Sliding Wear Behavior of Cast Iron: Influence of MoS2 and Graphite Addition to the Oil Lubricant

The present study discusses sliding wear characteristics of a gray cast iron over a range of applied loads in oil lubricated condition. Effects of MoS2 and graphite addition to the oil lubricant in governing the wear behavior have also been studied. The wear rate increased with load in general with a few exceptions in the case of oil plus 5% MoS2 wherein it had a tendency to show a reverse trend in the intermediate load range. Addition of 5% graphite to the oil brought about a decrease in the wear rate without affecting seizure resistance. Increasing quantity of graphite in the oil from 5 to 10% practically did not affect the wear rate at lower loads. However, it led to significantly lower wear rates at higher loads and also offered higher seizure resistance. In the case of oil plus 5% MoS2 lubricant mixture, the wear rate of the samples was higher than that of the lubricant with 5% graphite when tests were conducted at lower loads while identical response was observed at higher loads in both cases. Seizure resistance of the samples was not affected by the addition of 5% graphite and MoS2 to the oil. The frictional heating also increased with load in general, except in the case of oil containing 5% MoS2 and 10% graphite wherein it remained practically unaffected in the intermediate load range. The presence of 5% graphite and MoS2 in the oil lubricant brought about reduced frictional heating, except in the case of oil plus 5% graphite mixture wherein the trend reversed, and oil plus 5% MoS2 leading to comparable frictional heating during specimen seizure. Increasing test duration caused higher frictional heating. Adhesion was observed to be the principal wear mechanism while microcracking assisted delamination and abrasion also contributed to material loss.