Interstitial migration in irradiated iron and iron-based dilute alloys. II. Interstitial migration and solute transport in FeNi, FeMn and FeCu dilute alloys

Abstract

For pt.I see ibid., vol.2 no.47, p.9269-90, 1990. 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.