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

This paper presents the results of an experimental study of Ni solute diffu sion in the single-grain icosahedral quasicrystalline compound Al70Pd21Mn9. Ni solute diffusion coefficients were measured over a temperature range fr om 699 to 1074 K. The radiotracer technique in combination with serial sect ioning of the diffusion samples was used to determine concentration depth p rofiles. No deviation from Arrhenius behaviour was detected in the temperat ure range covered by the present experiments. The results are compared with the available diffusion data on quasicrystals and on diffusion in Al and v arious diffusion mechanisms proposed for quasicrystals are discussed. The m ost striking fact is that the diffusion of Ni and the diffusion of other tr ansition-metal elements are found to be much slower than diffusion of non-t ransition-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 fo r the non-transition-metal elements. The present study shows that the diffu sion of Ni atoms is Likely to proceed by a vacancy mechanism via Al and Pd sites.