positron annihilation at quenched-in vacancies associated with alloying atoms. When going above this temperature, the short component appears in the lifetime spectra, while intensity of the long component starts to drop giving evidence to the reduction of defect concentration. This process is observed to develop up to 550 K; thereafter all annihilation parameters level off. After crossing the phase separation temperature they begin to vary again since the defect structure comes into dependence on cooling conditions. The obtained results are discussed in terms of defect structure evolution in the course of precipitate formation.