Fachbereich 11 - Physik
Institut für Materialphysik
Diffusion and Segregation in Grain and Interphase Boundaries

Diffusion and segregation in nanocrystalline Fe-Ni alloys

Nanocrystalline Fe-Ni alloys are of a great physical and technological interest due to their advanced magnetic properties. Such alloys are designed as functional engineering materials for applications, e. g. in transformer cores and recording heads. We have measured Fe and Ni radiotracer diffusion in Fe60Ni40 alloy samples which were prepared by compacting nanocrystalline alloy powder followed by a suitable heat treatment, which resulted in a thermally stabilized bimodal microstructure: nono-sized grains formed micrometer-sized agglomerates, revealing nanocrystalline grain boundaries and inter-agglomerate interfaces. The mathematical treatment was developed for evaluating interface diffusion in this bimodal microstructure. As a result diffusion in the A, B and C-type kinetic regimes was quantitatively determined. It was found that the atomic mobility in the interagglomerate interfaces is by 2 to 3 orders of magnitude faster than in the nano-grain boundaries. For silver solutes this nano-sized material was suitable to determine Ag segregation coefficients in nano-grain boundaries and to evaluate directly the Ag grain boundary diffusion coefficient.

Drittmittelgeber:

Alexander von Humboldt-Stiftung, Korean Ministry of Science and Technology

Beteiligte Wissenschaftler:

Dr. S. V. Divinski, Prof. Dr. Chr. Herzig (Leiter), Dr. F. Hisker, Dipl.-Phys. Y.-S. Kang (Hanyang University, Ansan/Korea), Prof. Dr. J.-S. Lee (Hanyang University, Ansan/Korea)

Veröffentlichungen:

Divinski, S. V., F. Hisker, Y.-S. Kang, J.-S. Lee, Chr. Herzig: 59Fe grain boundary Diffusion in nanostructured g-Fe-Ni Part I: Radiotracer experiments and Monte Carlo Simulation in type A and B kinetic regimes Z. Metallkunde, 93, 256 (2002) Part II: Effect of bimodal microstructure on diffusion behaviour in type-C kinetic regimes Z. Metallkunde, 93, 265 (2002)

Divinski, S. V., Y.-S. Kang, J.-S. Lee, F. Hisker, Chr. Herzig Tracer diffusion of 63_Ni in nano g-FeNi produced by powder metallurgical method: systematic investigations in type C, B, and A kinetic diffusion regimes Interface Science, 11, 67 (2003)