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As part of a larger effort to study the influence and possible synergisms involving solutes, helium and cold working, a simple quaternary alloy representing AISI 316 without solutes was irradiated in the Oak Ridge Research Reactor (ORR). This alloy's composition is Fe-17Cr-16.7Ni-2.5Mo and is designated P-7 or “pure 316.” It was irradiated at 350, 550, and 650°C in each of the following conditions: annealed, 20 percent cold worked, annealed plus helium implanted, 20 percent cold worked plus helium implanted and various annealed or cold work plus implanted and aged conditions. The implanted specimens contained a range of helium concentrations injected at ambient temperatures. All specimens chosen for examination by electron microscopy and immersion density were irradiated to 3 to 5 dpa.
In agreement with an earlier microchemically-based prediction it was found that both the volume and density of voids were insensitive to cold work in an alloy lacking minor solutes such as silicon and carbon. This finding is inconsistent with most theoretical treatments of the effect of cold work on swelling in commercial alloys. The high density of dislocations after cold working has been thought to be responsible for the reduction of point defect concentrations and subsequent void nucleation. While the preinjection of 30 appm helium appeared to suppress visible swelling, this may be an illusion related to resolution problems in imaging very small voids. Both density change measurements and postirradiation aging studies indicate that swelling may exist in the preinjected specimens in the form of unresolvable cavities.
swelling, microchemistry, solute effects, cold work, helium, Fe-Cr-Ni-Mo alloy, neutron irradiation, microstructure, AISI 316
Senior Research Engineer, Hanford Engineering Development Laboratory, Richland, WA
Fellow Scientist, Hanford Engineering Development Laboratory, Richland, WA