Effects of dislocation on thermal helium desorption from iron and ferritic steel

Thermal desorption measurements were performed to investigate helium trapping in α-iron and a reduced activation martensitic steel (RAMS) bombarded at room temperature with mono-energetic He+ ions. Incident energies were both 8 keV and 150 eV. Prior to helium implantation, the samples of α-iron were plastically deformed by rolling at room temperature followed by annealing at 673, 873 and 1073 K for 2, 12 and 2 h, respectively. These samples are hereafter called PR1, PR2 and FA, respectively, and the as-rolled sample is called CW. The dislocation densities of the samples decrease in the order of CW, PR1, PR2 and FA. Thermal desorption spectra show a clear peak at around 800 K, only for the CW, PR1, PR2 and RAMS samples, which may correspond to desorption of helium atoms trapped by dislocations. The effects of dislocations on micro-structural evolution in iron and the steel during helium implantation are discussed.