Dry friction and wear properties of several hard coating combinations

According to the design requirement of friction pairs in MicroElectroMechanical Systems (MEMS), four kinds of hard coatings TiN, TiCN, AlTiN and diamond like carbon (DLC) were selected to form 16 kinds of combinations. The tribological characteristics of the 16 kinds of combinations were investigated by using ball-on-disc tester. The wear mechanisms of the coating combinations were analyzed by scanning electron microscopy (SEM), Energy-dispersive spectroscopy (EDS) and Raman spectroscopy. The results show that the combinations of AlTiN balls/different coated discs and DLC discs/different coated balls have smaller wear and friction coefficient (less than 0.2). Among them, the wear mechanism of the friction pairs composed of AlTiN balls and four kinds of coated discs is extremely slight abrasive wear. The wear mechanism of the combinations of DLC discs and the coated balls (except for the AlTiN ball) is mainly adhesive wear, accompanied by slight abrasive wear. Furthermore, in the design of the coating combination, the coating with high hardness and good wear resistance should be chosen as the fixed part, while the coating with slightly lower hardness and surface roughness is selected as the moving part. Such design principle can ensure good tribological characteristics of coating friction pairs in the MEMS.