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

S.J. Qu, A.H. Feng ORCID logo , M.R. Shagiev, H. Xie, B.B. Li, J. Shen show affiliations and emails
Received: 21 November 2018; Revised: 26 November 2018; Accepted: 26 November 2018
Citation: S.J. Qu, A.H. Feng, M.R. Shagiev, H. Xie, B.B. Li, J. Shen. Superplastic behavior of the fine-grained Ti-21Al-18Nb-1Mo-2V-0.3Si intermetallic alloy. Lett. Mater., 2018, 8(4s) 567-571
BibTex   https://doi.org/10.22226/2410-3535-2018-4-567-571

Abstract

The novel Ti-21Al-18Nb-1Mo-2V-0.3Si intermetallic alloy with fine-grained structure exhibited superplastic behavior in the temperature range of 875-1000C with the highest elongation of 958% at 960C. Microstructure analysis revealed that under the optimum superplastic conditions the B2/Alpha2 phase boundary sliding played an important role during superplastic deformation of the Ti2AlNb-based alloy. At 960C, the deformation induced grain growth along with the signs of extensive grain rotation and the O→B2→Alpha2 phase transformations were also observed.Superplastic behavior of the novel Ti-21Al-18Nb-1Mo-2V-0.3Si intermetallic alloy with rather low density of 5.067 g/cm3 was studied. The homogeneous fine-grained microstructure in the alloy, which contained three ordered phases: O (Ti2AlNb), B2 (Ti-Al-Nb) and Alpha2 (Ti3Al), was produced by thermomechanical processing. It included the hot isostatic pressing at 1080C (P=140 MPa for 6 h), two-step quasi-isothermal forging at 870-1060C, and pack rolling at 930-950C. The fine-grained alloy exhibited high superplastic elongations exceeding 230% in the temperature range of 875-1000C and at an initial strain rate of 0.0004 1/s. The maximum elongation of 958% was obtained at 960C. Microstructure analysis revealed that maximum superplastic elongation was obtained when material had approximately equal content of the main B2- and Alpha2-phases suggesting that the B2/Alpha2 phase boundary sliding plays an important role during superplastic deformation. Deviation the Burgers orientation relationships: (110)B2//(0001)Alpha2, [1-1-1]B2//[1-210]Alpha2 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→Alpha2 phase transformations were also observed after testing at 960C. The minor content of the O-phase in the Ti2AlNb-based intermetallic alloy was present at 960C in the (Alpha2+O)-lamellar structure. Crystallographic orientations between the Alpha2- and the O-phases were found to be (1010)Alpha2//(110)O, [0001]Alpha2//[001]O.

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