Approximants of the icosahedral phase in as-cast Al₆₅Cu₂₀Cr₁₅

Abstract

In A1₆₅Cu₂₀Cr₁₅ four different microstructural components were found after cooling at approximately 100Ks⁻¹ from the melt: (A) Al₁₇Cr₉ with 9 at.% Cu in solution, (B) AlCu with approximately 3 at.% Cr, (C) a face-centred cubic ternary phase with the composition A1₆₅Cu₁₆Cr₁₉ and (D) a region with the composition Al₆₅Cu₂₂Cr₁₃ displaying an inhomogeneous distribution of planar lattice defects and a complex variety of diffraction patterns. By comparison with theoretical diffraction patterns computed by the projection method it is shown that the experimental diffraction patterns obtained from region (D) are due to different approximants of the icosahedral (i) phase ranging from 1/1 (a body-centred cubic phase with a = 1·268 nm) to nearly т (faulted ⇔ phase).