Tribological Properties of Phosphorus and Sulfur-Free Organotungstate Additive on Plasma Nitrided Surface of Bearing Steel

The tribological properties of phosphorus and sulfur-free organotungstate additive were studied on the substrate and plasma nitrided surfaces of bearing steel.The friction and wear test was carried out systematically on four-ball friction and wear tester.The composition and chemical states of friction reaction film were analyzed by using XPS and SEM.The results showed that the friction coefficient and worn scar diameter on the nitrided surface of bearing steel were smaller than those on the substrate surface,with the reduction of friction coefficient obvious up to 24.8% and the decrease of worn scar diameter to 7.2%.Compared with the substrate surface,the nitrided surface of bearing steel possessed a superior wear resistance owing to the WN formed in the friction reaction film and a stronger adsorption of organic carbon chain and the W element,which led to the higher contents of C and W element and the better friction-reducing properties.