Regensburg 2002 – scientific programme
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SYME: Mechanical Properties of Thin Films
SYME 3: Mechanical Stresses and Plasticity
SYME 3.2: Talk
Tuesday, March 12, 2002, 11:45–12:00, H 4
Study of the yielding and strain hardening behavior of thin metal films using discrete dislocation simulations — •Burghard von Blanckenhagen1, Peter Gumbsch2,3, and Eduard Arzt1 — 1Max–Planck–Institut für Metallforschung, Stuttgart — 2Universität Karlsruhe, Institut für Zuverlässigkeit von Bauteilen und Systemen — 3Fraunhofer Institut für Werkstoffmechanik, Freiburg und Halle
The flow stresses of polycrystalline thin metal films are much higher than the flow stresses for the corresponding bulk material and scale approximately with the inverse film thickness. Discrete dislocation simulations, are well suited to investigate dislocation glide in a thin film because configurations can be treated which are not tractable analytically and the number of dislocations is still relatively small due to the confined geometry.
It was found that models based on moving dislocations which extend over the whole film thickness either can not explain the high flow stresses measured experimentally or give a wrong scaling with the film thickness, even when the interaction with other interface–dislocations is taken into account.
As a consequence, the operation of dislocation sources in small grains was simulated. A new model is proposed, which is based on the assumption that the number of dislocation sources per grain is small and therefore requires multiple activation of a source. This model predicts flow stresses in good agreement with experimental data and explains the observed scaling behavior of the flow stress with the film thickness.