Mechanical properties and failure modes of TiAl(Si)N single and multilayer thin films

Mechanical properties and failure modes of TiAlN and TiAlSiN single layer and multilayer thin films were investigated by nanoindentation measurements. It was found that alloying of silicon into TiAlN single layer led to a significant increase of hardness attributed to the reduction of grain size described by the Hall Petch effect. The mechanical properties of TiAlN/TiAlSiN multilayers were found to be very close to the average of the two constituent materials. This allows to suggest a negligible role of the interface affecting the hardness and modulus of TiAlSiN thin films. In contrast, the formation of cracks is significantly delayed and fracture resistance improved in multilayers as compared to the single layer films. The critical load for crack propagation was found to be higher in multilayer films due to a more efficient sharing of the work of indentation between the two layers with different elastic modulus. The morphology of cracks observed using atomic force microscope mainly consists of lateral microcracks parallel to the contact edge for shallow indentations. The radial corner cracks occur only for deeper indentation when the indenter reaches to the interface between the film and the substrate.