Improvement on high-temperature tensile strength and ductility of selective electron beam melting TiAl alloys via small-strain forging

Abstract

In the present work, a Ti–48Al–2Cr–2Nb alloy prepared by selective electron beam melting (SEBM) and post-treated by forging at a small strain was investigated. The results show that the microstructure of the as-built TiAl alloys exhibited an alternating layer of coarse single γ grains and fine γ+α2 grains configuration along the building direction. After forging at a small strain, the fraction of the coarsely grained region decreases, and substantial fine sub-grains form in the fine-grained region. Additionally, fractions of the α2 phase and α2/γ lamellar colonies increase. These factors lead to an increase in the tensile strength of alloys. Meanwhile, the low-angle grain boundaries (LAGBs) in fine sub-grains and the substantial mobile dislocations in coarse γ grains are favorable for improving the ductility of alloys. The formation of deformation twins in the γ grains facilitates the simultaneous improvement of strength and ductility. In addition, the anisotropy of tensile properties is reduced after small-strain forging, which can be attributed to the reduction in fraction of the coarse γ grains, and the increase in the fractions of the α2 phase and α2/γ lamellar structure. Therefore, small-strain forging was verified as an effective post-treatment method for the improvement of tensile strength and ductility of SEBM prepared TiAl alloys at high temperatures.