TRANSMISSION ELECTRON-MICROSCOPY STUDY OF DEFECTS IN A DIRECTIONALLY GROWN AL-CU-CO-GE SINGLE QUASI-CRYSTAL

Large single decagonal quasicrystals of Al-Cu-Co-Ge alloy about 0.8 mm in diameter and 10 mm in length have been obtained by the directional growth technique. The single decagonal quasicrystals show decaprismat ic morphology and their perfection was examined by electron diffractio n. It was found that the perfection of these single quasicrystals depe nds on the growth rate during the directional solidification. A high d ensity of mixed dislocations with Burgers vectors b parallel to the te nfold axis and stacking faults with displacement vectors R parallel to the tenfold axis were introduced into the quasicrystals during rapid directional growth. The effects of the temperature gradient and rate o f growth on the defect formation during directional growth are discuss ed.