Nanoindentation and friction studies on Ti-based nanolaminated films

Abstract

Multilayered Ti/TiN and Ti/Cu films of 12–15 μm thickness were produced using an r.f. triode-magnetron sputtering technique. The thickness of Ti layers in both types of composites varied between 150 and 1000 nm. TiN and Cu layers were thinner, and their thicknesses varied within a narrower range of 20–120 nm. The volume fractions of the constituents in the composites were kept constant in order to study the effect of reducing Ti layer thickness (λ Ti) on the mechanical and tribological properties of the laminates. Nanoindentation tests were performed to determine hardnesses and elastic moduli of the composites and to analyze the energy expenditure during the indentation process. The elastic modulus and hardness of the Ti/TiN films were both higher when tested in a direction parallel to the plane of the layers compared to a direction normal to their planes. The strength of Ti/TiN also increased with (λ Ti) and showed a good agreement with the strength levels calculated by considering the difference in the elastic moduli of the constituents on the basis of the Koehler strengthening mechanism. Thin Cu layers in Ti/Cu were not effective as barriers to dislocation motion, and Ti/Cu interfaces were susceptible to delamination during indentation tests and sliding wear tests. A linear relationship was observed between the wear rates of Ti/TiN and (λ Ti) −0.5 which suggests that the wear resistance of the laminated composites can be improved by reducing the distance between the TiN layers.