Formation of the third bodies of steel sliding against brass under lubricated conditions

This work investigates the formation mechanism of the third bodies for brass under lubricated conditions. A tribometer based on on-line and radio-nuclide technique (RNT) techniques is used to perform the sliding experiment of brass versus steel. The microstructure, micro-hardness and chemical composition of the third bodies are analyzed by mean of the scanning electron microscope (SEM), focused ion beam microscope (FIB), transmission electron microscope (TEM), hardness testers and X-ray photoelectron spectroscopy (XPS). The results indicate that the contact pairs show good tribological behaviors and the layered third bodies (mechanically mixed layer (MML), grain refinement zone (GRZ) and plastic deformation zone (PDZ)) are formed on the brass surface during sliding. The formation mechanism of the third bodies is explored. The MML gradually forms on the worn surface in the later stage of the test by proceeding of oxidation reactions. Due to the severe plastic deformation caused by sliding, the interactional dislocation movements and dynamic recrystallization (DRX) lead to the formation of GRZ with nano-scale grains. The PDZ grains lead to the shear deformation by means of friction stress. Moreover, the generation and accumulation of dislocations result in voids in the PDZ.