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A study of neutron irradiation damage in α-iron with magnetoacoustic and Barkhausen emission

Magnetoacoustic emission (MAE) and Barkhausen emission (BE) in α-iron are sensitive to the presence of precipitates and of dislocations. These techniques have been used to examine radiation damage and post-irradiation recovery processes in α-iron containing low levels of interstitial impurities in the annealed and cold-worked conditions, both before and after neutron irradiation at 60 °C to 2.9 × 1019 n cm-2 (greater than 1 MeV). Irradiation leads to the suppression of domain wall pinning in annealed material, as indicated by reductions in low-field BE and MAE activities. Furthermore, cold-worked irradiated α-iron exhibits reduced thermal stability during post-irradiation annealing in the temperature range 250-550 °C, compared with the unirradiated annealing response. The results are interpreted in terms of radiation-induced dissolution of α"-Fe16N2 and γ'-Fe4N nitrides, solute-point defect trapping/dissociation, and enhanced dislocation recovery processes. The studies demonstrate that BE and MAE measurements can provide new information to complement more conventional examination methods for characterization of low-dose irradiation effects in α-iron. The techniques show promise for non-destructive examination of ferrous materials in neutron-radiation environments.