TRANSMISSION ELECTRON-MICROSCOPIC INVESTIGATIONS OF RAPIDLY SOLIDIFIED AL-MN-NI QUASI-CRYSTALLINE ALLOYS

The formation of quasicrystalline phases in rapidly solidified Al-Mn-Ni alloys (Al60Mn11Ni4 and Al80Mn13Ni7) has been investigated by X-ray diffraction and TEM techniques. X-ray diffraction studies indicate that the icosahedral phase preferentially nucleates on the side of the ribbon that is in contact with the copper wheel during melt spinning. As indicated by the width (f.w.h.m.) of the XRD peaks, the substitution of Ni in Al-Mn results in the formation of more ordered quasicrystalline phases. Microstructural and electron diffraction (SAD and CBED) investigations show the simultaneous occurrence of icosahedral and decagonal phases. The present investigation reveals the epitaxial-like growth mode of the decagonal phase on the icosahedral phase. For example, it has been found that a pseudo-fivefold axis of the decagonal phase grows parallel to fivefold axis of the icosahedral phase. Other orientational relationships have also been studied. The occurrence of five-times modulation along a tenfold axis in the decagonal phase is also reported.