Effect of thermal cycles on optical properties of nanostructured coatings TiAlN/Cu

The change in the diffuse reflectance spectra of nanostructured TiAlN/Cu coatings after thermal cycling under conditions equivalent to 16 hours in near-earth space orbit has been studied. Thin-film TiAlN coatings with the addition of 7–8 % copper and with various Ti / Al ratios in the metallic component as well as between the metallic and non-metallic components of the solid solution were formed by reactive magnetron sputtering. It has been shown that the reflection in the spectral range of 500–2500 nm for samples with a higher titanium concentration is noticeably higher and increases after thermal loading, while for a sample with a lower titanium content, the reflection does not change. The solar absorption coefficient α s and the thermal emittance ε, as well as the α s / ε ratio, were calculated from the reflectance spectra. For samples with a predominant metallic component ((Ti + Al) / (N + C) = 1.3) and the Ti / Al ratio of 0.95, this ratio did not change after thermal cycling and amounted to 1.44. For samples with an increased titanium content (Ti / Al = 2.34) and an equimolar ratio of metallic and non-metallic components, the α s / ε value before thermal cycling was 3.82 and decreased to 3.65 after thermal loading. The band gap width and its change after thermal cycling were also calculated for both types of coatings. The physical processes occurring in TiAlN/Cu composites during thermal cycling are discussed based on optical spectroscopy data.