Diffusion of 57Co in decagonal Al–Ni–Co-quasicrystals

Self-diffusion of 57Co in decagonal Al–Ni–Co single quasicrystals was studied for both principal directions as a function of the temperature by means of the radiotracer method. In combination with serial sectioning, diffusivities were measured over a large temperature range from 732 to 1273 K. Below about 1120 K diffusion is described by an Arrhenius behaviour along both the periodic and the quasiperiodic directions. The magnitude of the activation enthalpies and pre-exponential factors support a vacancy-type diffusion mechanism. A small anisotropy of diffusion which is temperature-dependent but never exceeds 30% was detected. Above 1120 K, a kink in the Arrhenius curve is observed. We attribute this behaviour to a phase transition from the decagonal basic Co-rich phase to an ordered modification.