Microstructural optimization and anti-wear performance of supersonic atmospheric plasma sprayed nickel based self-lubricating coatings under heavy load

Abstract The aim of this work is to explore high-property nickel based self-lubricating coatings to meet the challenge of the increasing demand of heavy load wear condition. Thus, a series of Ni-MoS2/graphite coatings were designed and prepared by supersonic atmospheric plasma spraying. The microstructural evolution of lubricating phases was systematically studied by plasma focused ion beam (FIB) and field-emission transmission electron microscopy (FE-TEM). The results suggested that the lubricating phases, such as graphite and MoS2, can transform into some independent lamellar structures due to their low binding energy. MoS2 phase was easy to decompose into nanoscale Mo with preferred (110) crystal plane at high temperatures, leading to the decrease of self-lubrication property of coatings. Due to the rapid formation of the graphite-dominated debris transfer layer, the coating with approximately 19 vol% graphite showed the longest friction time and the lowest wear rate. The graphite with a large size range (1–60 μm) not only effectively compensated the loss of MoS2 caused by the thermal decomposition, but also improved the density and fracture toughness of coatings. In addition, the content of monoclinic β-MoO3 was significantly decreased with the addition of graphite, which further improved the tribological properties of the coatings. This work provided an in-depth understanding for the development of composite coatings with high anti-wear performance under heavy load.