Influence of CrB₂ target current on the microstructure, mechanical and tribological properties of Cr-B-C-N coatings in water

Cr-B-C-N coatings with different boron contents (24.6-27.2 at%) were deposited on Si(100) wafers and 316L stainless steels by using closed-field unbalanced magnetron sputtering via adjusting the CrB₂ target current. The microstructures, mechanical and tribological properties of Cr-B-C-N coatings in water were characterized by using XRD, XPS, SEM, nano-indentation and ball-on-disk tribometers. The results showed that the soft amorphous BN phases were formed when boron elements were introduced into CrCN coatings. With an increase in the CrB₂ target current, the B content increased from 24.9 to 27.2 at%, which caused the a-BN content in CrBCN coatings to increase gradually, and then the hardness of CrBCN coatings decreased from 18.6 ± 0.86 GPa to 16.3 ± 0.28 GPa. Due to the formation of H₃BO₃, the friction coefficient and wear rates of CrBCN/SiC tribopairs were lower than those of CrCN/SiC tribopairs. When the CrBCN coatings (25.1 at% B) were deposited at the CrB₂ target current of 3 A, the lowest values of friction coefficient (0.16) and wear rate (2.1 × 10^-7 mm³ N^-1 m^-1) were obtained simultaneously.