Coherent orientation relationship among various quasicrystalline and crystalline phases in rapidly solidified Al78Mn20Ge2 alloy

Abstract

Rapidly solidified Al78Mn20Ge2 alloy exhibits a curious structural feature; this corresponds to the simultaneous occurrence of almost all the quasicrystalline phases, e.g., primitive and face-centered icosahedral phase, rational approximant, and a new metastable cubic phase. The cubic crystalline phase shows yet another type of recently observed twin relation which effectively produces an icosahedral symmetry, a feature that has so far been specific to alloy systems Al-Mn-Si and Al-Mn-Fe-Si only. The diffraction evidences obtained in the present investigation reveal that the orientation of the structural subunit, which is a MacKay icosahedron, remains invariant across the various interphase boundaries. These results elucidate clearly the structural interrelationship among the various phases.