1 - Erich Schmid Institute

Aim of the Dissertation
The aim of this work is to develop a FIB-based cantilever method that allows the determination
of residual stress profiles in near-surface structures on a nanoscale. Furthermore,
special attention is paid to the effect of residual stresses and their distribution on the
fracture properties of thin films.
The determination of distributions of residual stresses in thin films is an issue of great
importance owing to their significant influence on the lifetime of coated components.
Most of the methods available measure the mean values, which can lead to a significant
over- or underestimation of the stresses when the coating exhibits a pronounced stress
gradient. Two types of techniques, based on Raman spectroscopy and X-Ray diffraction,
respectively, allow the determination of depth profiles of residual stresses, but the
materials investigated need to be either Raman active or crystalline and the complex calculation
procedures sometimes involve sophisticated simulations. The method developed
in this dissertation can be applied to a broad range of materials and allows the precise
determination of depth as well as spatial stress profiles.
Along with the residual stresses, the actual fracture properties are of great importance
for the structural integrity of coated systems. Compared with bulk materials, the determination
of strength and fracture toughness of thin films is not a straightforward task.
The main challenges are the small dimensions of thin films and the complicated stress
state in the material as a result of superimposing the residual stresses and the stresses
induced by the loading. The technique presented in this work is based on the determination
of the depth profile of residual stresses and the subsequent testing of FIB-fabricated
microcantilevers with a microindenter. The information about the stress profile as well
as the simple specimen- and loading geometry allow a precise and reproducible determination
of strength and fracture toughness.
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