Invisible and visible point defect clusters in neutron irradiated iron

Microstructure evolution in a low-dose neutron-irradiated iron was examined with a transmission electron microscope (TEM). The characteristics of the temperature dependence of defect structures in irradiated iron were as foll ows, (a) rather lower number density of defect dusters at 473 K than at 573 K, (b) development of dislocation loops and voids at an intermediate tempe rature of 623 K and (c) formation of irregularly shaped dislocation loops a t 673 K, Comparing the defect structures produced by the irradiation with a conventional temperature control and that with an improved temperature con trol, nucleation of defect dusters was suppressed under neutron irradiation at 473 K. From the defect structures introduced by irradiations in which t he irradiation temperature was cyclically changed between two temperatures (T-cycle irradiation), the accumulation of a large number of invisible vaca ncy type defect clusters by irradiation at 473 K was strongly suggested. (C ) 1999 Elsevier Science B.V. All rights reserved.