Models and observations of fcc/bcc interfaces

Abstract

SUMMARY Whereas models of the structure and periodicity of CSL or near CSL high angle grain boundaries are relatively well developed and have been to some extent verified by experiment, the nature of more general (e.g. fcc/bcc) interfaces is very imperfectly understood. One of the major differences between homo‐ and heterophase boundaries is the occurrence, in the latter case, of reproducible orientation relationships due to the crystallographic requirements of phase transformation (e.g. a glissile interface for martensitic growth, low energy interfaces for classical nucleation). A review is given of the relationships commonly observed to obtain between fcc and bcc crystals (as well as ordered phases based upon these structures). Within a given relationship, it is possible to use models of the available interfaces to predict their dislocation content; the success of the various approaches is considered. It is shown that the dislocation arrays identified on fcc/bcc boundaries are consistent with the occurrence of a primary structural relaxation, but that the latter does not appear to be complete. Possible reasons for this are discussed, together with the extent to which secondary structural models may be applicable. Attempts to rationalize the observed orientation relationships and morphologies are discussed, and it is pointed out that these all rely on searches for situations of minimum primary misfit, but that the way in which the latter is quantified determines the results of the analyses. Nevertheless, the implication is that the primary misfit does appear to determine the actual behaviour, though no structural or mechanistic conclusions can safely be drawn from this observation.

Phason—Phonon-assisted epitaxy at icosahedral—decagonal interfaces in Al—Pd—Mn quasicrystals

“…see review articles by Ecob (1985) and Aaronson et al (1990)). Geometrical theories such as the O-lattice model (Bollmann 1967) or crystallographic invariance line determination (Dahmen 1982) are generally associated with energetic considerations in order to interpret why interface structures are coherent, semicoherent (with interfacial dislocation lattices) or incoherent (with interfacial ledge structures).…”

“…Both decagonal and icosahedral Al-Pd-Mn phases are actually known to be perfect quasicrystals and their interfaces can be perfectly planar and structurally coherent. This may facilitate the analyses of high-resolution electron microscopy (HREM) images and their understanding in terms of phason and phonon strains on the basis of published models (Lubensky et al 1986, Ishii 1989, Qiu and Jaric 1989. This is going to be demonstrated further in the forthcoming sections of the paper.…”

“…1986, Ishii 1989, Qiu and Jaric 1989, the AQ /I shifts may be analysed in term of a simple first-order linear phason and phonon strain field, such as AQ 11 = 8 /l'Qi, +-l//lQ lo.…”

Improved determination of fcc/bcc orientation relationships by use of high‐indexed pole figures

“…An overview of the various models is given e.g. in [20][21][22]. Until recently a similar semi-automatic reconstruction of bcc/fcc materials is desirable although manual analysis appears to be possible [11,15].…”