The role of atomic matching and lattice correspondences in the selection of habit planes

A procedure for predicting precipitate facet planes is demonstrated. The approach is based upon finding interphase boundaries with a high density of near-coincidence sites. Such near-coincidence site boundaries are identified by analyzing computer-generated lattice correspondences. 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 plane of precipitates in Ni-Cr is shown to be a near-coincidence site boundary in which each near-coincidence site lattice cell contains three atoms. This boundary is identified using a non-Pain type of lattice correspondence. However, the observed interfacial structure, growth direction, and facet planes of these precipitates suggest the selection of the habit plane results from geometric matching rather than the existence of a lattice correspondence during the growth process. A lattice correspondence is also proposed that explains the {494} habit plane of martensite in Fe-8Cr-1C. (C) 1997 Acta Metallurgica Inc.