Abstract
The Ti-24Al-llNb (Ti-24-11) alloy heat-treated to the fine basketweave microstructure was shown previously to be hydrogen-tolerant. In order to assess its limit of hydrogen tolerance, the tensile, creep, fracture toughness, and sustained-load crack growth behaviors of this alloy were studied as a function of hydrogen content. All test specimens were charged thermally with internal hydrogen and tested at 25 °C and 600 °C. Coupon specimens were used for developing the hydrogen-charging procedures and for studying compatibility of the alloy with high-temperature, high-pressure gaseous hydrogen. The mechanical test results indicated that the fine basketweave microstructure was tolerant to hydride embrittlement for hydrogen contents up to ≈1500 wppm. On the other hand, hydrogen charging experiments indicated that the Ti-24-11 alloy was severely cracked and pulverized under zero load when the hydrogen content exceeded 3000 wppm. X-ray diffraction (XRD) results revealed that the dichotomous behaviors might be due to the formation of face-centered cubic (fee) δ-type hydrides at higher hydrogen contents but face-centered tetragonal (fct) γ-type hydrides at lower hydrogen contents. Thus, hydrogen embrittlement in the Ti-24-11 alloy with the fine basketweave microstructure depends on hydrogen content and the nature of hydrides formed.
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