In this paper amplitude attenuation theory is used to predict film thickness variations caused by shallow indentation inside a rolling-sliding elastohydrodynamic (EHL) contact. The model providing a complete analytical description of roughness passage through the contact is considered. The estimation model is compared with film thickness measurement obtained by optical interferometry. The in-contact effects for several shapes of indentation were simulated. It is clearly shown that optimal indentation profile should have smooth shape with large diameter and small depth. The results were generally explained on theoretical curves which bring a clear insight into the transient phenomenon and can be used as a rapid engineering tool.
The wear mechanism of diamond-like carbon (DLC) in hot, pressurized water has been studied by the oxygen depth profile of DLC films pre and post a sliding test. The sliding test between DLC films coated on chromium molybdenum steel (JIS SCM420) pins and austenitic stainless steel (JIS SUS316) plates was conducted in a water environment by using high temperatures of 100, 200, 250 and 300°C and a high-pressured (10 MPa) autoclave friction tester. The dissolved oxygen concentration (DO) was 0.52 mg/L for oxygen-poor water and 40 mg/L for oxygen-rich water. The experimental results showed that the specific wear rate of DLC was strongly related to the water temperature and the DO concentration. The specific wear rate in both cases of oxygen-poor and oxygen-rich water showed a temperature dependency. When the temperature was below 200°C, the specific wear rate of DLC did not depend on the DO concentration. On the other hand, when the water temperature was more than 200°C, the specific wear rate drastically increased with the DO concentration. In order to prove the effect of oxidation on the wear rate of DLC, the depth profile of the oxygen concentration was compared to that of the carbon concentration on the inside and outside of the wear scar of DLC after sliding tests in hot, pressurized water. When the concentration of DO in the water was low at 0.52 mg/L, the O/C ratio was not affected by the water temperature. On the other hand, when the concentration of DO in water was high at 40 mg/L, the O/C ratio of the top surface increased from 0.05 to 0.18 with an increase in the water temperature on the inside of the wear scar of DLC, where the O/C ratio on the inside of the wear scar was higher than that on the outside of the scar. On the basis of the estimated rate of reaction between DLC and oxygen, determined from a linear relationship between ln (Oxidation wear volume) and the inverse temperature, it was concluded that the oxidation of DLC governed the wear of DLC in hot, pressurized water. Friction was found to enhance the oxidation wear of DLC from the estimated activation energy.