Application of phase contrast imaging atomic force microscopy to tribofilms on DLC coatings

Tribofilms formed in the rubbing surfaces are closely related to wear mechanisms and steady-state friction in sliding contacts. However, their small thickness, inhomogeneity and discontinuity are the factors that hinder the evaluation of their micromechanical properties. The phase contrast images in tapping mode atomic force microscopy allow an estimation of inhomogeneity in micromechanical properties of the sample surfaces. The purpose of this investigation is to examine how the phase contrast images contribute to the characterization of thin tribofilms. Surfaces of diamond-like-carbon (DLC) coatings before and after friction contact against a steel ball slider were investigated in this study. The chemical characteristics of the worn surfaces were studied by micro-Raman spectroscopy, Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) and these results were discussed in association with the phase contrast images. A three-dimensional simulation of the real contact area was also conducted and the pressure distribution obtained by this simulation was compared with the phase contrast image obtained at the same area.