Czochralski growth and characterization of large decagonal Al-Co-Ni quasicrystals

In the ternary Al-Co Ni system, decagonal quasicrystals occur that are ther modynamically stable and can be grown using rather conventional crystal gro wth techniques at near-equilibrium conditions. Derailed studies of the Al-r ich part of the ternary phase diagram including the primary crystallization field of the decagonal phase are known from the literature. Using these da ta quasicrystal growth by the Czochralski method from off-stoichiometric (A l-rich) melts has proved to be successful. In a series of growth experiment s with varying Co:Ni ratio along the 1050 and 1100 degreesC isotherms, sing le-grain quasicrystals up to 1 cm(3) in size have been grown. Use was made of very low growth rates (0.2-0.5 mm/h) as to meet the needs of the constit utional supercooling criterion as well as those arising from the anisotropi c growth kinetics of the decagonal phase. The segregation behaviour was stu died by electron probe microanalysis (EPMA) measurements concerning the cha nge in the Al concentration during growth and the shift in the Co:Ni ratio which marks the main extension of the decagonal stability region. (C) 2000 Elsevier Science B.V. All rights reserved.