Matrix Damage in Iron

ABSTRACTWe present results of a weak-beam transmission electron microscopy study of “matrix damage” in two nearly-pure irons (designated alloys 1A and 2A) produced by neutron irradiation to a fluence of 0.06 dpa at 280°C. The matrix damage in both materials was found to consist of small (2-6 nm) dislocation loops. About 80 % have Burgers vectors b = a<100>, and the remainder have b = a/2<111>. The loops in alloy 1A have a mean image size dmean = 2.8± 0.1 nm and a mean maximum image size dmax = 4.2± 0.3 nm, while those in 2A have d mean = 3.4± 0.1 nm and d max = 4.5± 0.3 nm. The number densities are about 8.5 × 1021 m−3 in alloy 1A, and 6.6 × 1021 m−3 in 2A. It can be shown that the loops can account for the observed irradiation hardening. At least some loops are stable under thermal annealing to temperatures of at least 430°C. This and other indirect evidence suggests that their nature is interstitial.