Thermal stability of the icosahedral phase in AlMn (Mn=4−15 at.%) alloys prepared by planar flow casting

A series of AlMn ribbons were prepared by planar flow casting in the range of compositions between 4 and 15 at.% Mn. Their thermal stability was investigated by X-ray diffraction, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). X-ray diffraction measurements on the as-quenched ribbons showed the presence of a supersaturated Al (Mn) solid solution and the icosahedral phase. The morphology depends on the composition and on the local quenching rate. Several exothermic effects (at least two) were observed on the DSC curves. The temperature and intensity of these effects varied when the manganese content was changed.

Identification of the individual stages along the DSC curve was carefully followed by stopping the DSC experiment at various points during the exothermic evolution, rapidly cooling the specimen and carrying out the X-ray diffraction measurements and the observations by TEM on the same specimen. It is shown that the thermal stability of the icosahedral phase is greatly influenced by its initial morphology.