Effect of plasma nitriding and modulation structure on the adhesion and corrosion resistance of CrN/Cr2O3 coatings

Abstract

This paper examines the corrosion resistance of high-speed steel (HSS) substrates subjected to plasma-nitriding (PN) before being coated with CrN (in a single layer) or CrN/Cr2O3 (in multiple layers). Low-temperature (∼300 °C) nitriding treatment was applied for various durations (1 h, 3 h, and 5 h) with the aim of maximizing the adhesion strength and corrosion resistance of the HSS substrate. The multilayer coatings were applied in various thickness ratios of CrN vs Cr2O3 using high-power impulse magnetron sputtering (HiPIMS). The purpose of this study was to investigate the influence of plasma nitriding and Cr-based coating layers on the microstructural characteristics as well as the adhesion and corrosion characteristics. Specimens that underwent PN treatment for 5 h presented Lc1 and Lc2 values of 40.2 N and 78.9 N, respectively. The adhesion strength of the CrN/Cr2O3 multilayer coated PN-HSS substrate (PN-5h) (Lc 1 = 93.8 N) greatly exceeded that of the CrN-coated specimens. These results demonstrate that plasma nitriding and the modulation period strongly affect the adhesion strength between Cr-based coatings and the underlying HSS substrate. Corrosion resistance was characterized in terms of corrosion current, as follows: CrN/Cr2O3 multilayer > CrN layer > base-HSS. These findings also demonstrate that the application of a CrN/Cr2O3 multilayer coating can greatly enhance the corrosion resistance of HSS.