Superimposed patterns and projections (for martensite transformations etc.)

Abstract

In addition to the appearance of extra spots due to twinning etc., patterns are also obtained from specimens in which two phases with some particular mutual orientation relationship are present. One phase may have formed directly from the other by a martensitic type of transformation or the pattern may be from a precipitate and matrix. The case where a close-packed hexagonal phase can form from a face-centred cubic phase is closely connected with twinning (and stacking fault formation) in the latter. The corresponding positions of diffraction spots for face-centred cubic twin planes {111} and hexagonal (00.1) normal to the diffraction pattern have already been shown in Figs. 37 and 38. It is useful to consider what kinds of diffraction pattern can be formed when the two cubic phases, i.e. face-centred or body-centred, are present together or, alternatively, when either or both occur with the hexagonal phase.