Stress-Corrosion Characteristics of a Ti-7Al-2Cb-1Ta Alloy Available to Purchase

With only a few exceptions, titanium and its alloys have been considered immune to stress-corrosion cracking in almost all environments at room temperature. It has been shown recently, however, that titanium alloys will fail readily by stress-corrosion cracking when a notched specimen is exposed using the cantilever-beam loading technique. This study reports the stress-corrosion behavior of a Ti-7Al-2Cb-1Ta alloy evaluated using the cantilever-beam testing procedure. The evaluation included effects of applied anodic and cathodic potentials, specimen loading method and presence of hydroxyl ion as inhibitor. When a specimen was loaded in air, stress-corrosion cracking could be almost eliminated by allowing the protective oxide film, ruptured by stress, to heal before adding the electrolyte. Stressing the specimen and thus rupturing the passive film in a chloride environment, however, resulted in a very pronounced susceptibility to stress-corrosion cracking and short times to failure. Potentials more active than -1.3 volts (versus saturated calomel electrode) afforded cathodic protection to the alloy tested, which, surprisingly, appeared to be immune to hydrogen embrittlement. The present studies have shown that the stress-corrosion cracking of this titanium alloy is caused by the rupturing of the protective oxide film followed by stress-corrosion cracking by an active path mechanism.