High resolution characterisation of tribochemical films on alumina

This paper presents the results of the characterisation of tribochemical films produced by the sliding wear of alumina in a humid environment. The techniques that were used were field emission scanning electron microscopy (FESEM) mechanical properties microprobe or nanoindentor (MPM), atomic force microscopy (AFM), frictional force microscopy (FFM) and non-contact optical profilometry. It was found that the tribochemical films were softer than the remnant alumina on the worn surfaces, and were liable to fracture and cracking under the indenter. The FESEM showed similar features to the AFM, but because of its direct height imaging, the AFM was better at resolving and imaging small MPM indentations. The AFM also showed that the tribochemical films were composed of small rounded particles which were pressed together to form the films. Some FFM contrast is attributed to steep gradients or edges, and some to variations in surface roughness. There is, however, some contrast which cannot easily be explained by simple geometric interactions and appears to be associated with variations in surface chemistry and structure.