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

A variation in the structure of the decagonal phase with composition and phase transformations related to the decagonal phase have been observed in Al₇₀Ni_30-xCo_xalloys with x varying from 16 to 24. A decagonal phase with fundamental reflections at Al₇₀Ni₂₄Co₆converts to a (type I) superstructure around Al₇₀Ni₁₈Co₁₂and to another type (II) of superstructure at Al₇₀Ni₁₄Co₁₆An 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.