Structural evolution and electrochemical behaviors of multilayer Al-Cr-Si-N coatings

The corrosion behaviors in 3.5% NaCl and 10% H2SO4 solutions of the nano-composite Al-Cr-Si-N coatings, deposited on stainless steel 316L substrates using multi-arc ion plating process, annealed at 700 °C, 800 °C and 900 °C, each for 2 h, was studied. The phase structures, surface morphologies, adhesion strength, and corrosion properties of the Al-Cr-Si-N coatings before and after vacuum annealing were investigated. Results indicated that, with increasing annealing temperature, the phase structures of the nano-composite Al-Cr-Si-N coatings varied from solid solution (Cr,Al)N phase to CrN, Cr2N and AlN phases with a hexagonal close packed structure (hcp-AlN), and then to CrN, Cr2N, hcp-AlN and Cr phases, and finally to CrN, Cr2N, hcp-AlN, Cr and σ-FeCr phases. The defects on the coating surface were decreased simultaneously. The samples annealed at 800 °C had the highest adhesion strength. The potentiodynamic polarisation measurements showed that the corrosion resistance of coatings was improved after annealing. The coatings annealed at 800 °C had the best corrosion resistance in 3.5% NaCl solution, and the coatings annealed at 700 °C had the best corrosion resistance in 10% H2SO4 solution.