Investigation on the deformation mechanisms and size-dependent hardening effect of He bubbles in 84 dpa neutron irradiated Inconel X-750 micro-tensile specimens

Abstract

Abstract Two micro-tensile tested specimens from 84 dpa neutron irradiated Inconel X-750 alloys at different temperature ranges, 120-280°C and 300–330 oC respectively, were characterized using transmission electron microscopy (TEM). Dislocation slip was found responsible for the failure of the specimen during micro-tensile testing and the significant helium bubble elongation. Helium bubbles were elongated to a minimum size of ∼2.4 nm measured along the minor axis. Some helium bubbles were found elongated on both the primary and an adjacent secondary {111} plane, which is likely due to the occurrence of cross slip of screw dislocations. Nano-twins were also found adjacent to the shear failure surface but no elongated bubbles were found within the nano-twinned region in the high temperature specimen. Based on the dispersed barrier hardening model, individual obstacle strengthening factors of the microstructural features, including gamma prime, helium bubbles, Frank loops, and small defect clusters are computed. The obstacle strength of He bubbles was found to be size-dependent and a critical size was determined, i.e., for bubbles 6.6 nm. The obstacle strength of gamma prime precipitates was calculated to be approximately 0.5.