Effect of the Cr content on the mechanical properties of nanostructured TiN/CrN coatings

This article reports on the mechanical properties enhanced by the variety of Cr content in the nanostructured TiN/CrN coating system. The coatings were synthesized using a closed field unbalanced magnetron sputtering method with separate Ti and Cr targets and characterized in terms of chemical composition, crystal orientation, layer structure and mechanical properties. The nanostructured TiN/CrN coatings synthesized in this work have a range of atomic concentration ratio of X=Cr/(Ti+Cr) from 0.15 to 0.59. The results from high-angle and low-angle XRD analysis show that the coating with X=0.15 is not a multi-layered film but a composite film of a mixed TiN and CrN with a grain size of approximately 16 nm. The hardness (H) of coatings was strongly dependent on the value of X and the maximum hardness and plastic deformation resistance (H3/E2) of approximately 41 and 0.36 GPa, respectively, were measured for the coating with X=0.15. These values are 1.6 and 3 times higher than those of the single TiN coating (27 and 0.12 GPa), respectively. Also, the wear resistance was largely increased than that of the single TiN coating. These enhancement of mechanical properties in the coating with X=0.15 could be attributed to the CrN doping effect, which has reduced the TiN grain size.