Influence of displacement damages on deuterium retention in reduced activation ferritic/martensitic steels F82H and Eurofer97

The F82H and Eurofer97 steel samples were irradiated at 300 K with 20 MeV W ions to the damage level of 0.54 displacements per atom (dpa) at the damage peak. Additionally, the F82H steel samples were irradiated at 523 K with 6.4 MeV Fe ions to various damage levels in the range from 0.02 to 12.5 dpa. The damaged samples were exposed to D₂ gas at a pressure of 100 kPa and various temperatures in the range from 373 to 573 K for a certain length of time sufficient to fill ion-induced defects with deuterium. Trapping of deuterium at the ion-induced defects was examined by the D(³He, p)⁴He nuclear reaction with ³He energies between 0.69 and 4.0 MeV allowing determination of the D concentration up to a depth of 7 μm. It has been found that (i) at the damage level above 0.5 dpa, the concentration of the ion-induced defects responsible for trapping of diffusing D atoms does not depend practically on the numbers of displacements per atom, and (ii) the saturation value of the D concentration in the damage zone decreases with increasing D₂ gas exposure temperature, T_exp, and varies from about 10⁻¹ at.% at T_exp = 373 K to 10⁻³ at.% at T_exp = 573 K. The deuterium-trap binding energy is estimated to be 0.7 ± 0.2 eV.