Enhancement of heavy-duty friction and wear characteristics of cast-iron surface by electrolytic micro-textures filled with MoS2

Abstract

Cylinder liners made of cast iron are widely used in heavy-duty diesel engines. With the continuous strengthening of heavy-duty conditions of diesel engine, surface modifying technologies of piston ring and cylinder liner are gaining more attention. Two types of modified surfaces were prepared using cast-iron cylinder liner. One was a micro-texture prepared by electrolytic machining technology and the other was a MoS2-filled micro-texture prepared by cathodic reduction of thiosulfate. Modified cast-iron cylinder liners matched with chromium-based ceramic composite coated (CKS) rings were compared using the piston ring reciprocating liner test rig. Friction coefficient and wear depth of MoS2-filled microtextured liner were 8.4% and 51.5% lower than those of the microtextured liner under the simulated conditions of 50 MPa, 200 r/min and 250 °C, respectively. XPS of the MoS2-filled micro-textured surface revealed that both zinc dialkyl dithiophosphates (ZDDP) in the lubricating oil and MoS2 in the micro-textures were involved in the formation of the tribofilm with a good synergistic interaction. Typical compositions of friction-reducing and wear-resistant tribofilm on the platform area between the MoS2-filled micro dimples contained some amount of the zinc compounds ZnO, the short chain polyphospahtes FePO4, the unoxidized molybdenum compounds MoS2 and the sulfides FeS.