Studies of microscopic strains on Alloy 600 surfaces arising from stress-corrosion cracking

Microscopic distributions of elastic and plastic strains have been studied in Alloy 600 during accelerated corrosion. Laue diffraction is employed with a submicron beam of highly coherent polychromatic (white) radiation. The diffraction patterns are analysed to detect elastic and plastic deformations associated with the crack initiation and propagation processes. Stressed C ring and unstressed mill annealed samples of Alloy 600 were corroded under hydrothermal controlled electrochemical conditions. In the C ring, the filamentous surface cracks produced had compressive strain fields along each crack. In the mill annealed sample, changes in strain fields in the same area were measured as oxidation progressed. Cracking at the metal grain boundaries appeared to be induced by expansive growth of surface oxides. For the mill annealed sample, accumulation of elastic strains in the grain boundaries appeared in advance of crack propagation.