Enhanced tribological performance of electroless NiP hybrid composite coatings: the role of MoS ₂ -Gr solid lubricants at room and elevated temperatures

The present study focuses on the development of electroless NiP hybrid composite coating with MoS2 and Gr solid lubricants to improve its tribological properties at room and elevated temperatures. NiP-MoS2-Gr hybrid composite coating was deposited on the AISI 1040 steel, and heat treated at 400 °C. The coating characterizations were carried out through Scanning Electron Microscopy, Energy-dispersive X-ray spectroscopy, and X-ray Diffraction techniques. The microhardness and surface roughness were evaluated on the uncoated and coated specimens, followed by the tribological evaluation at room and elevated temperatures (350 °C) against the hardened EN31 alloy Steel Pin. The test results revealed that the incorporation of solid lubricants in the NiP matrix significantly influences the physical and tribological properties of the specimen. Superior friction and wear resistance were observed in the NiP-MoS2-Gr hybrid composite coatings in both tribological testing conditions. The lowest CoF of the NiP-MoS2-Gr hybrid composite coating (0.28) at elevated temperature wear studies demonstrated the superior lubrication effect and enhanced thermal stability of the MoS2 and Graphite particles. The presence of elements such as Ni, P, Mo, S, and C on the worn surface revealed that the coating still adheres to the EN8 Medium Carbon Steel substrate, which denotes the enhanced adhesion strength of the NiP-MoS2-Gr hybrid composite coating.