Simultaneous enhancements of strength and ductility of additively manufactured Ti-6.9Al-6.8Zr-2.3Mo-2.2V alloy by cyclic heat treatment and solution-aging

Abstract

In the paper, in terms of the new developed additively manufactured Ti-6.9Al-6.8Zr-2.3Mo-2.2V alloy, different microstructural design strategies were proposed to tune the morphology and content of α phase to optimize the mechanical properties of the alloy and the corresponding deformation mechanism of the alloy were characterized and analyzed. The results show that after cyclic heat treatment and solution-aging, the best comprehensive mechanical properties (yield strength ∼ l009 MPa, and elongation ∼12%) are obtained. The better comprehensive tensile properties are attributable to the microstructure consisting 16% equiaxed αp and βt structure. The cycle heat treatment can effectively decrease the length-width ratio of lamellar α phase and improve spheroidization of primary α phase. The equiaxed primary α phase has higher ability to coordinate local plastic strain, leading to the activation of extensive prismatic <a> slip and improving the ductility of the alloy. After aging-solution, large amount of fine αs precipitate from β phase. The high hetero-deformation induced stress at αs/β interfaces in βt structure promotes the activation of the pyramidal <a> slip systems, thereby increasing the yield strength. The present findings provide significant guidance for additive manufactured titanium alloy having good combination of tensile ductility and strength.