Materials Transactions Online

Materials Transactions, Vol.55 No.05 (2014) pp.763-767
© 2014 The Japan Institute of Metals and Materials

Aging Effect on Microstructure of Cold Groove-Rolled α′-Type Ti-12 mass%V-2 mass%Al Alloys Studied by Transmission Electron Microscopy

Kazuhisa Sato, Hiroaki Matsumoto, Akihiko Chiba and Toyohiko J. Konno

Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

Microstructure and phase decomposition of hexagonal α′ martensite in cold groove rolled (CGR) Ti-12 mass%V-2 mass%Al alloys have been studied by transmission electron microscopy and electron diffraction. Acicular structure of the α′ martensite changes into equiaxed α′ grains by CGR with a cold reduction of 75%. After aging at 573 K for 500 h, local Moiré fringes disappear and diffraction rings become sharp due to recovery. However, Vickers hardness also increased in spite of the recovery. Partitioning of solute atoms and/or formation of fine precipitates can be possible cause for the observed age-hardening. Although a CGR alloy is characterized by a microstructure with polycrystalline equiaxed grains, following orientation relationship is locally observed between β precipitates and α grains after aging at 673 K: (101)β // (011 1)α, [010]β // [1011]α. Electron tomography revealed a heterogeneous nucleation and growth of β precipitates in the deformed α′ matrix.

(Received 2013/12/26; Accepted 2014/02/20; Published 2014/04/25)

Keywords: α′-martensite, titanium-vanadium-aluminum, cold groove rolling, recovery, transmission electron microscopy (TEM), electron tomography

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