The invariant line and precipitation in a Ni-45 wt% Cr alloy

Abstract

A three-dimensional invariant line strain model for f.c.c./b.c.c. phase transformations is developed and used to predict the growth direction and habit plane of lath-shaped precipitates. The results of this approach are shown to be essentially identical to those that can be derived from Bollmann's 0-lattice theory for a Kurdjumov-Sachs orientation relationship. Both theories are in excellent agreement with the experimental observations of Cr-rich (b.c.c.) precipitates in a Ni-Cr alloy. The growth direction of the lath precipitates lies ~5 1 2 ° from the common close-packed directions in the two lattices along an invariant (or near-invariant) line. The observed habit plane, {112} f is the unrolated plane of the phase transformation. The second facet plane of the precipitates, lying close to {313} f, is also predicted from the 0-lattice model.