Formation and structure of icosahedral and glassy phases in melt-spun Al-Si-Mn

X-ray scattering and electron-transmission microscopy of melt-spun Al-Si-Mn alloys reveal that the Al-Mn icosahedral phase itself can grow congruently over a range of composition varying from 16 to 20 at.?Mn, and Si atoms substitute Al atoms selectively. The Q dependences of linewidth ΔQ suggest that Hendrick-Teller disorder is dominant; however, the conventional disorders are also present. The glassy Al-Si-Mn alloys show a pronounced prepeak at $Q_p$≊1.6 A${̊}^{\mathrm{-}1}$ and a marked shoulder at the low-Q side of the main peak (Q≊3.0 A${̊}^{\mathrm{-}1}$), suggesting a strong chemical order persisting in the crystalline intermetallic phases.