Microstructure, Mechanical and Corrosion Properties of Column-Free CrN[sub.x] Coatings Deposited by Closed Field Unbalanced Magnetron Sputtering

CrN[sub.x] coatings with a low nitrogen content below 31.7 at.% were deposited using closed field unbalanced magnetron sputtering by varying the N[sub.2]:Ar flow ratio. A dense and column-free CrN[sub.x] coating was obtained at a nitrogen content of 14.8 at.%, whereas the other CrN[sub.x] coating were all columnar structured. The column-free CrN[sub.x] coating was composed of two types of structures: an N-incorporated Cr(N) solid solution matrix with a high number of point defects and a Cr(N) matrix with dispersed Cr[sub.2]N nanocrystallines. The pinning effect of Cr[sub.2]N nanocrystallines and point defects in Cr(N) grains are responsible for the formation of a column-free CrN[sub.x] coating. The columnar-free CrN[sub.x] coating exhibits a high hardness of 33.7 GPa, which is comparable to the hardness of Cr[sub.2]N coating but 2.6 times larger than that of the Cr coating. It also has significantly better corrosion resistance than both Cr and Cr[sub.2]N coating, with a corrosion current density of 4.1 × 1.0[sup.−9] A/cm[sup.2] that was only 1/20 than that of Cr coating.