Roughening transition of decagonal quasi-crystal in undercooled Al72Ni12Co16 alloy

High undercooling of the single-phase decagonal quasi-crystal alloy Al72Ni1 2Co16 was achieved by cyclically superheating the melt in a containerless e lectromagnetic levitation apparatus. The maximum undercooling of the said m aterial was up to 400 K. Transmission electron microscopy (TEM), scanning e lectron microscopy (SEM), and optical microscopy techniques were used to in vestigate the microstructure and identify the phase composition. The decago nal quasi-crystal phase in the samples with small undercoolings showed a fa cet morphology and sew in a lateral growth mode below the roughening transi tion undercooling point, Delta T=64 K. With increasing undercooling, the de cagonal phase assumed an equiaxed structure and indicated a continuous grow th pattern. Toner's surface dynamics model of growing three-dimensional qua si-crystal was adopted to explain the roughening phenomena in the undercool ed melt. (C) 2000 Elsevier Science B.V. All rights reserved.