Nanoindentation as a tool for characterising the mechanical properties of tribological transfer films

In conventional pin-on-disk testing of the tribological characteristics of two different materials in sliding contact, the main parameters of interest are notably the friction and wear properties of the material pair. However, when two bodies consisting of hard and soft materials, respectively, are subjected to such testing, the appearance of a transfer film, or third body, which can be a composite mixture of the two, is often observed. This layer is formed through mutual transfer and/or by mechanical mixing of the two materials. Until now, the characterisation of transfer films in terms of their mechanical properties has been hampered by their non-homogeneous distribution across a tested surface, their small size, low thickness and the difficulty in accurately positioning a test probe such that the film properties can be measured independently from those of the substrate.