Interface Between Simple Crystal and Icosahedral-Symmetry Related Crystal

Abstract
The phase diagram of transition metal intermetallics exhibits a systematic sequence of phases involving simple crystals and complex crystal structures with icosahedral motifs (β-W, σ, X phases). Such intermetallic alloys provide then convenient examples to establish basis for the analysis of simple crystal/ icosahedral phase interfaces. The σ and X intermetallic phases in a Fe-Cr-Mo steel have been studied by Transmission Electron Microscopy : the interface as well as the orientation relationships has been identified. A simple geometrical analysis is proposed to account for the ferrite/σ-phase interface, σ/X orientation relationship and X-phase antiphase boundaries. This approach emphasizes on the necessity to consider corrugated compact layers instead of lattice planes in icosahedral phases and the conservation of the site density at the interface plane.