High-resolution, in-situ, tomographic observations of stress corrosion cracking

This chapter presents high-resolution X-ray tomographic observations of intergranular stress corrosion crack nucleation and growth. The tomographic experiment was performed at the European Synchrotron Radiation Facility in Grenoble on the high-resolution tomographic beam-line. Two materials were selected for investigation. These were aluminum alloy 5083, sensitized by ageing at 150°C for 7 days and 302 stainless steel, solution treated at 1050°C for 30 min and sensitized for 1 h at 650°C. Surface examination of samples exposed for 3 h under tensile stress, revealed localized corrosion sites that were longitudinally aligned parallel to the stress axis. Bending the sample caused transverse and longitudinal cracks to open, which appeared to link the longitudinally aligned corrosion sites. The morphology of pitting and cracking is influenced by the aligned microstructure of the AA5083 wrought plate. The initiation of intergranular stress corrosion cracking (SCC) and specimen failure due to crack coalescence is recorded. Segmentation by thresholding can be used to separate the cracks from the matrix. Conventional two-dimensional sections of the data imply that the crack is discontinuous. However, three-dimensional visualization of the same region shows that the crack is, in fact, continuous. © 2008 Elsevier Ltd All rights reserved