Determination of the inherent friction characteristic of ZnDTP-derived tribofilms formed inhomogeneously over the contact surfaces

To determine the friction characteristic of ZnDTP-derived tribofilms, we made microscopic measurements of friction across the tribofilm under dry conditions to eliminate possible hydrodynamic action of the fluid, using a laboratory-made micro-tribometer. The friction traces showed large fluctuation during the measurement across the tribofilm due to the inhomogeneous formation of the tribofilm. We assigned measuring points of the friction coefficient using a micro-tribometer across the tribofilm point-by-point to the surface images obtained with a confocal laser microscope, SEM images, and EPMA chemical images. Based on our results, we propose a data processing method to correlate the local friction to the morphology or the local chemistry of the tribofilm. The effect of the alkyl chain of ZnDTPs is also discussed.