Microstructure and Surface Topography Study of Nanolayered TiAlN/CrN Hard Coating

The microstructure and surface topography of PVD hard coatings are among the most importantproperties, as they significantly determine their mechanical, tribological and other properties.In this study, we systematically analyzed the microstructure and topography of a TiAlN/CrNnanolayer coating (NL-TiAlN/CrN), not only because such coatings possess better mechanical andtribological properties than TiAlN and CrN monolayer coatings, mainly because the contours of theindividual layers, in the cross-sectional STEM or SEM images of such coatings, make it easier to followtopographic and microstructural changes that occurred during its growth. We investigated theeffects o f t he s ubstrate r otation modes o n t he microstructure a nd s urface topography o f t heNL-TiAlN/CrN coating, as well as on the periodicity of the nanolayer structure. The influence of thesubstrate material and the ion etching methods were also studied, while special attention was givento the interlayer roughness and influence of non-metallic inclusions in the steel substrates on thegrowth of the coating. The t opographical f eatures o f the N L-TiAlN/CrN coating surface are correlatedw ith t he o bservations f rom t he c ross-sectional TEM and FIB analysis. Selected non-metallicinclusions, covered by the NL-TiAlN/CrN coating, were prepared for SEM and STEM analyses by thefocused ion beam. The same inclusions were analyzed prior to and after deposition. We found thatsubstrate rotation modes substantially influence the microstructure, surface topography and periodicityof the NL-TiAlN/CrN layer. Non-metallic inclusions in the substrates cause the formation ofshallow craters or protrusions, depending on their net removal rates during the substrate pretreatment(polishing and ion etching), as compared to the matrix.