An Experimental and Theoretical Study on the Effect of Nitriding on the Running-In Behavior of Lubricated Sliding Contacts

Enhancing the wear-resistance of mechanical elements is always of much interest for the end users as well as the manufacturers. One common method for surface treatment is nitriding. In this research, friction and wear of nitrided and unnitrided disks are experimentally and numerically studied. The experiments are conducted using pin-on-disk test rig on samples made from 4140 steel. A numerical model based on the load-sharing concept has been developed to predict the friction coefficient, surface's temperature, film thickness, and wear rate. The lubricant temperature along with the friction coefficient is used to predict the wear volume using the fractional film defect theory. The results for un-nitrided disks indicate that increasing the speed results in a higher lubricant film thickness and thus the wear volume decreases. Increasing the applied load, on the other hand, results in a decrease in the film thickness and as a result the wear volume increases. In the nitrided case, the wear volume is a function of load only and does not depend on the speed. The diagrams of wear volume versus sliding distance shows a running-in period approximately before 1500 m after which the wear rate stabilizes. Friction coefficient and wear volume results are shown to be in an acceptable agreement with the simulation results.