Study of self-repair property and mechanism of nano Cu as lubricating oil additives under oscillating friction and wear

Oil-soluble nano-Cu additives were synthesized in laboratory. 1% nano-Cu particle was dispersed in SJ 15W/40 gasoline engine oil (NC) and SJ 15W/40 gasoline engine oil (SJ) was used for comparing. Its self-repair properties as lubricating oil additives were investigated by SRV oscillating friction and wear tester. Test conditions are room temperature, frequency 25 Hz, stroke 1 mm. Self-repair properties of nano-Cu additives in connection with distance and load were, investigated in terms of variation in friction coefficient arid wear volume loss with time and load. Regardless of time and load, friction coefficient and wear volume lubricated by NC are all lower relative to SJ 15W/40 oil. When load was 400 N, experiment time was as longer as 1.5 h instead of 0.5 h, also when load more than 500 N wear volume will minish than foregoing. These phenomena represent wear self-repair effect evidently. Analytical tools such as profilometer, micro-sclerometer, scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyse worn surface of steel discs. Profilometer and micro-sclerometer analysis results show that 1% nano-Cu additives contained in SJ 15W/40 lubricating oil have very good self-repair performance to steel-steel rubbing relative to SJ 15W/40 lubricating oil, it can level off and mend the worn surface. Analyses of scanning electron microscopy, X-ray photoelectron spectroscopy indicate that nano-Cu additive take place in situ tribochemistry reaction and built a self-repair deposit soft film composed of copper on the steel discs surface. The film has lower shear intensity and significant reduced friction coefficient, at the same time it can compensate wear loss of rubbing.