Superplastic behavior of the fine-grained Ti-21Al-18Nb-1Mo-2V-0.3Si intermetallic alloy

Abstract

Superplastic behavior of the novel Ti-21Al-18Nb-1Mo-2V-0.3Si intermetallic alloy with rather low density ρ ≈ 5.067 g / cm 3 was studied. The homogeneous fine-grained microstructure in the alloy, which contained three ordered phases: O (Ti 2 AlNb), B2 (Ti-Al-Nb) and α 2 (Ti 3 Al), was produced by thermomechanical processing. It included the hot isostatic pressing at 1080°C (P = 140 MPa for 6 h), two-step quasi-isothermal forging at 870 -1060°C, and pack rolling at 930 -950°C. The fine-grained alloy exhibited high superplastic elongations δ > 230 % in the temperature range of 875 -1000°C and at an initial strain rate of 4 × 10 −4 s −1 . The maximum elongation δ = 958 % was obtained at 960°C. Microstructure analysis revealed that maximum superplastic elongation was obtained when material had approximately equal content of the main B2-and α 2 -phases suggesting that the B2 / α 2 phase boundary sliding plays an important role during superplastic deformation. Deviation the Burgers orientation relationships: (110) B2 // (0001) α2 , [1-1-1] B2 // [1-210] α2 pointed out to extensive grain rotation during superplastic flow. The deformation induced grain growth testified to grain boundary migration. Besides, the signs of the O→B2→α 2 phase transformations were also observed after testing at 960°C. The minor content of the O-phase in the Ti 2 AlNb-based intermetallic alloy was present at 960°C in the (α 2 + O)-lamellar structure. Crystallographic orientations between the α 2 -and the O-phases were found to be (1010) α2 // (110) O , [0001] α2 // [001] O .

Optimizing the Integrity of Linear Friction Welded Ti2AlNb Alloys

“…The Ti 2 AlNb-based alloys have been developed by the addition of niobium to Ti 3 Albased intermetallic alloys [1][2][3][4]. As the ordered orthorhombic Ti 2 AlNb phase (O phase) can inhibit dislocation motion and crack propagation [5,6], Ti 2 AlNb-based alloys possess higher specific strength, fracture toughness, creep resistance at 650~750 • C [7,8], and especially better processability than Ti 3 Al-based alloys [9]. These advantages have made Ti 2 AlNbbased alloys become one of the most potential lightweight high-temperature structural materials for aero-engines [10,11].…”