INTERGRANULAR AND TRANSGRANULAR STRESS-CORROSION CRACKING OF CU-30AU

The mechanism of stress corrosion cracking (SCC) of Cu-30Au in 0.6 M NaCl was investigated by a series of experiments in which samples were de-alloyed by potentiostatic anodic polarization at 475 mV (Ag/AgCl) and at zero applied stress (i) for varying lengths of time (10 to 30 min) and then impact bent, and (ii) for 30 min followed by a period of time (5-30 s) at the open circuit potential and then impact bent, and (iii) for 30 min followed by anodic polarization at +150 mV (Ag/AgCl) for a period of time (5-30) and then impact bent. The results indicate that de-alloying at zero applied stress produces a surface layer that is capable for a brief period of time of inducing intergranular cleavage failure of the normally ductile substrate. In addition, samples were de-alloyed and simultaneously stressed at various nominal values (0.5-1.7 sigma(y)). At low values of stress, failure occurred by brittle intergranular cracking, and at high values of stress, failure occurred by brittle transgranular cracking. The results indicate that the electrochemical contribution to the SCC of Cu-30Au in 0.6 M NaCl is the same for both intergranular stress corrosion cracking (IGSCC) and transgranular !;tress corrosion cracking (TGSCC) and that the mode of fracture is dictated by the magnitude of the applied stress.