Microstructural examination of neutron, proton and self-ion irradiation damage in a model Fe9Cr alloy

Abstract

Transmission electron microscopy (TEM) was used to compare the microstructural defects produced in an Fe9Cr model alloy during exposure to neutrons, protons, or self-ions. Samples from the same model alloy were irradiated using fission-neutrons, 2 MeV Fe+ ions or 1.2 MeV protons at similar temperatures (∼300 °C) and similar doses (∼2.0 dpa). The neutron-irradiated alloy contained visible interstitial dislocation loops with b = 111, and on average ∼5 nm in size. The density varied from 2±1 × 1020 m-3 (in the matrix far from dislocations and boundaries) to 1.2±0.3 ×1023 m-3 (close to helical dislocation lines). Chromium α′-phase precipitates were also identified at a density of 7.4±0.4 ×1023 m-3. Self-ion irradiation produced mostly homogeneously distributed dislocation loops (6–7 nm on average), and with a greater fraction of 100 loops (∼40%) than was seen in the neutron-irradiated alloy, and at a density of 6.8±0.8 ×1022 m-3. In contrast to the loops produced by neutron irradiation, the self-ion irradiated Fe9Cr contained only vacancy-type loops. Chromium also remained in solution. Proton-irradiated Fe9Cr contained interstitial dislocation loops close to helical-dislocation segments, similar to the neutron-irradiated sample. Chromium α′-phases were also identified in the proton-irradiated sample at a density of 2.5±0.3 ×1023 m-3, and large voids (up to 7 nm) were found at a density over 1022m−3. Like the neutron-irradiated sample, the density of dislocation loops was also heterogeneously distributed; far from grain boundaries and dislocation lines the density was 2.5±0.4 ×1022 m-3, while close to helical dislocation lines the density was 8.1±1.3 ×1022 m-3.