Wear prevention behaviour of nanoparticle suspension under extreme pressure conditions

This work presents and discusses the extreme-pressure behaviour of nanoparticle suspensions in a polyalphaolefin (PAO 6). CuO, ZnO and ZrO2 nanoparticles were dispersed at 0.5, 1.0 and 2.0 wt.% in PAO 6 using an ultrasonic probe during 2 min and EP properties were obtained using a Stanhope Seta Shell Four-Ball EP Lubricant Tester according to ASTM D2783. The ball test material was AISI 52100 steel of 12.7 mm diameter, with a hardness of about 65 HRC. The wear scar diameter (WSD) was measured with an optical microscope and scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analysis of the worn surface highlighted a number of conclusions: all concentrations of nanoparticles improved the EP properties of PAO 6; CuO nanoparticles exhibited the best EP behaviour and ZrO2 the worst; CuO and ZnO suspensions showed better results at 0.5% and 2.0 wt.% of nanoparticles, respectively, while ZrO2 behaved identically regardless of nanoparticle concentration; all results were analysed according to the nanoparticles' size and hardness, and their deposition on wear scar surface.