Formation of Surface Layers of Icosahedral Al(Mn)

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Abstract
Surface layers of the icosahedral phase of Al(Mn) have been formed from thin, alternating Al/Mn layers deposited on Al or Fe surfaces by rapid electron-beam or laser melting, by ion beam mixing, and by solid-state diffusion. The electron beam and laser treatments are similar to other liquid quenching techniques used previously to form the phase, but have well defined temperature histories which allow us to place limits on the melting point of the icosahedral phase, the time needed for its nucleation from the melt, and its growth velocity. Ion beam mixing is a way of forming the icosahedral phase which is quite different from melt quenching; the phase is formed during ion beam mixing at temperatures of 100–200°C. For mixing at ≤60C an amorphous phase with icosahedral short-range order is formed; this phase can be converted to the icosahedral phase by subsequent annealing. Formation of the icosahedral phase by reacting the as-deposited layers in the solid state is a new technique not previously reported. The results presented here place new restrictions on proposed structural and thermodynamic models for the icosahedral phase.