The effect of hydrogen and helium on microvoid formation in iron and nickel

Irradiation experiments on iron and nickel were carried out to study the effect of hydrogen and helium ions on microvoid formation. The total dose was 1.0×1017 hydrogen ions/cm2 (0.2 dpa) and 9.6×1015 helium ions/cm2 (0.3 dpa). The irradiation temperature was 423 and 573 K. To investigate microvoid formation and the total amount of residual defects, positron annihilation lifetime and coincidence Doppler broadening measurements were made. The results for positron lifetime indicated that vacancy clusters grew more easily in nickel than in iron and helium atoms were more effective for microvoid formation than hydrogen atoms. The temperature dependence of microvoid growth was greater after irradiation with hydrogen ions than helium ions between 423 and 573 K in both metals. Annealing experiments for nickel irradiated with hydrogen and helium ions at 423 k were carried out at up to 573 K and the stability of helium–vacancy complexes was clarified.