Hydrogen transport behavior of Timetal-21S alloy

Ti-15Mo-2.7Nb-3Al-0.2Si (Timetal-21S), a metastable β-titanium alloy, is a candidate material for titanium matrix composite structures in hydrogen-fueled hypersonic planes because of its excellent formability and adequate mechanical properties in the 500--800 C temperature range. The alloy is strengthened through the precipitation of fine α particles in the β matrix. The mechanical properties and microstructures are controlled by a solutionizing/aging heat treatment. A major concern in using titanium alloys in hydrogen service is the embrittlement caused by the precipitation of hydrides. It is believed that the large solubility of hydrogen in the β-phase would preclude the precipitation of hydrides in Beta titanium alloys, especially at low hydrogen pressures. However, depending on the hydrogen content, a shift in the ductile/brittle transition temperatures to levels much higher than room temperature has been reported for Timetal-21S alloy. The objective of the present investigation was to determine the hydrogen transport characteristics of the Timetal-21S alloy at moderate pressures up to 6,667 Pa (50 torr) and at temperatures from 400 C to 800 C. A microbalance technique, also referred to as thermogravimetric analysis (TGA), for sorption measurements under ultrahigh vacuum (UHV) conditions was the primary method in this work