Microstructure and corrosion behavior of CrN and CrSiCN coatings

Three CrN-based coatings were deposited on 17-4PH stainless steel substrate using plasma enhanced magnetron sputtering (PEMS) technique. The microstructure and corrosion resistance were evaluated to examine the effect of Si and C in the coatings. The three coating compositions were CrN(Cr _0.69N _0.31), CrSiCN-1(Cr _0.55Si _0.014C _0.14N _0.3), and CrSiCN-2 (Cr _0.43Si _0.037C _0.24N _0.3). The testing results indicated that with the increase of Si concentration, the coating microstructure transformed from B1 structure to B1 + Si ₃N ₄ structure. All the three coating systems were subjected to electrochemical tests in 3.5% NaCl solution at room temperature. Potentiodynamic polarization results revealed that the CrSiCN-2 coating had a higher anodic current density and a lower corrosion potential when compared to the CrN and CrSiCN-1 coatings. Extended exposure in 3.5% NaCl caused several localized corrosion to the CrSiCN-2 coating due to the porous coating structure. Electrochemical impedance spectroscopic measurements demonstrated that the CrSiCN-1 has better corrosion resistance than CrN and CrSiCN-2.