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

Diffusion coefficients of Co-60 in single decagonal (d-)Al72.2Ni11.8Co16.0 quasicrystals and of Ni-63 in single icosahedral (i-)Al70Pd21Mn9 were measu red 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 quasicrystal s, in which the mobility of Co is slightly faster along the periodic direct ion. The activation enthalpies for Co diffusion in d-Al-Ni-Co are Q=277.4 k J mol(-1) (periodic direction), Q=289.0 kJ mol(-1) (aperiodic direction) an d for Ni diffusion in i-Al-Pd-Mn Q=209.0 kJ mol(-1). The results are discus sed together with data of similar diffusion investigations in icosahedral q uasicrystals, and a diffusion mechanism via vacancies is suggested. In addi tion, we have determined surface self-diffusion coefficients of Co-60 in th e d-Al-Ni-Co quasicrystalline alloy and have obtained different activation energies of surface diffusion for the periodic (Q=147 kJ mol(-1)) and the q uasiperiodic direction (Q=137 kJ mol(-1)). (C) 2000 Elsevier Science B.V. A ll rights reserved.