Microstructure, Mechanical and Corrosion Properties of Column-Free CrNx Coatings Deposited by Closed Field Unbalanced Magnetron Sputtering

Abstract

CrNx coatings with a low nitrogen content below 31.7 at.% were deposited using closed field unbalanced magnetron sputtering by varying the N2:Ar flow ratio. A dense and column-free CrNx coating was obtained at a nitrogen content of 14.8 at.%, whereas the other CrNx coating were all columnar structured. The column-free CrNx 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 Cr2N nanocrystallines. The pinning effect of Cr2N nanocrystallines and point defects in Cr(N) grains are responsible for the formation of a column-free CrNx coating. The columnar-free CrNx coating exhibits a high hardness of 33.7 GPa, which is comparable to the hardness of Cr2N coating but 2.6 times larger than that of the Cr coating. It also has significantly better corrosion resistance than both Cr and Cr2N coating, with a corrosion current density of 4.1 × 1.0−9 A/cm2 that was only 1/20 than that of Cr coating.