Hydrogen induced cracking of Ti-24Al-11Nb at room temperature

Abstract

The effect of hydrogen on a titanium aluminide alloy based on [alpha][sub 2](Ti[sub 3]Al) phase, i.e., Ti-24Al-11Nb (at%) has been investigated by Chu and Thompson. The fracture strain [epsilon][sub f] and the nominal fracture stress [sigma][sub nom], for a wide range of hydrogen concentration, did not decrease when the crosshead speed decreased from 50mm/min to 1.25 [times] 10[sup [minus]5] mm/min. This absence of strain-rate effect means that there is no effect of atomic hydrogen in solid solution in the alloy on [epsilon][sub f] and [sigma][sub nom] measured by using precharged smooth or notched specimens. Hydrogen induced cracking (HIC) could initiate but only propagated a small amount, e.g., 0.01 mm to 0.3 mm, at room temperature for WOL specimens precharged with hydrogen at 500 C, because of low terminal solubility of hydrogen in this alloy in equilibrium with hydride. The K[sub IH] and da/dt of HIC in hydrogen gas at high temperature, e.g., T>400 C, however, could be measured. Can HIC occur and K[sub IH] be measured at room temperature during cathodic charging Although almost all hydrogen will precipitate as hydride at room temperature owing to low terminal solubility of hydrogen, the atomic hydrogen provided continuously during dynamic charging may resultmore » in HIC at room temperature. In this work, therefore, the K[sub IH] of HIC during charging at room temperature was measured. A variety of properties, including UTS, [epsilon][sub f], [sigma][sub nom] and K[sub IH] of this alloy have been shown to be strongly related to microstructure. The other purpose of this paper was to investigate the effect of microstructure on K[sub IH] during charging at room temperature.« less