The sample can be visualized as a two-layered structure, namely a substrate with a coating on top, where the main contribution to the measured reflectance is due to diffuse reflection at the substrate-coating boundary, but is decreased by attenuation within the coating on top of the substrate, both before and after reaching the coating-substrate boundary.
The membrane suspension was then adjusted to 0.60 ± 0.05 mg/mL, 5 mL/column, in order to make an excess membrane suspension for reaching the maximum coating content.
The critical energy release rate for propagation in the bond coat is considerably smaller so that most vertical cracks can be expected to stop upon reaching the bond coat.
This complete microcharacterization of the multilayered Ti TiN/CNx systems coupled with the observed adhesion properties has allowed to identify relationships between the deposition conditions and the material chemistry and structure, in order to reach the desired coating performance.
Up to 700 °C no indentation induced cracking occurred in the titanium rich coating, however, reaching the annealing temperature of 1000 °C, this coating became porous and spontaneous tensile cracking appeared on its surface.
Indeed the surfaces that could be coated are only limited by the temperature reached during the coating process (approx 150°C) substrates would have to withstand this temperature.
In the case of thin layers, shorter wavelengths can reach through the coating layer to the reflective substrate, while for thicker layers this can only happen at longer wavelengths.
As the content of FeCr was 12 wt%, the hardness of the coating reached the highest value, 1027 HV, and the wear resistance was about 3 times the substrate, 2 times the coating without ferrochromium addition.
It is also shown that the density of cracks that reach the surface of the coating depends only on the thickness of the outer Zn-rich layers of the coating that act as barriers to crack propagation.
The corrosive species such as Cl−, SO4 2− or O2 are prone to intrude into the coating, reach the surface and initiate the localized corrosion.
Although the microstructures reveal pores, they are not critical for corrosion resistance because they are small and shallow and do not penetrate deep enough to reach the interface substrate-coating.
