Microstructure and properties of Cr-Cu-N coatings with ultra-low copper content

Abstract CrN and Cr–Cu–N coatings were deposited under different bias by RF magnetron reactive sputtering. The Cr–Cu–N coatings with an ultra-low Cu content of 0.53–2.1 at.% were prepared. The influence of Cu content and substrate bias on microstructure and hardness was investigated. With increasing bias both CrN and Cr–Cu–N coatings change the preferred orientation from (220) to (111), then to coexist of (111) and (200), finally to (111), and the grain refining effect is obvious. The addition of Cu is more conductive to the strengthening of CrN(111), but cannot cause an obvious decrease in the grain size. All the coating surfaces present nearly feature-less characteristic, implying a fine grain microstructure. The hardness decreases as the bias increases. The Cr–Cu–N coating containing the maximum soft metal of Cu (2.1 at.%) has the highest hardness of 27.1 GPa due to a dense structure, smoother surfaces, and the highest degree of Cu coverage. The reason of failure to get superhard Cr–Cu–N coatings is a combination of incomplete monolayer coverage due to ultra-low Cu content, (220) preferred orientation, and the grain size of CrN with less than 20 nm.