Microstructure inducement of different tensile fracture mechanisms at 800 ℃ of directional solidified Ti-45Al-5Nb alloys produced by electromagnetic confinement

Abstract

Directional solidified TiAl alloys have low density and good comprehensive high temperature performance, which is an ideal substitute material for high temperature structural parts. In this paper, Φ 16.5 mm directional solidified Ti-45Al-5Nb sample with full-lamellar microstructure was prepared successfully by electromagnetic confinement technique at 10 µm/s and relative tensile tests at 800 ℃ were also performed. The tensile strength of Ti-45Al-5Nb alloy at 800 ℃ is 765 MPa and the elongation is 16%. Moreover, results of tensile process characteristics and fracture analysis show that this material has two distinct fracture mechanisms at 800 ℃, which are cleavage fracture mechanism and microporous aggregation fracture mechanism. Two fracture mechanisms do not exist at the same time, and for a particular specimen, the fracture process is dominated by only one of them. Different fracture mechanisms are determined by the lamellar orientation difference and element segregation. When the orientation of adjacent grains is similar and the segregation is light, the fracture process is dominated by the cleavage fracture mechanism. Otherwise, proportion and scale of the γ phase at the grain boundary increase and the B2 phase is generated. In this case, the microporous aggregation fracture mechanism will dominate the fracture process.