Diffusion in quasicrystalline Al–Ni–Co and Al–Pd–Mn

Abstract

Diffusion coefficients of 60Co in single decagonal (d-)Al72.2Ni11.8Co16.0 quasicrystals and of 63Ni in single icosahedral (i-)Al70Pd21Mn9 were measured by the radioactive tracer method. The volume diffusion coefficients can be described by an Arrhenius equation.Anisotropic diffusion behaviour was observed in the d-Al–Ni–Co quasicrystals, in which the mobility of Co is slightly faster along the periodic direction. The activation enthalpies for Co diffusion in d-Al–Ni–Co are Q=277.4kJmol−1 (periodic direction), Q=289.0kJmol−1 (aperiodic direction) and for Ni diffusion in i-Al–Pd–Mn Q=209.0kJmol−1. The results are discussed together with data of similar diffusion investigations in icosahedral quasicrystals, and a diffusion mechanism via vacancies is suggested. In addition, we have determined surface self-diffusion coefficients of 60Co in the d-Al–Ni–Co quasicrystalline alloy and have obtained different activation energies of surface diffusion for the periodic (Q=147kJmol−1) and the quasiperiodic direction (Q=137kJmol−1).