QUASICRYSTALS, CRYSTALS AND MULTIPLE TWINS IN RAPIDLY SOLIDIFIED Al-Cr-Si, Al-Mn-Si AND Al-Mn-Cr-Si ALLOYS

摘要

The coexistence of quasicrystals and rational approximant structures (RAS) has been observed in melt-spun Al_80Cr_14Si_6, Al_80Mn_14Si_6 and Al_75Mn_10Cr_5Si_10 alloys. The presence of a b.c.c. α-AlMnSi phase in Al-Mn-Si and α-AlMnSi(Cr) phase in Al-Mn-Cr-Si has been seen. A multiple twinning around an irrational axis of the RAS has been reported in an aggregate of fine size cubic crystallites in all three alloys. Selected area diffraction patterns show that the crystalline aggregate symmetry is linked to the icosahedral point group symmetry (m35). Various ways of expressing the twin relationship in the cubic crystalline aggregates have been discussed.