ROLE OF SOLUTE ATOMS ON MICROSTRUCTURAL EVOLUTION IN NEUTRON-IRRADIATED NICKEL

Fission reactor irradiation of nickel alloys with solutes of widely varying volume size factors 2 at % of Si, Cu, Ge and Sn, was performed for a wide range of irradiation temperature. At a lower temperature 473 K, a high density of small vacancy clusters are mixed with interstitial-type dislocation loops in all the alloys. At higher temperatures, in the alloys with solutes of negative volume size factor, Si, and extremely large positive factor, Sn, the unfaulting of interstitial-type dislocation loops during irradiation is suppressed, and the development of dislocation structures is moderate. In the alloys with solutes of positive but not large volume size factor, Cu and Ge, including pure Ni, unfaulting of loops strongly promotes the development of dislocation structures. As a consequence of the difference in these dislocation structure developments, void formation is almost completely suppressed in the first category and is enhanced strongly in the second.