Microstructure and transformation texture evolution during α precipitation in polycrystalline α/β titanium alloys - A simulation study

A three-dimensional phase field model of beta -> alpha transformation in polycrystalline Ti-6Al-4V (wt.%) alloys is formulated and used to study variant selection and microstructure evolution under different processing conditions and starting beta phase textures. Degrees of variant selection at both individual beta grain and polycrystalline beta volume element levels and their connections to the final micro- and macro-texture of alpha precipitates are analyzed and correlated with the processing parameters. It is found that local stresses in an elastically anisotropic and inhomogeneous polycrystalline volume element lead to obvious variant selection. Under certain pre-strains, a local volume element of a polycrystalline beta sample considered in the simulations could end up with a relatively weak micro- and macro-texture of the transformed alpha phase if it has a strong starting beta phase texture. Moreover, a Fix-End (clamped) boundary constraint to the volume element is found to be more favorable than a Free-End (relaxed) one in preventing the formation of strong transformation texture irrespective of the strength of the starting beta phase texture. Other factors contributing to variant selection and transformation texture development are also discussed. The results could shed light on how to control processing conditions and internal stresses to reduce transformation texture at both the individual beta grain and the polycrystalline volume element level. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.