Effect of carbon content on structural, mechanical and tribological properties of Cr-V-C-N coatings

• Cr-V-C-N coatings were deposited using magnetron sputtering technique. • The carbide and nitride phases were detected in the Cr-V-C-N coatings. • All Cr-V-C-N coatings exhibited dense and columnar morphology. • Carbon promoted the grain refinement of the nanocrystalline Cr-V-C-N coatings. • Cr 0.22 V 0.21 C 0.28 N 0.24 coating presented the best tribo-mechanical behavior. Cr-V-C-N thin films were deposited on XC100 steel and Si(100) wafers by a radio frequency magnetron sputtering technique using chromium and vanadium targets in an Ar/N 2 /CH 4 mixture atmosphere. The microstructure, mechanical and tribological properties of coatings were investigated as a function of carbon content. It has been found that the quaternary Cr-V-C-N coatings containing a low percentage of carbon (≤ 12.4 at.%) exhibited a mixture of chromium and vanadium nitrides nano-sized crystallite phases. The coatings containing a high carbon content (> 25 at.%) were consisted of nitride and carbide phases, where the large carbon atoms inserted through CrN and VN. Mechanical properties of the Cr-V-C-N coatings were influenced by the carbon addition. The maximum hardness value of 28.3 GPa was obtained for the coating containing 28 at.% of carbon which is related to the adhesion strength enhanced by the formation of carbide and nitride mixture. Addition of carbon into the Cr-V-N coating led to significantly decrease its friction coefficient from 0.63 to 0.47. The formation of carbides through the dispersion of carbon in the grains effectively improved the density of the Cr-V-C-N coatings so that the coating deposited under a high CH 4 flow rate exhibited a better wear resistance than the other Cr-V-N and Cr-V-C coatings.