A multi-technique approach of tribofilm characterisation

The characterization of tribofilms has already been studied by various surface analysis tools for many years. The analytical techniques usually performed on this kind of samples are X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and X-ray absorption near-edge structure (XANES). XPS is interesting for chemical environment information. AES has a good spatial resolution (approx. 0.5 mum) permitting AES mapping or making AES linescans. With XANES, the polyphosphate chain length can be characterized in case of ZDDP tribofilm. AES and XPS depth profiles can also be performed in order to follow the composition of the tribofilm with depth. Therefore, coupling XPS, AES and XANES is interesting to clarify the different layer composition of the tribofilm. In this work, AES, XPS, secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) are carried out on tribofilm. made by ZDDP additives. By a SIMS analysis, information on the elemental distribution in the surface near layers can be obtained with high lateral and high depth resolution. The use of a time-of-flight (ToF) analyser allows to obtain information on all elements quasi-simultaneously resulting in a very high sensitivity. Our aim is to investigate the tribofilm in its depth and the interface tribofilm/substrate by using a multi-technique approach on the same ZDDP tribofilm. First, depth profiles (by AES XPS and SIMS) were carried out. Secondly, a transverse section made by focused ion beam (FIB) was evaluated by TEM. All results are discussed in order to give a better understanding of the tribofilm composition. (C) 2003 Elsevier B.V. All rights reserved.