Microstructure Sensitivity on Environmental Embrittlement of a High Nb Containing TiAl Alloy under Different Atmospheres

Mechanical properties in different atmospheres, including oxygen, vacuum, air and H₂, of high Nb containing TiAl alloys with the compositions of Ti–45Al–8.5Nb–(0.2W, 0.2B, 0.02Y) have been investigated in this work. Three different microstructure types, nearly lamellar, gamma phase increased nearly lamellar and fully lamellar are selected for revealing the microstructure sensitivity of environmental embrittlement. The results show that the three types of microstructures are all affected by the hydrogen–induced environmental embrittlement. Although the fracture mode of the experimental alloy is cleavage fracture in all atmospheres, the proportions of transgranular and intergranular fractures are different, especially comparing the fracture surfaces in oxygen and hydrogen. Performance comparison results show that the nearly lamellar microstructure is the most susceptible to the hydrogen–induced environmental embrittlement, while the gamma phase increased microstructure is the most stable one; the fully lamellar microstructure results in moderate susceptibility to the atmospheres. Combined with the hydrogen absorption kinetic analysis, it indicates that γ phase at the interface of lamellar colony significantly inhibits the hydrogen–induced environmental embrittlement, while the effect of β phase is just the opposite. In addition, the correlation between microstructure and hydrogen–induced environmental embrittlement is revealed and the corresponding mechanism is also discussed in this work.