Effect of phase and elemental composition, structure, and texture of multilayer coatings based on TiCN and TiNbCN on the electrochemical behavior of high-speed steel in 3% NaCl solution

Abstract

Thin multilayer TiCN and TiNbCN coatings were obtained on a high-speed steel M2 by pulsed magnetron sputtering. The content of N2 and CH4 in the gas mixture was changed to obtain nanostructured layers with different phase and elemental compositions, structure, and texture. The microstructure, defects, and elemental composition of the coatings were investigated using an Ultra 55 field emission electron microscope with an EDX microanalysis system. The phase composition and texture of the coatings were determined using a Shimadzu XRD-6000 X-ray diffractometer with Cu-Kα radiation. Voltammetry and impedance spectroscopy on the coated samples were performed in a 3% NaCl solution. The corrosion behavior of the coatings was characterized by the corrosion current density and polarization resistance (at the corrosion potential). It is shown that the investigated coatings are electrochemically active, and corrosion processes occur not only on the substrate in the discontinuities of the coating but also on the surface of the coating. The TiN-TiCN-TiCN multilayer coating with a maximum content of the three-component phase TiC0.496N0.502, a minimum content of the carbide phase TiC, a maximum texture coefficient, a minimum crystallite size, lower internal stresses and deformations of the crystal lattice has the lowest corrosion current density 0.75 µA cm−2 among the investigated coatings. Niobium improves corrosion resistance, but the presence of a significant amount of the TiC carbide phase in the TiNbCN coating reduces this effect. The morphology of the coating surface after the electrochemical test was studied. The maximum damage of the surface layer is observed for the multilayer TiCN (1) coating.