AbstractThis work investigated the effect of nanodiamond (ND) additives on the tribological properties of CrN-coated piston ring mating with the chromium-plated and BP alloy iron cylinder liners, which is one of the key friction pairs in the internal combustion engines. To enhance the dispersion of the NDs in the base oil, the surface of ND particles was modified with polyaniline via in situ polymerization. The friction and wear as well as the scuffing characteristics of the friction pair lubricated with different contents of ND composite-added base oil were evaluated by using the reciprocating tribotests, which are close to the actual conditions. The wear surface morphologies and elements distribution were analyzed to explore the wear behaviors and the associated mechanisms of friction pairs under the lubrication incorporated with the ND composites. The results show that the ND additive is beneficial for the pair of Cr liner and CrN-coated piston ring in the friction and wear as well as scuffing properties, and the best concentration of ND additive is expected to be around 1 wt%. But for the BP liner, the developed nanocomposite has a negative impact. The friction force and the wear loss of the pair lubricated by the ND composite-added oil are even worse than that tested with the base lubricating oil.
The friction and wear properties, as well as the scuffing resistance, of different piston-ring coatings mating with a chrome-plated cylinder liner were investigated. Interrupted wear tests under the lubricant starvation condition were conducted to examine the wear behavior of Cr-diamond coating (GDC) and diamond-like coating (DLC). The results indicated that the DLC coating had outstanding tribological properties (small coefficient of friction and wear loss) at 150 °C, while the GDC coating exhibited better performance at an elevated temperature (240 °C). The DLC coating had a better scuffing resistance; no material adhesion occurred for 70 min under the unlubricated condition. The interrupted wear behaviors revealed that the scuffing process of the GDC coating involved the consumption of lubricant oil with relatively stable wear, a reduction in the friction force, and the occurrence of scuffing, in sequence. In contrast, although the friction force also increased after a short period of weak friction, no scuffing was observed. This is attributed to the formation of a mixed oxide and graphitic C tribolayer.
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