Coupled experimental and computational investigation of omega phase evolution in a high misfit titanium-vanadium alloy

Morphological and compositional evolution of omega (omega) precipitates in a model Titanium-20 wt%Vanadium (or 19 at.%V) alloy has been systematically investigated by coupling transmission electron microscopy and atom probe tomography with atomistic ab initio and continuum microelasticity computations. The initial water quenched microstructure comprised of a fine scale distribution of athermal omega precipitates, which form congruently from the 13 phase via a complete displacive collapse of (222}0 planes, that has been rationalized based on DFT computations. Subsequent annealing at 300 degrees C, over progressively increasing time periods, resulted in isothermal evolution of the omega.) precipitates, whose morphology changes from ellipsoidal to cuboidal, accompanied with V rejection. The highly V-enriched matrix consisted of short V V bond lengths, further distorting the bcc lattice, and increasing the beta/omega misfit. This facilitates the change in the morphology of omega precipitates from ellipsoidal to cuboidal resulting in a (001}(beta) habit plane for these precipitates. The coupled experimental and computational approach permits rationalizing the evolution of w precipitate morphology and composition in such high beta-omega.) misfit beta-Ti alloys. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.