THE ROLE OF ATOMIC MATCHING AND LATTICE CORRESPONDENCES IN THE SELECTION OF HABIT PLANES

A procedure for predicting precipitate facet planes is demonstrated. T he approach is based upon finding interphase boundaries with a high de nsity of near-coincidence sites. Such near-coincidence site boundaries are identified by analyzing computer-generated lattice correspondence s. For f.c.c./b.c.c. transformations, numerous lattice correspondences yield a similar degree of matching in 3-dimensions but substantially different matching in two-dimensions. The (1(2) over bar1$)(f) habit p lane of precipitates in Ni-Cr is shown to be a near-coincidence site b oundary in which each near-coincidence site lattice cell contains thre e atoms. This boundary is identified using a non-Pain type of lattice correspondence. However, the observed interfacial structure, growth di rection, and facet planes of these precipitates suggest the selection of the habit plane results from geometric matching rather than the exi stence of a lattice correspondence during the growth process. A lattic e correspondence is also proposed that explains the {494} habit plane of martensite in Fe-8Cr-1C. (C) 1997 Acta Metallurgica Inc.