Effect of annealing treatment on the microstructure, mechanical and tribological properties of chromium carbonitride coatings

Chromium nitrides were deposited by RF reactive magnetron sputtering from a Cr target on high carbon steel substrates XC100 (1.17 wt% carbon) in a N-2 and Ar gas mixture. In order to investigate the formation of chromium nitrides, carbide and carbonitride compounds were subjected to vacuum annealing treatment for 1 h at various temperatures ranging from 700 to 1000 degrees C. The samples were characterized by EDS, XPS, XRD, SEM, nanoindentation and tribometry. The results showed the emergence of Cr2N and CrN during the early stages of annealing and the appearance of chromium carbonitride phases only at 900 degrees C. The (111) preferred orientation of the fcc CrN phase was changed to (002) at 900 degrees C in parallel with the appearance of chromium carbides. Nanoindentation tests revealed a gradual increase of the Young's modulus from 198 to 264 GPa when increasing the annealing temperature, while the hardness showed a maximum value (H = 22.4 GPa) at 900 degrees C. The low friction coefficient of the Cr-C-N coating against a 100Cr6 ball was approximately 0.42 at 900 degrees C. The enhancement of mechanical and tribological properties was attributed to the stronger bonding Cr-C at the CrN/XC100 interfaces as confirmed by XPS results.