Microstructure and corrosion behavior of duplex coating fabricated by plasma nitriding and TiN/TiCN pulsed DC PACVD method on K390 MC cold work tool steel

The paper compares the corrosion resistance of the TiN/TiCN coatings applied to samples of hardened and tempered tool steel for cold work grade K390 MC in relation to the plasma nitrided and non-coated samples. The multilayer coating of the TiN/TiCN is produced by a plasma-assisted chemical deposition from the vapor phase (PACVD) in industrial furnaces with hot wall. Plasma nitriding is performed in the same furnace in a separate cycle. Corrosion tests for determining the density of corrosion current, corrosion potential and corrosion rate were carried out using electrochemical polarization in aqueous 3.5% NaCl. Investigation of factors affecting coating’s corrosion resistance included testing of surface roughness before and after deposition, testing of chemical composition and structure of the coating. The microstructure and chemical composition of the coatings were examined by scanning electron microscopy (SEM). The results showing the increasing of the corrosion resistance of the TiN/TiCN coating three times in comparison with non-coated samples and the samples were plasma nitrided without a compound layer. The multilayer TiN/TiCN coating corrodes with a pitting corrosion, while non-coated and plasma nitrided samples corrode with local and general corrosion.