The duplex treatment of AISI 420 steel samples by nitriding in a radiofrequency inductively coupled plasma (RF-ICP) discharge of Ar + N2 + H2 atmosphere followed by CrAlN coating deposition was performed in this study. The influence of plasma nitriding (PN) duration (10, 20, 40, and 60 min) on the structural and functional properties of the duplex-treated samples was determined. A non-linear dependence of AISI 420 steel nitriding kinetics was found on the square root of the PN duration. The thicknesses of the compound layer (CL) and nitrogen diffusion zone (DZ) in the samples and their phase composition resulted in different critical loads of coating failures under adhesion tests. Increasing the load-bearing capacity by the PN caused coating hardening in duplex-treated samples. The role of the PN duration on the wear characteristics of the AISI 420 steel samples after the duplex treatment has been discussed. Corrosion tests of AISI 420 steel demonstrated the significant enhancement (5–67 times) of its corrosion resistance in a 3.5 wt.% NaCl solution after duplex treatment.

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