||This research is focused on the effects of various O２/N2 gas flow on the CrN and Cr (N, O)/CrN coating properties using cathodic arc ion plating technology. With X-ray and TEM, column structures were found in the CrN coating layer microstructures, which include CrN and Cr2N. Contrastingly, there were CrN, Cr2O3, and other compounds in the Cr (N, O)/CrN duplex coating layer. Upon analysis, we found oxidation of CrN and Cr2O3 phase formation on surface at the temperature of 600℃. At around 800C, there were formation Cr3C2 and Cr2O3 particles on the coating surface as seen by the SEM and AES.
Generally, cathodic arc ion plating will produce micro-particles. However, excess oxygen flow will accelerate the target poisoning resulting in increased micro-particles and voids. Our result indicates that this phenomenon occurs when there is/are increased oxygen flow and/or increased deposition time.
Upon analysis by Vickers and nano-indenter hardness test, we found the Cr (N, O)/CrN duplex coating layer has higher hardness than CrN coating layer because of its microstructure and residual stress. CrN has excellent adhesion, however, as oxygen flow increases, the adhesion of Cr (N, O)/CrN duplex coating layer decreases. This phenomenon occurs because of high hardness, low expansion coefficient, low toughness, and high residual stress of the Cr (N, O)/CrN duplex coating layer.
After calculating for the Young’s modulus (E), we found that as the value of the Hardness/Young’s modulus (H/E) ratio increases, the residual strain decreases, resulting in better wear resistance. After addition of oxygen, not only the nano-indenter hardness increases, but all of the Cr (N, O)/CrN duplex coating also have higher H/E ratio than CrN coating. High H/E ratio indicates lower plastic strains in the Cr (N, O)/CrN duplex coating; therefore, the production of chromium oxide on the surface will help the wear properties of the coating layer. Moreover, the erosion results show that both the CrN coating layer and Cr (N,O)/CrN duplex coating layer has high erosion resistance for low angle (30°), but low erosion resistance for large angle. If one can increase the adhesion, hardness, and toughness of the coating layer, then one can effectively increase the coating layer’s erosion resistance.
Results from the polarization test, alkali/acidic solution dipping test, and the salt spraying test indicates that the Cr (N, O)/CrN duplex coating layer has higher anti-corrosive properties than the CrN layer. For A356 aluminum emersion test, Cr (N, O)/CrN duplex coating layer has better anti-corrosive property because of its duplex layer microstructure. The specific microstructures of Cr (N, O)/CrN duplex coating layer decrease the probability of molten aluminum filtration into the substrate.