Moisture induced environmental embrittlement of a high Nb containing TiAl alloy

This work investigates the mechanical properties in moisture and air environments of a Ti-45Al-8.5Nb-(W, B, Y) high Nb-containing TiAl alloy. The experimental alloys with nearly lamellar, gamma phase increased nearly lamellar and fully lamellar are selected to illustrate the microstructure related environmental sensitivity of mechanical properties. The results give evidence that the experimental high Nb-containing TiAl alloys with different microstructures can be affected by environmental embrittlement, which results in the decrease of mechanical properties in moisture environment. According to the contrast experiments, mechanical properties of fully lamellar alloy decrease significantly, while the performance of gamma phase increased alloy is the most stable one in both air and moisture environments. Fracture morphology characteristics display that transgranular cleavage fracture is the dominant fracture mode and primarily independent of the environmental media. The different performance of experimental alloys indicates that the morphology of γ phase determines the environmental embrittlement of the experimental high Nb-containing TiAl alloy. In addition, the determining factors and the corresponding mechanism of the observed environmental brittleness are also discussed in this work.