Effect of cooling rate on transformation texture and variant selection during β → α transformation in Ti-5Ta-1.8Nb alloy

The evolution of texture in a cold rolled Ti-5Ta-1.8Nb alloy sheet, during the alpha -> beta -> alpha transformation has been studied using EBSD and XRD techniques, for different cooling rates. The sheet exhibited a basal plane type texture upon cold rolling, and a sharp '{1 1 -2 0}parallel to rolling plane' transformation texture was inherited after the heat treatment. The microtexture analysis of the lamellar alpha/beta structure, suggested that this transformation texture arises from the {1 1 1}< 1 1 0 > type of high temperature beta texture, obeying the Burgers orientation relationship. The strength of the transformation texture was found to sharply increase with decrease in cooling rates, denoting variant selection. Two types of parent beta orientations with [1 1 0] parallel to either rolling directions are possible, and among their alpha product variants, 3 of them are common, and can be preferentially formed at the prior-beta grain boundaries. The role of grain boundary-alpha in influencing variant selection and the transformation texture for different cooling rates is described in this paper. (C) 2010 Elsevier B.V. All rights reserved.