High Temperature Corrosion Behavior of Beta-21S Titanium Alloy

Abstract Advanced Beta-21S titanium alloy is being considered for future high speed aircraft and hypersonic propulsion system applications due to its strength at elevated temperature and formability compare with any intermetallic compounds. The objective of this investigation was to evaluate the high temperature corrosion behavior of the alloy in air, molten salt and hydrogen gaseous environments and compare it with titanium aluminides and iron aluminides intermetallic compounds. This investigation showed that Beta-21S alloy is extremely oxidation resistant below 870°C (1600°F). Above 900°C due to the formation of a volatile molybdenum oxide its oxidation rate increases sharply and in presence of any molten salt severe metal dissolution would be observed. Hydrogen environment embrittlement (HEE) susceptibility of Beta-21S was studied in 34.5 Mpa (5000 psi) hydrogen gas at elevated temperature, no susceptibility to HEE was observed below 150°C, due to the alloy high hydrogen solubility limit (Beta phase titanium alloy). However, severe HEE susceptibility was observed at above 200°C, and titanium was converted to a brittle titanium hydride phase.