SOME CHARACTERISTICS OF AQUEOUS STRESS CORROSION IN TITANIUM ALLOYS

Abstract
The influence of microstructural features on the stress corrosion fracture path was studied in the alloys Ti-8Al-1Mo-1V, Ti-6Al-4V, Ti-4Al-3Mo-1V, Ti-5Al-2.5Sn, and Ti-13V-11Cr-3Al by means of optical microscopy, electron microscopy, and X-ray diffraction. These studies showed that susceptibility of titanium alloys to aqueous stress corrosion is influenced by crystalline structure of the susceptible phase (bcc or hcp), preferred grain orientation, and relative phase content where one phase is immune. Stress corrosion cracking occurs on or near the (100) planes in the bcc beta phase, but can only occur near the single (0001) plane in the hcp alpha phase. This restriction of cracking in the alpha phase results in a significant influence due to preferred orientation; it also contributes to the influence of stress state on susceptibility in the high-alpha alloys. The apparent lack of correlation between the structures of the phases and their stress corrosion susceptibilities indicates that the basic mechanism is surface-controlled rather than structurally controlled. (Author)

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