Icosahedral particles of Al-Mn alloy produced by gas evaporation.

Small particles of icosahedral Al-Mn alloy have been produced by evaporation of Al and Mn metals in Ar gas, and studied by electron microscopy. The quasicrystalline particles were sphere in shape, with diameter ranging from 500 to 3000angstroms, and showed speckled contrast in bright field images, characteristic of strain. Dark field images revealed granular bright and dark areas of a few hundred angstroms. This appearance is common with the melt-spun samples, and may be attributed to misorientations between the granular domains. Elongated domains of ~ 50angstroms in width and a few hundred angstroms in length, which is unique in the present sample, and not observed in the melt-spun sample, were also found. The critical cooling rate for the quasicrystal formation of Al-Mn alloy was found to be 10 sup 5 C/s.