Adhesion of thin films on steel and separation of the energy contributions

Surfaces are more and more used to add specific properties to materials towards multifunctional systems. These properties are introduced using thin coatings deposited on the bulk material. Reliability is of prime importance for these systems and adhesion is one of the most important parameter to control and optimize. Understanding the influence of the deposition parameters on the adhesion is a very challenging issue. Methods to properly measure the adhesion are not widely used in the industry due to experimental and conceptual difficulties. Fracture approaches to measuring, describing or predicting thin film adhesion essentially remain an academic field of research. The objective of this thesis has been to conciliate these two different viewpoints. A simple and versatile adhesion testing method, the wedge opening test, has been developed with a robust data reduction scheme. A plate identical to the substrate is bonded on top of the film to allow the insertion of the wedge. The adhesion is determined using geometrical parameters only without the need to a force measurement. The most difficult parameter to measure, in the case of non transparent substrate, is the crack length. An original method based of the out-of-plane displacement field of the specimen has been validated and used during this thesis. A steady-state finite element code is used to simulate the test and to study the contribution of each layer to the total fracture energy. The simulation code allows the determination of the contribution of each layer to the total fracture energy. Specific attention is paid to the contribution of the adhesive layer which is extrinsic to the system. The dissipation in the adhesive layer can be as high as 2/3 of the total energy dissipated in the specimen during crack propagation, in the case of film thicknesses lower than one micron.(FSA 3) -- UCL, 201