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MM: Fachverband Metall- und Materialphysik

MM 29: Nanostructured Materials II

MM 29.1: Vortrag

Mittwoch, 24. März 2010, 12:00–12:15, H16

Diffusion-induced recrystallization in Ni/Pd bi-layers — •Michael Kasprzak, Dietmar Baither, and Guido Schmitz — Institut für Materialphysik, WWU Münster, Germany

In size-mismatched thin film interdiffusion couples Diffusion-Induced Recrystallisation (DIR) appears instead of the conventional continuous Fickian atomic transport. The new grains formed during this process reveal characteristic composition levels which are so far not understood.

We study this effect in sputter-deposited Ni/Pd films in order to derive a physical interpretation of the preferred compositions. After heat treatment, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry show that new grains are indeed formed inside the diffusion zone. Characteristic concentration levels for Ni/Pd are derived from XRD data.

A thermo-mechanic model is presented, which determines the thermo-elastic driving force to grain boundary migration. The model assumes that the gradients of Gibbs free energy of the new grain volume behind and of stressed matrix ahead of the moving grain boundary are equal in local equilibrium. This allows the determination of composition and stress in front of the boundary. Remarkably, just those grains which reveal a composition leading to the maximum possible stress in front of the moving grain boundary dominate the diffusion zone by fastest growth. According to our measurements these stresses are rather high, close to the theoretical maximum strength of the material.