INTERSTITIAL MIGRATION IN IRRADIATED IRON AND IRON-BASED DILUTE ALLOYS .2. INTERSTITIAL MIGRATION AND SOLUTE TRANSPORT IN FENI, FEMN AND FECU DILUTE ALLOYS

Three series of dilute iron alloys, FeNi, FeMn and FeCu, with concentrations ranging from 50 at.ppm to 3 at.%, have been electron-irradiated at low temperature and annealed up to room temperature. The recovery spectra of the radiation-induced resistivity show that mixed-interstitial migration takes place, in the FeNi alloys, at the beginning of stage II (130-150 K, depending on the Ni concentration), thus providing evidence of the formation of stable mixed-interstitial Fe-Ni during self-interstitial migration in stage I. Mixed interstitials are deduced to be formed also in FeMn and FeCu alloys although they are not stable above stage I and are not directly observable. Mixed poly-interstitials migrate below stage III (i.e. below 200 K) in the three alloys studied. Such a migration instead of break-up results in the growth of larger mixed-interstitial clusters and leads to solute clustering and correlated solute bulk depletion. Bulk depletion was indeed observable in the FeCu and, to a lesser extent, in the FeNi dilute alloys through a diminution of the residual resistivity of the samples. In the FeMn concentrated alloys (1 and 3%), the mixed poly-interstitial clustering gives rise in stage II to gamma -precipitation which largely survives the vacancy migration.