Irradiation assisted stress corrosion cracking of austenitic stainless steels

Samples of ultra high purity stainless steel have been fabricated into 2mm x 2mm rectangular bars and irradiated to one dpa (∼l x 1019 p+/cm2) using 3.4 MeV protons (>20μA) while controlling the sample temperature at 400 degree C. Samples are pressed onto a water-cooled and electrically heated copper block with a thin layer of Sn in between to improve thermal conductivity. The irradiation produced a significant prompt radiation field but sample activation was limited to β-decay and this decayed rapidly in less than 48 h. Samples were hydrogen charged and strained at slow rates at -30 degree C insitu in the Auger electron spectrometer to successfully fracture several samples intergranularly for grain boundary composition analysis. An ultra-high purity (UHP) alloy of Fe-19Cr-9Ni was irradiated to 1 dpa at 400C ± 5C and 7 x 10-9 torr in the tandem accelerator of the Michigan Ion Beam Laboratory, resulting in a dislocation network density of 1.8 x 109 cm2 and a dislocation loop density of 7 x 1016 cm-3 along with the dissolution of small precipitates present in the unirradiated sample. EPR experiments on the UHP irradiated alloy showed no significant increase in charge passed upon reactivation, over an unirradiated sample experiencing the same thermal history. An SCC waterloop and autoclave system has been completed and a sample has been designed to measure the susceptibility of the irradiated microstructure as compared to the unirradiated microstructure