ORTHORHOMBIC CRYSTALLINE APPROXIMANTS OF THE AL-MN-CU DECAGONAL QUASI-CRYSTAL

Two orthorhombic Al-Mn-Cu phases, pi-Al20Mn3Cu2 and Y-AlMnCu, with large lattice parameters were found to coexist with the decagonal quasicrystal in Al10Mn3Cu0.1-0.2 alloys and they were shown to be crystalline approximants of the latter. These two phases have similar structural subunits and a close orientation relationship. They twin easily and the twin boundary of the pi-phase is a layer of the Y phase and vice versa. Therefore, these two phases intergrow frequently and both translational and rotational twin domains are abundant.