Tribological properties of DLC coatings with varying Cr concentration in water lubrication

Hydrogen-free amorphous carbon (a-C) coatings with five Cr contents were synthesized by unbalance magnetron sputtering aiming to evaluate the influence of Cr contents on microstructure, mechanical and water-lubricated tribological properties sliding against ceramic balls, and subsequently located the range of optimum deposition parameters and determined material of counterparts. The Cr atomic percentage exhibited upward tendency from 3at.% to 14.09at.% as the Cr target current increased from 0.5A to 2A. The incorporation of Cr enhanced the hydrophobicity, but decreased the hardness of a-C coatings. The Cr content of 4.9at.% was a critical value which determined the microstructure and tribological properties of Cr/a-C coatings. Below this value, the Cr/a-C coatings exhibited similar microstructure and friction behavior with pure a-C coatings. However, above this value, the Cr/a-C coatings exhibited obvious Cr-C bonds and confronted higher friction coefficient (0.675 for Al2O3, 0.868 for Si3N4) and specific wear rate(~10-5mm3/Nm). The SiC as counter-balls displayed lower friction coefficient and specific wear rate compared to other material balls