Nucleation and variant selection of secondary α plates in a β Ti alloy

The microtexture of secondary alpha plates in Ti-4.5Fe-6.8Mo-1.5A1 has been investigated by electron backscatter diffraction (EBSD) to obtain more insight in the nucleation and variant selection of these a plates. A statistical analysis of the EBSD data shows that for most P grain boundaries the variant selection of the alpha plates is in agreement with a commonly used variant selection criterion yielding that the alpha-{0001} pole is nearly parallel to the closest beta-{110} poles of the two adjacent beta grains. For a small angle between the beta-{110} poles nucleation is predominantly observed at both sides of the grain boundary, while with increasing angle some beta grain boundaries exhibit nucleation of alpha plates at only one side. In the beta grain interior many so-called Type 2 alpha-alpha grain boundaries are observed which are thought to originate from autocatalytic nucleation when a new alpha plate is formed at an existing alpha-beta interface. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.