Tribological synergistic effects between plasma nitrided 52100 steel and molybdenum dithiocarbamates additive in boundary lubrication regime

•The synergistic effects between plasma nitrided steel and MoDTC were investigated.•Better friction reduction and wear resistance were exhibited on nitrided surface.•No induction phase exhibits in friction coefficient curve for nitrided steel surfaces.•More amounts of MoS2 and absorbed carbon were formed in the tribofilm of nitrided surface.•The synergistic effects were attributed to the hard nitrided layer and the tribofilm.

The interactions and synergistic tribological effects between plasma nitrided 52100 steel and molybdenum dithiocarbamates (MoDTC) additive under boundary lubrication were studied in this work. The tribological behaviors of plasma nitrided and untreated steels under lubrication with different MoDTC concentrations were examined on a four-ball friction and wear tester. The results showed an obvious synergistic effect between plasma nitrided steel and MoDTC additive. The synergistic effect indicated a lower friction coefficient without an induction phase and a higher wear resistance, which was attributed to more amount of MoS2 and absorbed carbon were formed in the tribofilm of the nitrided surface.