Grain Boundary Migration and Growth of Gas Bubbles in Neutron Irradiated Al-Li Alloys

Abstract

The electron microscope has been used to observe the behavior of He gas bubbles in cold-worked Al-Li alloys upon post-irradiation heating. The bubbles appeared occasionally along the grain boundary in the A1-2.7w/0 Li specimen irradiated to 4.1×10¹⁹n/cm2 and then heated to about 300°C. Upon beating to higher temperatures, up to 450°C, the bubbles in the specimen grew along with the gradual growth of the recrystallized grains. When the bubbles reached sizes of 0.3-0.6μ, upon beating to 500°C, the grain boundaries migrated, leaving the bubbles detached from them. In the Al-0.4w/0 Li specimen, the bubbles migrated out of the specimen surface, along with the grain boundary, upon heating to the temperatures above 450°C. The grain sizes of the irradiated Al-2.7w/0Li specimen heated for 1 hr to 450°C were smaller than in unirradiated specimen heated for 1 hr to 400°C.
In the displacement of grain boundary caused by grain growth, the gas bubbles are swept together to form larger bubbles until they reach a certain critical size. And as the bubbles become larger, they detach from the moving boundary. The bubbles impede the grain boundary movement, but do not suppress it completely. The bubbles found on the grain boundaries differed in shape from the bubbles that had grown in the grain interior.