In Situ Investigation of Intergranular Stress Corrosion Cracking Initiation and Coalescence and Effects of Geometric and Microstructural Characteristics

This work is concerned with the mechanism of intergranular stress corrosion cracking (IGSCC) initiation and coalescence of thermally sensitized Ni alloy using in situ optical microscopy and electron backscatter diffraction (EBSD). The in situ observation was performed on the side surface of a C-ring specimen during a corrosion test in sodium tetrathionate solution. The geometric and microstructural factors at the grain boundary (GB) such as plastic strain, normal/residual stress, and GB characteristics were measured on the observation area by EBSD before and after deformation of the C-ring specimen. The cracking behavior of the grain boundary monitored from the in situ observation along the cracking path was compared with EBSD-derived parameters such as local misorientation, Schmid factor, Schmid factor mismatch, and GB characteristics; and geometric and microstructural factors such as plastic strain, normal/residual stress, and GB characteristics. From analysis of the distribution of EBSD-derived parameters of the cracked and the intact GBs, dominant factors playing an important role in each cracking step are discussed in terms of local strain, normal/residual stress, and grain boundary characteristics.