Tribofilm surface roughness

XANES spectroscopy has been used to study the composition and mechanism of antiwear tribofilm formation. The absorption XANES spectra were recorded in total electron yield (TEY) versus fluorescence yield (FY) detection to investigate the chemical nature of P, S, Ca, O and Fe on the surface and in the bulk, respectively. The application of XANES surface TEY mode which analyzes the top 5 nm layer, and the FY technique which analyzes the 50 nm layer of the bulk, taken together, give a marvelous opportunity to study nondestructively the antiwear tribofilms. Both techniques can be used under a wide variety of conditions e.g., the formation of tribofilms at different rubbing times, load, concentrations, temperatures and surface roughness (Kasrai et al., 1993 and 1996 Koningsberger and Prins, 1988 Martin et al., 2001 Yin et al., 1997a). 

C) The effect ofphysical parameters on tribofilm chemistry. The effect of physical parameters (adsorption, rubbing, temperature, concentration, load, surface roughness, tribofilm thickness) and on the chemistry of tribofilms was studied by many investigators, see Table 4.3. 

Physical parameters By using Table 4.3. The effect of physical parameters such as adsorption, rubbing, temperature, concentration, load, surface roughness on antiwear performance of ZDDPs , which term is described by the physical parameter (a) the tribofilm accumulated on the surface becomes thicker with adsorption time (b) long-chain phosphates are formed on the topmost surface, but short-chain phosphates were present in the bulk (c) sulfur and phosphorus ratio changes with rubbing time and (d) when load increased the concentration of (S) and decreased that of (P) ... 

These presumptions are based on the results of chanical composition analyses and structural determinations by beam-based analytical methods. To verify the mechanisms involved, it is essential to clarify the frictional and mechanical properties of each layer in the multilayered structure of the tribofilm. Most importantly, with respect to the uppermost surface and the underlying area, which are thought to control the macroscale friction behavior, it is indispensable to determine differences not only in surface roughness, but also in shear strength and frictional behavior relative to depth on a nanometer scale. It is also important to make clear the distribution of the chemical composition relative to the tribofilm depth and to make this chemical distribution consistent with the nanometer-scale frictional and mechanical properties. However, estimating these properties experimentally on a nanometer scale is a difficult task, although several attempts have been made [24-28],... 

The aforementioned nanoprobe and beam-based analyses results made clear the differences in surface roughness, mechanical/frictional properties, surface nanostructure, chemical composition, and surface chemical state on a nanometer scale between the MoDTC/ZDDP and ZDDP tribofilms. These results demonstrated that the nanostructural, nanometer-scale mechanical and chemical properties acted as the controlling factors in the macroscale friction behavior of the tribofilms. From these results, a microstructure model of the tribofilms was developed to explain the mechanism of friction reduction, as shown in fig. 9.20 [3, 34]. 

Drummond et al. studied properties of transfer films formed during friction tests of IF-WS2 or 2H-WS2 dispersions in tetradecane between two mica surfaces. First, they proved that fiansfer film is formed under shear, but not under hydrostatic pressures [45]. Transfer films obtained from fullerenes are made of small and very thin islands (1.2 to 2.4 nm) distributed in a homogeneous way on surfaces. Tribofilm obtained with 2H is rough and disorganized and is composed of particles from 15 to 40 nm in height and 0.1 to 0.8 pm broad. 

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