Wear Scar Microstructure and Anti-wear Mechanism of the Magnetron Sputtered Ag Film

Silver film was prepared on copper substrate by magnetron sputtering method, and current-carrying friction experiments were carried out. The maximum contact resistance was obtaided under the load of 5 N and voltage of 1.5 V, and the microstructure of this wear scar was studied further. The laser confocal microscope (LSCM), transmission electron microscope (TEM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) analysis techniques were used for observation and analysis of the wear scar microstructure. From the SEM Morphologies, the wear scar surface was smooth and uniform, some furrows, pitting and plastic flow were visible by magnifying observation, and some accumulation and peeling were found in the edges of the wear scar. Some irregular shaped large pitting may formed by plastic deformation, and the formation was also likely to be related to the conductive grease. While, the small pittings with regular shape may formed by friction heat. It was concluded that the flow and accumulation of the Ag film surface were used by the copper ball extrusion, and the grain composition of the Ag film changed during current-carrying friction. Ag particles were found in the wear scar surface, which come in the shape of short rod and spherical ranging in the size 20~150 nm. These little particles would form different crystalline grains, and the average size of the grains was 582 nm calculated by EBSD. Most of the grains were very fine, and fine-grain strengthening of the wear scar microstructure improved the mechanical and tribological properties. By the EBSD analysis, there were (012) and (111) preferred orientations in the microstructure of the wear scar, as the family of crystal faces (111) was the most densely arranged faces of face-centered cubic metal material, such as silver, so that the (111) preferred orientation was beneficial to the tribological properties, but the (012) preferred orientation contributed little to the tribological properties. From the TEM Morphology, some twin silver structure were visible in the microstructure of the wear scar, and lots of 111 crystal plane family stacking fault structure were found between the twin boundaries. The EBSD calculation result shows that the proportion of (111) preferred orientations twin silver reached 93.5%. The high-density twin silver inclusion non-twin crystal microstructure was good to the internal slippage and the wear resistance. The existence of twin dislocation making it easy to slip between grain boundaries, which may be the fundamental reason for theanti-wear properties of Ag film. However, to confirm the proper proportion of twins and non-twin(soft grains), the nanotribological mechanism of the Ag film should be studied further.