Quasicrystalline Phase transformation in the quaternary and ternary systems AlCuMnFe and AlPdMn

摘要

An unified structural model has been devised [1] that describes both icosahedral phases i-AlPdMn and i-AlCuFe. The model suggests that possible icosahedral structures could be found in alloys with general composition Al_(61.8)(Pd|Cu)_(21.35) (Mn|Fe)_(8.29)(Al|Fe|Mn)_(4.28)(Al|Cu)_(4.28). Applied to the systems AlCuMnFe [2] and AlPdFe [3], this formula leads to the compositions Al_(66.08)Cu_(21.35)Mn_(8.29)Fe_(4.28) and Al_(70.36)Pd_(21.35)Fe_(8.29) that have both been synthetized by rapid quenching and annealing. The as-quenched quaternary alloy Al_(66.08)Cu_(21.35)Mn_(8.29)Fe_(4.28) exhibits a F-icosahedral phase that transforms into a decagonal phase after annealing. Its 10-fold axis aligns along one of the 5-fold axes of the icosahedral phase. This implies a group-subgroup transformation, with the kernel group 5m, analogous to the one observed during CFC to HCP transformations, with kernel 3m. The as-quenched and annealed ternary alloy Al_(70.36)Pd_(21.35)Fe_(8.29) is similar to i-AlPdMn with an iso-morphic substitution of Mn with Fe. A study of the phase diagram of the system AlPdFe [3] shows that the results are compatible with the structural model proposed here in strong relations with those presented in [1] for i-AlPdMn.