Part II crystallography and morphology of the β → ζ massive transformation in Ag-26 a/ o Al

Abstract

Orientation relationships between parent β grains and grain face- or edge-nucleated ζ m crystals have been determined for the β → ζ m massive transformation in Ag-26 a/o Al, principally by means of selected area electron channelling, but supported by selected area electron diffraction. For 46 of 47 ζ m crystals analyzed a Burgers orientation relationship obtains exactly or nearly so with at least one of the parent grains forming the grain boundary at which nucleation occurred. Approximately half of the orientation relationships between ζ m and the non-Burgers related β grains can be expressed in terms of parallel planes and directions with relatively low indices. An O-lattice-based analysis of these nonBurgers orientation relationships indicates that somewhat more than half of them correspond to partially coherent interphase boundaries. However, the observation that β: ζ m interfaces between non-Burgers-as well as between Burgers-related ζ m and β grains are heavily faceted suggests that a much larger proportion of these boundaries has a partially coherent interfacial structure than either the orientation relationship data or the analyses of this data indicate. The observations that ζ m crystals with similar shape formed along a β grain face of approximately constant orientation have the same spatial orientation to within ±1° and that primary ζ m sideplates developed at a small-angle β grain boundary provide further support for the ubiquity of low energy orientation relationships between ζ m and β and for the similarity between the massive and precipitation reactions in all aspects other than that of a composition difference between product and matrix phases.