Abstract
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 // (01−1−1)α , [010]β // [10−11]α . Electron tomography revealed a heterogeneous nucleation and growth of β precipitates in the deformed α′ matrix.
