The effects of hydrogen on the deformation and fracture behavior of the metastable beta-titanium alloy, TIMETAL(RTM) 21S
The metastable $\beta$-titanium alloy, TIMETAL$\sp\circler$ 21S, exhibits a sharp ductile-to-brittle transition when the hydrogen concentration is increased slightly above H/M $=$ 0.22. To understand this sharp transition, a series of experiments was devised to test for the possible hydrogen embrittlement mechanisms. In situ straining experiments in an environmental cell TEM showed that hydrogen enhances the mobility of dislocations. However, this mechanism cannot account for the abrupt transition that is observed. No evidence for the formation of hydrides on fracture surfaces or in the stress fields of active cracks was found suggesting that the stress-induced hydride mechanism is not responsible for the observed transition. Therefore, the most viable mechanism is hydrogen-induced decohesion. Bulk testing showed that internal hydrogen reduces the yield strength of ductile specimens and decreases the fracture stress of the brittle specimens. All of the observed phenomena are consistent with a decohesion mechanism.
Engineering, Metallurgy, Engineering, Materials Science
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign