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Achieving Bi-Lamellar Microstructure with Both High Tensile Strength and Large Ductility in Ti-6Al-4V Alloy by Novel Thermomechanical Processing

34 Pages Posted: 15 Aug 2019 Publication Status: Accepted

See all articles by Yan Chong

Yan Chong

Kyoto University - Department of Materials Science and Engineering; University of California, Berkeley - Department of Materials Science and Engineering

Tilak Bhattacharjee

Kyoto University - Department of Materials Science and Engineering; National Institute for Materials Science - Elements Strategy Initiative for Structural Materials (ESISM)

Jangho Yi

Kyoto University - Department of Materials Science and Engineering

Shiteng Zhao

Kyoto University - Department of Materials Science and Engineering; University of California, Berkeley - Department of Materials Science and Engineering

Nobuhiro Tsuji

Kyoto University - Department of Materials Science and Engineering

Abstract

In this study, a novel through-β-transus processing followed by intercritical annealing was designed to obtain the bi-lamellar microstructure in Ti-6Al-4V alloy with refined colony sizes, by which both tensile strength and ductility were significantly improved. The colony size obtained in the through-β-transus processing was 60 μm, much smaller than the minimum colony size of 130 μm that can be achieved in the conventional β processing. The colony refinement was attributed to the decreased size of the grain boundary α phase with increased variety of crystallographic orientations, which acted as nucleation sites for subsequent colony structures. By intercritical annealing of the lamellar microstructures in α+β two-phase region followed by water quenching, bi-lamellar microstructures composed of primary α lamellae and transformed β regions composed of fine secondary α plates were obtained, maintaining the same colony size as the lamellar precursors. The total elongation of bi-lamellar microstructure significantly improved from 3.4% to 18.6% with decreasing the colony size, while the high yield and tensile strength was independent of the colony size. SEM-EBSD characterization of the bi-lamellar microstructures at interrupted tensile strains clarified that deformation behaviors of the bi-lamellar microstructures after yielding were mainly controlled by micro-shear bands across transformed β regions, which eventually evolved into micro-cracks at higher tensile strains. It was considered that the strain compatibility accommodated by the differently aligned micro-shear bands formed within different colonies was the main reason for delaying tensile fracture in the bi-lamellar microstructure with the smaller colony size.

Keywords: Ti-6Al-4V, Lamellar, Bi-Lamellar, Colony Size, Micro-Shear Bands

Suggested Citation

Chong, Yan and Bhattacharjee, Tilak and Yi, Jangho and Zhao, Shiteng and Tsuji, Nobuhiro, Achieving Bi-Lamellar Microstructure with Both High Tensile Strength and Large Ductility in Ti-6Al-4V Alloy by Novel Thermomechanical Processing (August 13, 2019). Available at SSRN: https://ssrn.com/abstract=3436426 or http://dx.doi.org/10.2139/ssrn.3436426

Yan Chong (Contact Author)

Kyoto University - Department of Materials Science and Engineering ( email )

Japan

University of California, Berkeley - Department of Materials Science and Engineering ( email )

Berkeley, CA
United States

Tilak Bhattacharjee

Kyoto University - Department of Materials Science and Engineering

Yoshida-Honmachi
Sakyo-ku
Kyoto, 606-8501
Japan

National Institute for Materials Science - Elements Strategy Initiative for Structural Materials (ESISM)

Japan

Jangho Yi

Kyoto University - Department of Materials Science and Engineering

Japan

Shiteng Zhao

Kyoto University - Department of Materials Science and Engineering

Japan

University of California, Berkeley - Department of Materials Science and Engineering

Berkeley, CA
United States

Nobuhiro Tsuji

Kyoto University - Department of Materials Science and Engineering ( email )

Yoshida-Honmachi
Sakyo-ku
Kyoto, Kyoto 606-8501
Japan

HOME PAGE: http://www.tsujilab.mtl.kyoto-u.ac.jp

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