Determination of the efficiency of using multilayer CrN/MoN ceramic coatings for protection against hydrogen absorption and exposure to aggressive environments

The main objective of this study is to determine the prospects for using multilayer CrN/MoN ceramic coatings as protective sacrificial coatings providing increased resistance of steels to the complex destructive effects of hydrogen and aggressive environments due to the synergistic effect of alternating nitride layers and the formation of a dense, defect-resistant structure with highly effective diffusion barriers that restrain the diffusion of atomic hydrogen deep into the materials. The influence of hydrogenation processes on the wear and corrosion of the coating surface was determined using the scanning electron microscopy method, which was used to visualize surface defects formed as a result of external influences. Based on the data obtained, an analysis of the resistance of the coatings to degradation was conducted, and the role of the coatings in restraining destruction to wear and corrosion processes was determined. Moreover, it was found that increasing the number of layers from 4 to 20 inhibits degradation of strength properties by more than 2.2 times. Such changes in coating hardness and wear resistance are due to the barrier effect associated with the increased number of layers in the coating, which inhibits hydrogen diffusion into the coating. Tests of the resistance of samples after hydrogenation to an aggressive environment showed that the decrease in resistance to aggressive environments for coatings subjected to hydrogenation is most pronounced for samples subjected to hydrogenation for 100 h. In this case, the reduction in wear resistance (friction coefficient) is more than 1.5 to 2 times for coating samples subjected to hydrogenation compared to the original samples. According to an assessment of changes in the adhesive strength of coating samples after exposure to an aggressive environment, it was found that in the case of the original samples (not subjected to hydrogenation), an increase in the number of layers from 4 to 20 leads to a decrease in surface delamination from 1.51% to 0.95%. Moreover, for samples subjected to hydrogenation for 100 h, in the case of 4-layer coatings, the change in adhesion strength is more than 11.4%, and in the case of 20-layer coatings, the decrease in adhesion strength is approximately 6.9%, which is more than 1.5 times lower. The novelty of the study lies in determining the role of variation in the number of layers on resistance to degradation processes caused by hydrogenation and subsequent exposure to an aggressive environment, as well as determining the mechanisms of restraint due to variation in the number of layers and the barrier effects they create, which slow down the degradation processes of mechanical and strength properties.