Internal hydrogen embrittlement of solution heat treated and aged Ti-15V-3Cr-3Al-3Sn and Ti-15Mo-3Nb-3Al
- Univ. of Virginia, Charlottesville, VA (United States)
The effects of electrochemically introduced hydrogen on the room temperature mechanical properties of two B titanium alloys, Ti-15V-3Cr-3Al-3Sn and Ti-15Mo-3Nb-3Al are compared. Solution heat treated (SHT), peak aged (PA), and duplex aged (DA) conditions are investigated using notched tensile bars and Bridgman`s analysis of longitudinal stress and average effective plastic strain. Ti-15Mo-3Nb-3Al is more susceptible to hydrogen embrittlement than Ti-15V-3Cr-` 3Al-3Sn based on reductions in longitudinal stress, plastic strain, and changes in fracture mode at hydrogen concentrations above 1,000 wt. ppm. Hydriding of the {alpha} and {beta} phases was not observed over the range of hydrogen concentrations investigated. Instead, changes in fracture paths with hydrogen are correlated with deformation behavior and {alpha} precipitation. The susceptibility of Ti15Mo-3Nb-3Al is attributed to a high temperature, long time solution treatment which affects deformation behavior in the SHT condition and promotes grain boundary a precipitation in the PA condition. The high temperature solution treatment removes a nucleation sites from grain interiors and promotes planar slip. Subsequent {alpha} precipitation occurs preferentially on {beta} grain boundaries and, lastly, in grain interiors resulting in fine intragranular precipitates. It is hypothesized that fine intragranular {alpha} plates as well as aligned boundary {alpha} colonies are readily sheared and also promote planar slip in the PA condition. In contrast, a lower temperature, shorter duration solution treatment for Ti-15V-3Cr-3Al-3Sn results in wavy slip and more homogeneous, slightly coarser {alpha} precipitates upon aging, which may be less prone to slip localization by dislocation shearing. Localized planar slip and grain boundary {alpha} colonies are believed to promote both internal hydrogen embrittlement and aqueous environmentally assisted cracking. 67 refs.
- OSTI ID:
- 70152
- Report Number(s):
- CONF-940222--
- Country of Publication:
- United States
- Language:
- English
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