Role of Fe substitution and quenching rate on the formation of various quasicrystalline and related phases

We have investigated Fe substituted versions of the quasicrystalline (qc) a lloy corresponding to Al65Cu20 (CT, Fe)(15) with special reference to the p ossible occurrence of various quasicrystalline and related phases. Based on the explorations of various compositions it has been found that alloy comp ositions Al65Cu20Cr12Fe3 and Al65Cu20Cr9Fe6 exhibit interesting structural phases and features at different quenching rates. At higher quenching rates (wheel speed similar to 25 m/sec) all the alloys exhibit icosahedral phase . For Al65Cu20Cr12Fe3 alloy, however, both the icosahedral and even the dec agonal phases get formed at higher quenching rates, At higher quenching rat e, alloy having Fe 3 at% exhibits two bce phases, bccI (a = 8.9 Angstrom) a nd bccII (n = 15.45 Angstrom), The orientation relationships between icosah edral and crystalline phases are: Mirror plane II [001](bec I) and [351](be c II), 5-fold II [113](bec II) and 3-fold II [110](bec II). At lower quench ing rate, the alloy having Fe 6 at% exhibits orthorhombic phase (n = 23.6 A ngstrom, b = 12.4 Angstrom, c = 20.1 Angstrom). Some prominent orientation relationships of the orthorhombic phase with decagonal phase have also been reported. At lower quenching rate (similar to 10 m/sec), the alloy (Al65Cu 22Cr9Fe6) shows the presence of diffuse scattering of intensities along qua siperiodic direction of the decagonal phase, For making the occurrence of t he sheets of intensities intelligible, a model based on the rotation and sh ift of icosahedra has been put forward.