Determination of the Mechanical Behaviour of Thin Films on Substrate Systems from Micromechanical Experiments

Micromechanical tensile experiments in a Scanning Electron Microscope (SEM) allowed us to identify and follow the activation of a variety of different deformation mechanisms, on several sorts of films on substrate systems. The investigated systems consisted of SiO2 and YF3 films deposited on copper and aluminium substrates, with or without an interlayer. The experimental results show that the mechanical response of the films differs, in particular, with respect to the interface response: the cracking activity will depend on the film adhesion. An attempt is made to relate the microstructural parameters of the assembled materials with the observed mechanisms, through models which are based on the shear lag formalism. Critical parameters of the systems under stress are determined and compared to theoretical calculations: critical stresses and strains for cracking, stress transfer lengths, interfacial fracture energies. The approach gives some insights on the mechanical response of films on substrate systems submitted to a tensile state of stress.