Influence of Si contents on the microstructure, mechanical and tribological properties of Cr-Si-N coatings

Cr-Si-N coatings with different Si contents were deposited by a hybrid coating system, where the Cr target was used for the arc ion plating (AIP) and the Si target for the middle frequency (MF) magnetron sputtering. The XRD, cross-sectional SEM and XPS results indicated that the Cr-Si-N coating exhibited a nanocomposite structure containing CrN nanocrystallines and amorphous Si3N4 phase. Furthermore, the TEM results showed that all the CrN nano-crystals were embedded in an amorphous matrix of a-Si3N4. The thickness of the Cr-Si-N coatings was in the range of 2.1-2.4 μm while the Si content was in the range of 2.2-11.1 at%. The hardness of Cr-Si-N coatings first increased and then decreased with the increase of Si content and the highest value was approximately 2490 Hv at 6.94 at% Si content. For coatings with different Si content, the average friction coefficient was maintained around 0.35-0.45. The highest hardness of Cr-Si-N coatings with Si content of 6.94 at% can be attributed to limited dislocation activity in nano-crystals and suppression of grain boundary sliding.