Acta Materialia 51 (2003) 4679–4691 www.actamat-journals.com The role of crystallographic and geometrical relationships between a and b phases in an a/b titanium alloy D. Bhattacharyya a , G.B. Viswanathan a,∗ , Robb Denkenberger b , D. Furrer b , Hamish L. Fraser a a The Ohio State University, 477 Watts Hall, 2041 College Road, Columbus, OH, USA b Ladish Co., 5481 S. Packard Ave., Cudahy, WI 53110, USA Received 1 March 2003; received in revised form 25 March 2003; accepted 26 March 2003 Abstract The present study has examined for a/b-Ti alloys the relationship between the morphology and crystallography of Widmansta¨tten plates of a-Ti in colonies within a prior grain of b-Ti. Thus, optical metallography, scanning electron microscopy and transmission electron microscopy have been used to characterize the morphological features of the microstructure, whereas orientation-imaging microscopy (OM) and transmission electron microscopy (TEM) have been employed to reveal crystallographic information. It has been discovered that within a prior b-Ti grain, although the growth direction of the Widmansta¨tten plates in given colonies may differ by large angles from a-plates in other colonies, they may exhibit very close crystallographic relationships. For example, inclined a-plates may share common basal planes and be related by a rotation of ~10.5° about the c-axis of the crystals. This phenomenon has been interpreted on the basis of variant selection of the Burgers orientation relationship commonly adopted between the a and b phases in these alloys. Similar relationships have been observed in a-colonies growing either side of a given prior b grain boundary. These latter observations have been used to draw conclusions concerning the precipitation of a on prior b grain boundaries.  2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: α-β Ti alloys; Burgers OR; Growth directions 1. Introduction Two phase a/b Ti alloys are widely used in the aerospace, energy and bio-medical applications. They are preferred in these applications primarily ∗ Corresponding author. Tel.: +1 614 292 5695; fax: +1 614 292 1537 E-mail address: viswanathan.11@osu.edu (G.B. Viswanathan). 1359-6454/$30.00  2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/S1359-6454(03)00179-4 for the various balances of properties that can be achieved, through heat-treatment, between specific strength, ductility and fracture toughness. The lat- ter property, important for applications where dam- age tolerance is required, is enhanced by the pro- duction of the so-called colony and/or basketweave microstructures, involving the precipitation of Widmansta¨tten plates of a-Ti in b grains. These microstructures are produced by solution heat- treatment in the b-phase field; if the cooling rate