EFFECT OF TENSILE-STRESS ON THE GROWTH OF HELIUM BUBBLES IN AN AUSTENITIC STAINLESS-STEEL

Foils of the ternary alloy, Fe-17 wt% Cr-17 wt% Ni, were cyclotron-injected with ~160 at ppm helium and annealed at 1023 K for times up to 1.74 Ms (482 h). Some foils were subjected to tensile stresses which ranged from 9.8 to 27.5 MPa during annealing while others were unstressed. Helium bubbles grew in unstressed specimens at different rates depending on their location in the microstructure; the largest bubbles were found at triple grain junctions, smaller ones on the grain boundaries, and the smallest in the grain matrices. Bubble size in the matrix was approximately proportional to t 1 4 for annealing times greater than 2.88 × 104 s (8 h). Applied tensile stress accelerated the growth of bubbles, especially at triple grain junctions and grain boundaries. The enhanced growth in these areas appear to be associated with grain-boundary sliding. The number of bubbles in the matrix and on grain boundaries generally decreased with annealing time, suggesting that a migration-coalescence mechanism was also operating. © 1979.