A THEORY OF TRANSGRANULAR STRESS-CORROSION CRACKING

A model is proposed to explain transgranular stress-corrosion cracking (T-SCC) in f.c.c. materials, wherein selective dissolution at the crack tip has the effect of lowering the K(Ic) for cleavage. Crack propagation is shown to be anisotropic, with {110} [001] growth being discontinuous due to crack arrest by dislocation blunting. Renucleation involves active dissolution of slip planes at the crack tip which changes the stress state at critical Lomer-Cottrell locks causing them to fail by cleavage. Crack growth in directions away from {110} [001] is continuous. When the crack is propagating, its instantaneous velocity is essentially independent of growth direction. The system studied was Cu-25% Au in 0.6 M NaCl solution at potentials between 300 and 430 mV (s.c.e.), which precludes hydrogen embrittlement.