The role of crystallographic and geometrical relationships between α and β phases in an α/β titanium alloy

The present study has examined for alpha/beta-Ti alloys the relationship between the morphology and crystallography of Widmanstatten plates of alpha-Ti in colonies within a prior grain of beta-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 beta-Ti grain, although the growth direction of the Widmanstatten plates in given colonies may differ by large angles from alpha-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 similar to10.5degrees 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 alpha and beta phases in these alloys. Similar relationships have been observed in alpha-colonies growing either side of a given prior beta grain boundary. These latter observations have been used to draw conclusions concerning the precipitation of alpha on prior beta grain boundaries. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.