We have investigated the reactivity of metal-doped (Ti, WC) DLC coatings with the extreme-pressure (EP) dialkyl dithiophosphate additive. The results confirmed the chemical reactions between the EP additive and all the DLC coatings, as well as their oxidation during the tribological contacts. We measured an about 10-times higher chemical activity for the Ti-doped DLC compared to the WC-doped or non-doped DLC. The data also clearly show that even though small, some direct chemical activity between the W-DLC and dialkyl dithiophosphate is also possible without any iron catalytic effect.
COBISS.SI-ID: 11384347
We have calculated the contact temperatures for contact of diamond-like-carbon (DLC) coatings using two well-known models and compare them with results of tribological experiments and some state-of-the-art analyses of worn surfaces. The results showed that the actual surface temperatures are 100-130 °C higher than the test temperatures. A contact temperature of about 250-260 °C was found to be the required key activation criterion for chemical reactions between the dialkyl dithiophosphate extreme-pressure (EP) additive and the DLC coating.
COBISS.SI-ID: 11274267
Contact conditions are the most important factor, determining the frictional properties of textured surfaces. The effect of texturing increases with the contact size, where sufficient number of dimples need to enter into the contact. The beneficial effect of micro-dimples becomes more evident with an increase in dimple depth as well as for higher sliding speeds. However, dimple density needs to be precisely selected depending on the lubrication mode not to end up with higher friction.
COBISS.SI-ID: 1151593
Deep-cryogenic treatment improves microstructure of P/M high-speed steel by producing finer needle-like martensitic structure. Finer microstructure results in higher surface hardness and better tribological properties, especially in terms of friction and galling resistance against stainless steel. Longer cryogenic treatment times will result in finer microstructure and higher surface hardness, which has no effect on abrasive wear resistance but it considerably improves galling properties. However, when combined with plasma nitriding beneficial effects of both treatments are lost.
COBISS.SI-ID: 11451675
For un-doped DLC coatings oil additives have very minor effect on their frictional behaviour. Low additive concentrations lead to similar friction values as observed for pure oil and high ones to conditions typical for uncoated steel surfaces. Lubrication of steel/W-DLC contacts with oils containing S-based additives, on the other hand, result in improved tribological performance caused by WS2 tribofilm formation. However, the level of improvement greatly depend on additive concentration, which needs to be properly selected depending on the contact conditions.
COBISS.SI-ID: 11678491