Study of cavities in a creep crack growth test specimen

Small Angle Neutron Scattering (SANS) and Scanning Electron Microscopy (SEM) have been used to determine the degree of cavitation damage, of length scale 5-300 nm, associated with a creep crack grown in a compact tension specimen cut from a Type 316H stainless steel weldment. The specimen was supplied by EDF Energy as part of an extensive study of creep crack growth in the heat affected zone of reactor components. The creep crack propagates along a line 1.5 mm away from, and parallel to, the weld fusion line boundary before deviating away into parent material. The SANS results show a systematic increase in fractional size distribution of cavities approaching the crack, along lines normal to the crack line, and along lines parallel to the crack line approaching the crack mouth. Both SANS and quantitative metallography measurements using SEM indicate two populations of cavities: smaller cavities of less than 100 nm size having a mean diameter of about 60 nm, and a population of larger cavities of 100-300 nm size with a mean diameter of about 200 nm.