The effect of strain-rate upon stress corrosion crack velocity in α-brass in ammoniacal solutions

Stress corrosion crack velocity in a-brass has been measured as a function of tensile crosshead speed and solution composition in aqueous solutions, mainly at pH 6.8. At low crosshead speeds the velocity was constant but at crosshead speed values high enough to cause general yielding the velocity increased with crosshead speed in a double logarithmic relationship. The maximum velocity producing 100 % intergranular fracture was ca. 30 mm/h. Potentiostatic experiments indicated an increase in crack velocity with anodic polarization but only within the potential/pH region where Cu2O was stable. At more noble potentials the crack velocity was lower, an effect seen also with cathodic polarization and with the addition of chloride and bromide ions, and in all cases the fracture was partly transgranular. The important factor controlling both the type and amount of stress corrosion cracking is the ratio of tarnish film formation rate/crack tip strain-rate.