Orthorhombic crystalline approximants of the Al-Mn-Cu decagonal quasicrystal

Abstract

Two orthorhombic Al–Mn–Cu phases, π-Al₂₀Mn₃Cu₂ and Y-AlMnCu, with large lattice parameters were found to coexist with the decagonal quasicrystal in Al₁₀Mn₃Cu_0.1-0.2 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 π phase is a layer of the π phase and vice versa. Therefore, these two phases intergrow frequently and both translational and rotational twin domains are abundant.