EFFECT OF HELIUM GAS BUBBLES ON CREEP DUCTILITY OF AN AUSTENITIC ALLOY

Post-irradiation transmission electron microscopy has been performed on a split heat of a high temperature precipitation-hardened alloy (A-286) containing 0.001 wt % and 0.010 wt % natural boron. After annealing at 760, 845 and 955 °C, foils were prepared from sections taken from close to the fracture of specimens creep-tested to failure. The observations were compared with those previously obtained for undeformed specimens. p]Helium gas bubbles were found to be arranged in spherical shells around coarse precipitates believed to be TiN. Any effect of creep deformation on bubble size was masked by the annealing treatment, and the bubble size did not differ systematically from that observed for the undeformed specimens. The measured increase in creep resistance with increasing helium atom concentration is explained in terms of a reduction of dislocation mobility. It is suggested that the reduced ductility and associated reduction in strain rate sensitivity after irradiation may be very sensitive to the gas bubble distribution. The observation of bubbles on dislocations lying in the boundaries may be particularly significant. © 1969.