Reactions and Kinetics of Newly Generated Titanium Surfaces and Relevance to Stress Corrosion Cracking

Instrumentation is described for obtaining current-time curves for new metal surfaces produced by fast fracture in electrolytes under potentiostatic conditions. Measured anodic current densities for titanium specimens in acid solutions decayed about a million fold in a time of 10⁻⁴ to 10³ seconds at which steady state was approached. Analysis of the experimental data indicate the actual initial current density for anodic dissolution is more than 10 A/cm² in 3M HCl and may be orders of magnitude greater. Thus stress corrosion crack propagation by an anodic process in titanium cannot be ruled out. Formation of metal salt films would be predicted at high anodic current densities in cracks. Calculations show that formation and growth of a salt film in the tip region would give a rapidly decaying current density moving away from the tip which would keep the tip sharp. This phenomenon may be called the electrochemical knife.