Neutron irradiation embrittlement of polycrystalline and single crystalline molybdenum

Neutron irradiation-induced ductile-brittle transition behaviour of carburized molybdenum polycrystals and single crystals has been studied. These specimens were irradiated at 673, 873 and 1073 K to (7.9-9.8) x 10(23) n/m(2) (E greater than or equal to 1 MeV). The results were analyzed as the difference in the behaviour between polycrystals and single crystals, and the : effects of irradiation temperature. Three-point bend tests showed that the neutron irradiation-induced shift of ductile-brittle transition temperature (DBTT) at each irradiation temperature was much larger in single crystal specimens than in polycrystal ones. The carburization treatment was found to be more effective in polycrystals rather than in single. crystals. This suggests that in polycrystals the grain boundary interface is strengthened due to carbon addition. At higher irradiation temperatures, this shift of DBTT decreased in both the specimens. It is characteristic in post-irradiation fracture behaviour than in single crystal specimens the cracks initiated from the island grains on the specimen surface. (C) 1998 Elsevier Science B.V. All rights reserved.