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Diffusion of helium in magnesium and titanium before and after clustering

Journal of Nuclear Materials
Publication Date
DOI: 10.1016/0022-3115(91)90464-i


Abstract Magnesium and titanium foils were homogeneously implanted by α-particles at room temperature and afterwards helium desorption was investigated during linear heating (0.83 K/s) and isothermal annealing. Desorption started by atomic diffusion with diffusion enthalpies of 0.6 ± 0.1 eV (Mg) and 1.0 ± 0.3 eV (Ti), respectively. For both metals this is consistent with a dissociative diffusion mechanism, but in Ti a vacancy mechanism can not be fully ruled out. After isothermal annealing a temperature dependent fraction of the implanted helium was retained in the specimens due to clustering. Desorption after formation of clusters or small bubbles was compared to models of bubble coarsening. At temperatures from 523 to 653 K in Mg and from 623 to 773 K in Ti, bubble migration by surface diffusion was found to be the dominant coarsening mechanisms characterized by surface diffusion enthalpies of about 0.7 and 0.64 eV, respectively. Helium dissociation from bubbles (Ostwald ripening) was identified as dominant mechanism in Ti from 973 to 1073 K.

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