Aspects of interphase boundary structure in diffusional phase transformations

Distinctions among fully coherent, partly coherent and incoherent interphase boundaries are presented. Introduction of a single linear misfit compensating defect is concluded to represent the most useful definition of the transition between fully and partly coherent interfaces. The limit between partly and fully incoherent interphase boundaries is taken operationally as the absence of detectable misfit accommodating defects (i.e., localization) at the interface by high-resolution transmission electron microscopy. An answer to the question of whether or not a precipitate crystal can be fully or partly coherent at one or more boundary orientations and incoherent at others is developed. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.