Tribofilm thickness

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. 

Tribofilm thickness. Depth profiling results show that the 12 hour test tribofilm is much thicker than the 0.5 hour test film. The tribofilm thickness results from the balance of the rate of tribofilm growth, and the rate of removal by wear, and is not correlated to the wear scar width to any great extent (Bell, 1995 Fuller et al., 1998 and 2000 Georges et al., 1998 Jahanmir, 1987 Lindsay et al., 1993 Palacios, 1987 Yin et al., 1997a Tonck et al., 1999). ... 

From the AES depth profiles of Figure 2, it is possible to estimate the tribofilm thickness. Assuming that the etching speed in the iron oxide is the same as in the phosphate, and given that the oxide thickness is estimated at 4 nm by X-ray Photoelectron Spectroscopy XPS (ratio of iron oxide over iron metal peaks), the tribofilm thickness is estimated at about 14 nm. It is noted that AES depth profiling does not give any quantitative information. 

This paper shows the feasibility of a novel experimental analysis of the rheology of a ZDDP tribofilm. The tribofilm thickness is evaluated at about 14 nm. The test consists in partially removing the tribofilm on a steel surface and to run a friction test on the modified surface. Using triboscopic analysis of both friction and ECR measru ements, information on the tribofilm durability are visualized mder different lubrication conditions. Unlubricated contact conditions are quite severe, and the use of dodeccme lowers this severity. The use of PAO resulted in a particular case where all additives of the lubricant have been depleted. Both mechanical and chemical removal mechanisms seem to be involved. 

Adsorption. Sulfur and phosphorus ratios change with rubbing time. Tribofilms accumulated on the surface become thicker with time. All co-additives cause reduction in ZDDP surface coverage under all conditions studied. A surface force apparatus (SFA), and atomic force microscopy were used to determine tribofilm thiclaiess, molecular structure and mechanical properties. For the neutral ZDDP, monomolecular layer thickness is 1 nm and for basic ZDDP it is 1.6 nm (Sutherland et al., 1993 Bames et al., 2001 Bee et al., 1999 Dacre and Bovington, 1983 Georges et al., 1998 Paddy et al., 1990 Wu and Dacre, 1997). 

The chain lengths in FY spectra are estimated at 12, 7 and 1 in for 0.5 wt%, 1 wt.% and 2 wt% calcium phenate, respectively. Thus the topmost surface measured by TEY contains relatively long chain polyphosphates, and the bulk chemistry of the film measured by FY contains mostly shorter chain polyphosphates. The bulk FY signal is relatively strong, indicating that the films formed with calcium phenate are relatively thick (several hundred angstroms). Summary of the tribofilm compositions is displayed in Table 4.4. The (S) L-edge... 

At 150 °C, tribofilms of 6 nm or thicker were formed on the disc. When the layers had a thickness higher than 6 nm no signal from the iron oxide layer was detected and the reaction layer has to be assumed to be semi-infinite and the... 

In this work, we have evidenced the formation of a lamellar solid from the tribochemical reaction of a borated additive and a succinimide additive. The result is the formation of h-BN in the tribofilm. The tribofilm is mainly composed of an amorphous borate matrix containing highly-dispersed h-BN nanoparticles in the form of sheets less than 10 nm wide and 5 nm thick. The originality of this h-BN tribochemical reaction lies in the nature of the intermolecular reaction between the two additives. At the opposite, M0S2 formation fiom MoDTC is the result of intramolecular chemical reaction. 

The tribofilm is mainly composed of an amorphous borate matrix containing highly-dispersed h-BN nanoparticles in the form of sheets less than 10 nm wide and 5 nm thick. 

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