Effects of hydrogen on the tensile properties of a gamma titanium aluminide sheet at room temperatur

Gamma titanium aluminides are being considered for use in propulsion systems and aerospace structures because of their good high-temperature mechanical properties. However, interactions with hydrogen are of concern due to the adverse effects of hydrogen on conventional titanium alloys. The effects of hydrogen on the tensile properties of a Ti-47Al-2Cr-0.2Si sheet, a gamma titanium aluminide alloy, were investigated at room temperature. Primary annealed (PA) and near-gamma (NG) microstructures of this alloy were analyzed. Scanning electron microscope (SEM) observations of the fracture surfaces were made to determine the mechanisms of fracture of this alloy under the effects of hydrogen. A brief study of the effect of the strain rate on the ductility of hydrogen-precharged samples was also performed. It was demonstrated that the effect of hydrogen on this alloy was more severe for short periods of hydrogen charging, increasing the ultimate tensile strength and the ductility, and decreasing the yield strength of the alloy during the first two and four hours of hydrogen precharging for NG and PA microstructures respectively. The mechanism that governs the fracture on precharged samples is quasicleavage. A ductility maximum was observed at a critical strain rate.