Peritectic solidification of the stable Al−Cu−Co decagonal quasicrystal

X. Z. LIAO*:I:, X. L. MA*:I:, J. Z. JIN*, K. H. KUO*:I: *Department of Materials Engineering, Dalian University of Science and Technology, 116024 Dalian, and ¢Beijing Laboratory of Electron Microscopy, Academia Sinica, PO Box 2724, 100080 Beijing, People's Republic of China Since the first discovery in 1988 of a stable decagonal quasicrystal (DQC) in a slowly solidified A165Cu20- Co15 alloy [1, 2], many papers dealing with its composition range [3, 4], solidification process [4], decaprismatic growth morphology [5-7], stability [8-10], crystal structure [11-13], crystalline approxi- mants [14-17] and anisotropy in physical properties (ten-fold periodic direction versus two-fold quasi- periodic direction) [18-21] have been published. However, information of the solidification process is scarce. Recently, Grushko and Urban [4] studied the peritectic formation of the A1-Cu-Co DQC mainly by scanning electron microscopy (SEM), X-ray diffraction and microanalysis. In this letter we report the results of a transmission electron microscopy (TEM) study on this peritectic solidification process. Both A165Cu20Co15 [1,2] and A165Cu15Co20 [3] alloys are known to yield single DQC after slow solidification. Moreover, Grushko and Urban [4] showed recently that these two alloys correspond to the Cu-rich and the Co-rich compositions of the DQC single-phase region. This was known in 1971 to Skolozdra