Design and investigation of high-strength and refined-grained TiAl alloys prepared by the novel low-temperature instantaneous liquid-phases sintering technology

The effects of low-temperature instantaneous In liquid phases on the microstructures and mechanical properties of TiAl alloys have been investigated while a novel dual-stages spark plasma sintering process has been designed to trigger off the sufficient introduction of In liquid phases. The density was enhanced significantly by the introduction of In liquid phases at lower temperatures and pressures, and the maximum reached at 99.48%. Especially, In atoms tended to replace the position of Al atoms in the γ phase to form a substitution solid solution. When the sintering temperature was 1350°C, the (α₂+γ) lamellar colonies with an average size of 402.21 μm were prepared. As the sintering temperature decreased to 1200°C and a pre-sintering process at 700°C was applied, the refined equiaxed γ grains and residual lamellae with an average size of 5.93 μm were obtained. The excessive addition of In elements reduced the density of TiAl alloys and led to In element segregation. Meanwhile, the ultimate tensile strengths (UTS) was enhanced to 635.96 MPa as the In content reached 1.0 at% at room temperature, while the elongation ascended drastically to 76.40% at 900°C. The grains refinement and the the increased density contributed to the ascent of UTS at room temperature, while the rocketed elongations at 900°C were attributed to deformation of refined and equiaxed γ grains during the tensile, which included dislocation activation, localization into slip bands, interaction and rearrangement into walls/networks, and ultimately dislocation dissociation into partials with stacking faults.