Boundary lubrication of steel surfaces with borate, phosphorus, and sulfurcontaining lubricants at relatively low and elevated temperatures

Prolonging the life of engineering components through lubricant formulation to achieve better wear resistance and higher oxidation stability is of par amount importance to many mechanical systems, such as automotive gears and bearings. This can be accomplished with formulated lubricants that limit th e generation of wear debris causing severe abrasion and protect the contact ing surfaces through the formation of wear-resistant tribofilms. In this st udy, a ball-on-disk tribometer was used to characterize the friction and we ar properties of steel surfaces slid in the boundary lubrication regime. An experimental scheme was developed to allow the statistical screening of va rious lubricant formulations. Sliding experiments were performed in baths o f different lubricants at relatively low and elevated temperatures, approxi mately 32 and 100 degrees C, respectively, under conditions of constant loa d and sliding speed. Surface profilometry, optical microscopy, and scanning electron microscopy were used to characterize the dominant friction and we ar mechanisms. The tribological properties were found to strongly depend on the temperature and the additives (e.g., berate, phosphorus, and sulfur) p resent in the blended lubricants. The superior high-temperature wear perfor mance of the lubricant with the higher berate content is indicative of the formation of a durable tribofilm that reduces metal-to-metal adhesion, mate rial transfer, and surface plowing by weal debris.