Effects of Hydrogen on Cathodically Charged 6Al-4v and 6Al-6v-2Sn Titanium Alloys

Abstract

The αβ-Ti-alloys, like the high strength steels, show a susceptibility to delayed fracture and to hydrogen embrittlement. These similar modes of failure suggest that the same failure mechanism, i.e. diffusion and concentration of hydrogen, is active in both materials. To establish base line information for such a comparison, the replication technique of electron microscopy was used to study the fracture surfaces and microstructures of candidate αβ-Ti alloys cathodically charged with hydrogen. As-received mill annealed samples were studied in addition to cathodically charged specimens so as to eliminate spurious results due to artifacts.Figure la shows the normal microstructure of the as-received 6Al-4V alloy near the surface of the specimen. Figure 1b shows the effect of hydrogen in an approximately 1/128″ deep sub-surface zone of a cathodically charged specimen. Here the matrix substructure was affected while the beta phase became clearly delineated. Beyond 1/128″ from the surface, the matrix interior was unaffected.