Solute diffusion of Ni in icosahedral Al-Pd-Mn quasicrystals

This paper presents the results of an experimental study of Ni solute diffusion in the single-grain icosahedral quasicrystalline compound Al 70 Pd 21 Mn 9 . Ni solute diffusion coefficients were measured over a temperature range from 699 to 1074 K. The radiotracer technique in combination with serial sectioning of the diffusion samples was used to determine concentration depth profiles. No deviation from Arrhenius behaviour was detected in the temperature range covered by the present experiments. The results are compared with the available diffusion data on quasicrystals and on diffusion in Al and various diffusion mechanisms proposed for quasicrystals are discussed. The most striking fact is that the diffusion of Ni and the diffusion of other transition-metal elements are found to be much slower than diffusion of non-transition-metal elements such as Ge and Zn in i-(Al-Pd-Mn) quasicrystalline alloys. Moreover, the activation enthalpies of diffusion of the transition-metal elements turned out to be considerably higher than those measured for the non-transition-metal elements. The present study shows that the diffusion of Ni atoms is likely to proceed by a vacancy mechanism via Al and Pd sites.