Mechanical properties in different environments, including oxygen, vacuum, air and H2 environments, of a high Nb-containing TiAl alloy with the composition of Ti-45Al-8.5Nb-(W, B, Y) have been investigated in this work. Fracture behavior in different environments are evaluated and correlated with microstructure of the experimental alloy. The fracture strength and elongation at break of Ti-45Al-8.5Nb-(W, B, Y) in different environmental medium are 598.4MPa/4.18% (O2), 539.6 MPa /3.67% (vacuum), 499.1 MPa /2.77% (air) and 441 MPa/2.27, respectively. Fractography analysis indicates that the experimental alloy exhibits a typical transgranular cleavage fracture in each environmental media. Based on the results of microstructure investigations, it is found that cracks initiation and propagation always take place on boride/matrix and the β phase/matrix interfaces of Ti-45Al-8.5Nb-(W, B, Y) in all environmental conditions. It is also found that the microstructure morphology and the
volume fraction of γ phase play an important role on the environmental embrittlement of the experimental Ti-45Al-8.5Nb-(W, B, Y) alloy.