The microstructure of rapidly solidified Al−Mn alloys containing 18 to 25.3 wt pct Mn was studied by transmission electron microscopy. One of the phases found in the microstructure exhibits icosahedral symmetry manifested in electron diffraction patterns having five-fold symmetry. A new structural concept is proposed to account for the observed electron diffraction patterns. The structure is assumed to be composed of many connected polyhedra. Although not forming a regular lattice, such structures are able to produce sharp diffraction peaks. The terminal stability and transformation of the icosahedral phase was also studied and reported.

The microstructure of rapidly solidified Al 6 Mn

We express the cubic (Al, Zn)49Mg32 structure as a periodic packing of the rhombohedra1 cells from the three-dimensional Penrose tiling, decorated by atoms. This decoration is extended to the aperiodic quasicrystal packing of the same cells to give a hypothetical structure for the recently discovered icosahedral phase with the same composition. This is the first structure of a real system which is related both to quasicrystals and to Frank-Kasper icosahedral close packings.

A. D. I. Nicol

Papers

The structure of MnAl6