Litian Hu

The Influence of Total Acid Number of Ester Oil in Tribological Behavior of DLC Contacts

The synergetic lubrication effects between diamond-like carbon (DLC) coatings and lubricating oils have draw much attention for the past decades, and promising results have been reported between DLC and biodegradable synthetic ester, which might be a potential solution in energy conservation and environmental protection. However, the challenges lie in that the synthetic ester oils exhibit lower oxidation stability than the hydrocarbon oils and are prone to produce organic acids in the aging process. Thus, investigating the tribological behavior of DLC coating in acidified ester oil is meaningful to the long-term reliability of ester-lubricated DLC contacts. In this article, the friction and wear behavior of DLC–DLC, DLC/steel, and steel–steel contacts in acidic ester oils with different total acid values (TANs) is systematically studied. It was found that acidification of ester oil showed certain beneficial tribological effects for the self-mated steel and DLC contacts but could cause severe wear loss on steel counterparts with a special polished appearance for steel–DLC hybrid contacts. By focusing on the properties of the tribofilm formed on the contact surfaces, a possible tribological mechanism was discussed. Finally, it was proposed that the steel–DLC contacts exhibited low tolerance to organic acids and thus the additives that could dissipate the produced organic acids are a critical component in lubricating oils that were tailored for the steel–DLC contacts.

The extreme pressure and lubricating behaviors of potassium borate nanoparticles as additive in PAO

ABSTRACT The potassium borate nanoparticles (nPB) as lubricant additive were prepared with an eco-friendly method. The tribological properties of nPB and ZDDP as lubricant additives in polyalphaolefin (PAO) were systematically evaluated using a four-ball tribometer and a SRV fretting friction and wear tester, which suggested that nPB exhibited excellent extreme pressure capacity, and better anti-wear and friction-reducing properties than ZDDP. Results of surface analyses show that the good lubricating properties and excellent load-carrying capacity of nPB in PAO are ascribed to the boundary protecting films, which were composed of some easy-shearing compounds: B2O3, FexBy and Fe2O3.