HELIUM ION IRRADIATION EFFECTS IN FERRITIC IRON ALLOYS

Available from UMI in association with The British Library.; The effects of 2 MeV He{dollar}sp+{dollar} irradiation in pure Fe and the ferritic alloys Fe-13%Cr and Fe-4%Si have been investigated by the ion channelling backscattering technique at 280K and in the temperature range 20-40K. Channelling measurements have been made for the three major crystallographic axes {dollar}langle110rangle{dollar}, {dollar}langle100rangle{dollar} and {dollar}langle111rangle{dollar} for Fe and Fe-13%Cr and for the {dollar}langle110rangle{dollar} axis in Fe-4%Si at both 280K and 20-40K as a function of the irradiation dose. In all cases the damage, as measured by the backscattering of the channelled beam, tended to saturation at He{dollar}sp+{dollar} doses above 30-40{dollar}mu{dollar}Cmm{dollar}sp{lcub}-2{rcub}{dollar}. However, the initial slopes of the damage-vs-dose curves and the saturation damage levels were considerably bigger for the low temperature irradiations and significant differences were found between the materials studied. Channelling measurements along different axes indicate a sensitivity of the channelled ion flux along different directions, to the irradiation induced defects.; The results indicate that for doses less than 10{dollar}mu{dollar}Cmm{dollar}sp{lcub}-2{rcub}{dollar} the damage produced at low temperature consists mainly of point defects displaced into positions near the channel centres. The Fe-13%Cr and Fe-4%Si alloys show evidence of much less vacancy-interstitial recombination than pure iron.; For high dose irradiation at low temperature, analysis suggests the presence of point defects and vacancy clusters, and dislocation loops considered to be formed through the spatial overlap of separate cascades. Higher damage levels are found in the alloys than in pure Fe which is interpreted as being due to the tendency in these materials for small clusters to form through the trapping of interstitials at Cr or Si atoms.; At room temperature the irradiation induced damage levels in Fe, FeCr and FeSi are considerably smaller than at low temperature which is considered to be due to the greater amount of vacancy-interstitial recombination that can take place at this temperature, and each material shows a high probability for the formation of vacancy clusters.; Thermal annealing measurements have been made after irradiation to low, medium and high doses and indicate that in the absence of vacancy motion, free migration of interstitials leads to formation of interstitial clusters and nucleation of interstitial loops in the Fe-13%Cr alloy. (Abstract shortened by UMI.)...