Paper AS-ThP2
XPS and AES Characterization of Tribofilm Formation on Non-Metallic Coatings Using ZDDP and Ionic Liquid Lubricant Additives

Thursday, October 22, 2015, 6:00 pm, Room Hall 3

Interactions between oil additives and non-metallic surfaces are less well understood than tribofilm formation on metallic surfaces. The most common anti-wear additive for metallic surfaces is zinc dialkyldithiophosphate (ZDDP). In this study, ZDDP and a phosphonium–organophosphate ionic liquid (IL) are used with three hard coatings (AlMgB14– TiB2, TiB2, and diamond like carbon), to determine what, if any, tribofilms are formed when sliding against a steel ball. Systematic characterization was conducted on the coating wear scars including top surface morphology imaging and elemental mapping, layer-by-layer chemical analysis, and cross section nanostructural examination. For boride coatings, tribofilms formed by ZDDP+IL are up to 50-70 nm thick with 75-80% surface coverage. On the other hand, tribofilms on DLC were <25 nm thick and only covered 20-30% of the contact area. The presence of iron compounds in the tribofilms suggests a critical role for wear debris in tribofilm formation. In addition, oxidation products of TiB₂ were detected in the tribofilms. No involvement of the DLC surface in tribofilm formation was observed. Results suggest that wear debris digestion and contact surface reaction both are critical in tribofilm formation: the former process is responsible in forming the bulk of the tribofilm and the latter provides strong bonding of the tribofilm to the contact surface. In this poster, the emphasis will be how scanning Auger microanalysis and x-ray photoelectron spectroscopy were used for characterizing the ZDDP+IL-derived tribofilms.