Abstract
ABSTRACTAb initio calculations were carried out to compare the mechanical properties of β-based non-canonical Al–Cu–Fe approximants of quasicrystals with cubic (β), monoclinic (η) and orthorhombic (ξ1, ξ2) structures, which all demonstrate high strengthening. The aim was to elucidate the competitive effects of the η- and ξ-ordering and iron content on deformation behaviour of these phases. We found that the Young’s modulus, polycrystalline shear modulus, mechanical stability and shear elastic modulus G(n,m) for different slip planes decrease for β-Al50Cu1-xFex with lowering iron content, but they grow from β-Al50Cu31.25Fe18.75 to the ordered η-Al50Cu45Fe5, and ξ2-Al45.5Cu50Fe4.5 that indicates a growing resistance to plastic deformation due to ordering and agrees well with our experimental finding. The preferable slip systems were predicted based on the calculated generalised stacking fault (GSF) energies in β-(Cu,Fe)Al and η-(Cu,Fe)Al with similar Fe concentration. The GSF energies confirmed also that the strengthening observed in η-phase is related to ordering rather than the Fe effect in consistence with a stronger covalent bonding in η-phase.
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