Fracture mechanism of TiAl intermetallics caused by hydride and atomic hydrogen

Hydrogen embrittlement (HE) of TiAl intermetallics was studied at room temp erature. The results showed that there were two forms of HE in TiAl interme tallics, i.e. hydride HE and atomic HE. Most of hydrogen in TiAl intermetal lics was transformed into hydrides at room temperature. The hydride exists as (TiAl) H-x for a low hydrogen concentration while it exists in several f orms for a higher hydrogen concentration. Stress intensity factor K-IC decr eased with increase in hydride concentration. K-IC decreased further when T iAl intermetallics were charged cathodically with hydrogen in 1 mol/L H2SO4 solution. Stress intensity factor during hydrogen charging K-IH was about 50% K-IC. 20% of the decrease was caused by hydrides while 30% was caused b y atomic hydrogen. Mechanism of HE caused hydrides was the same as any othe r second phase in nature. Delayed fracture caused by atomic hydrogen result ed from hydrogen induced local plastic deformation.