Structural variation and phase transformations of decagonal quasicrystals in the Al-Ni-Co system

Abstract

A variation in the structure of the decagonal phase with composition and phase transformations related to the decagonal phase have been observed in Al70Ni30-xCox alloys with x varying from 16 to 24. A decagonal phase with fundamental reflections at Al70Ni24Co6 converts to a (type I) superstructure around Al70Ni18Co12 and to another type (II) of superstructure at Al70Ni14Co16 . An order-disorder transformation in the type-I superstructure of the decagonal quasicrystal has been observed in alloys with x varying from 12 to 15 in the temperature range from 973 to 1073 K. The other transformation from a mixture of a decagonal phase and a cubic Al(Ni, Co) phase to crystalline phases has been identified in the alloys with x varying from 18 to 20 in the temperature range between 1273 and 1073 K. Both transformations are reversible.