Microscopic Cracking on Flat Alloy 600 Surfaces Following Accelerated Caustic Corrosion: Mapping of Strains and Microstructure During the Corrosion Process

Microscopic distributions of elastic and plastic strains have been studied at three intervals during an electrochemically accelerated corrosion test of a flat, polished surface of a mill-annealed and unstrained sample of Alloy 600 (UNS N06600) in 10% sodium hydroxide (NaOH) at 315 degrees C. Laue microdiffraction was used with a micron-sized polychromatic (white) x-ray beam to map strain changes in the sample as a function of corrosion time. After two 12 h corrosion periods, tensile elastic strains were detected along a grain boundary. After a third 24 h corrosion period, this particular boundary was found to have cracked to a depth of several microns; other adjacent boundaries exhibited tensile elastic strain, but no cracking. No significant changes to plastic strain distributions in the same area could be detected as a function of corrosion exposure.