Effects of high-temperature hydrogen exposure on room temperature tensile properties and fatigue crack growth behaviour of TiAl base alloy

Tensile, notched tensile, and fatigue crack growth tests of hydrogen-exposed (in 0.1 MPa 99.9995% H2 at 800 °C for 6 and 24 h) TiAl base alloy were carried out in ambient air. The results are compared with those of the material before exposure. By the H2 exposure, the tensile ductility and tensile strength were reduced significantly, and greater reduction in the strength of the notched specimen was observed. The H2-exposed specimen fractured in the elastic deformation range, while the non-exposed specimen deformed plastically before fracture. A small compact tension specimen (CT) was used to correlate the fatigue crack growth rate da/dN and stress intensity factor range ΔK. In the near-threshold region of the fatigue crack growth diagram, the H2-exposure had no effect on da/dN. With increasing ΔK, da/dN of the H2-exposed material increased to about ten times higher than before exposure. The acceleration is due to the hydrogen embrittlement (reduction in ductility).