Effect of heat treatment on the microstructure and anisotropy of tensile properties of TiAl alloy produced via selective electron beam melting

Abstract

Selective electron beam melting (SEBM) is considered to be a promising method to fabricate TiAl alloy components with complex geometries. In this work, the effect of annealing on the microstructure and anisotropy of tensile properties of SEBM-produced Ti–47Al–2Cr–2Nb alloys was systematically investigated. The results indicated that the SEBM-produced TiAl alloy samples exhibited equiaxed and elongated grains in the transverse and longitudinal directions, respectively, and presented anisotropy of the tensile properties. For the sample produced at an energy density of 24.07 J/mm3, the microstructure in the vertical cross section presented an elongated lamellar structure consisting of (α2/γ) lamellar colonies, after annealing at 1310 °C for 3 h; on the other hand, for the same sample, elongated grains were almost invisible after annealing at 1370 °C for 2 h. Further, for the sample produced at an energy density of 35 J/mm3, the elongated grains remained after annealing at 1370 °C for 2 h and were destroyed by cyclic heat treatment. The texture intensity and anisotropy of the tensile properties of the two samples fabricated with different processing parameters were weakened by annealing at 1370 °C for a duration of 2 h and cyclic heat treatment between the α+β+γ and α phase regions, respectively. Both the tensile strength and elongation increased as a result of heat treatment. Moreover, the phase transformation during annealing was analyzed.