The application of laser scanning confocal microscopy to tribological research

Since the introduction of the first commercial systems in the early 1980s laser scanning confocal microscopy (LSCM) has become an established technique in biological and medical fields of research. To date the application of LSCM to metallurgical and tribological fields of research has been extremely limited. However, largely as a result of recent rapid advances in computer processing power, the modern LSCM system has become a flexible research tool with a broad range of capabilities, which are well suited to metallurgical research. In this article, the application of LSCM to the study of worn surfaces is discussed. Illustrations are presented which show how post-processing of confocal image stacks can be used to achieve a greatly extended depth of field thus enabling clear images of rough tribological surfaces to be constructed. Furthermore, illustrations of the use of LSCM for the quantification of surface topography are also presented which demonstrate that surface height profiles which faithfully reproduce the geometry of the real surface can be measured with a high degree of accuracy. The accuracy of profile surface roughness measurements via the LSCM has also been systematically investigated and compared with the results obtained from profiles measured using contact mode atomic force microscopy (AFM). The results presented show that, after suitable data post-processing to correct for tilt and extraneous signal noise, the results obtained using both techniques are in good agreement. Finally, the results of a study of rolling sliding contact wear surfaces of two high chromium content white cast irons are presented. The combination of extended focal depth imaging and topographical quantification afforded by the LSCM has proven capable of firmly establishing the wear mechanisms operating in these materials.