Positron annihilation spectroscopy of vacancy type defects in submicrocrystalline copper under annealing

The annealing of submicrocrystalline copper produced by the equal channel angular pressing followed by rolling was studied using positron annihilation and XRD analysis. In as-prepared samples, positrons are trapped at vacancies, concentration of which is very high (∼1.6 × 10−4) and dislocation type defects; however, a few percent of positrons annihilate from a free state. Increasing annealing temperature leads to the formation of vacancy complexes. The main positron trap centers in the temperature range ΔT = 20–300°C are vacancies and their small complexes of two or three vacancies. The dominant centers of positron trapping in the temperature range ΔT = 300–670°C are dislocation-type defects.