A TEM study of the crystallography and interphase boundary structure of α precipitates in a Zr-2.5 wt% Nb alloy

Abstract

The crystallography and the interfacial structure of α precipitates (h.c.p.) and β matrix (b.c.c.) boundaries in a Zr-2.5wt% Nb alloy have been studied using TEM. The orientation relationship was found to deviate slightly from the ideal Burgers orientation relationship. The habit plane of precipitates has been determined, and found to be normal to some particular Δ gs. The habit plane is characterized by a single set of misfit dislocations, about 10 nm apart, parallel to the long axis of the α plate. The Burgers vector of these dislocations, as determined by g·b contrast analysis, is [0 1 0] with respect to β phase. The experimental observations are discussed in terms of an invariant line strain and the condition of optimal atomic matching in the habit plane as proposed in a recently-developed model. The observations tend to support the predictions of the model.