Cryogenic Deformation Behavior of TiAl and Insights Into Embrittlement After High‐Temperature Exposure Combined With Secondary Ion Mass Spectroscopy of Near Surface Chemistry

This study investigates the embrittlement of TiAl after high-temperature air exposure. The loss of room-temperature tensile ductility persists even when tested under liquid nitrogen (−196 °C), with brittle fracture occurring at higher stress levels than typical room-temperature fracture. Existing embrittlement mechanisms in TiAl literature fail to explain this phenomenon under liquid nitrogen. Using secondary ion mass spectrometry (SIMS), surface chemistry analysis of binary TiAl alloys exposed at 700 °C for 4 h in an artificial air-like environment (containing heavy water, $^{15}$N$_2$, and $^{18}$O$_2$) revealed dissociation of water vapor at the TiAl surface and absorption of deuterium into the material. This marks the first report of water vapor dissociation and deuterium (or hydrogen under natural conditions) ingress into heated TiAl specimens. A localized enrichment of hydrogen and deuterium was observed beneath the surface. Given that traditional embrittlement mechanisms do not account for the increased fracture stress under liquid nitrogen, it is proposed that hydrogen absorption during exposure and its near-surface enrichment contribute to embrittlement under these conditions.