Elastic Properties of Textured Nanocrystalline Thin Films

Polycrystalline thin films and coatings often show preferred orientation of grains and crystalline domains, and develop a residual stress state as an effect of the growth mechanisms. These features can be conveniently measured by means of non-contact and non-destructive X-ray diffraction. As the technique only measures a map of strains along selected directions, stress evaluation requires a suitable constitutive equation, where the expression of moduli can be far from trivial if texture effects are to be taken into account; additionally, a grain interaction model needs to be enforced to describe strain and stress distribution among grains in the aggregate, based on background assumptions. Several grain interaction models are available from literature: usually, a model or a combination of them provides a good fit of experimental data; often however underlying hypotheses are too restrictive or require unavailable information on certain microstructural parameters, leading this approach to fail. For this reason an experimental method was developed, for the characterisation of elastic properties and residual stress in thin film components by means of X-ray diffraction during in-situ mechanical testing. This thesis presents a review of major literature works describing grain interaction modelling in textured components, and their implementation in X-ray diffraction stress analysis procedures. Following, the method for experimental characterisation of thin film elastic properties is described in detail. Applications are presented in the final chapter, that illustrates selected case studies on electrodeposited coatings.