Influence of carbon variation on the microstructure and hardness of CrTiAlCN coatings

This study investigates the effect of varied carbon content on the microstructure and mechanical behavior of CrTiAlCN coatings deposited on Si wafers using unbalanced magnetron sputtering in an argon (Ar), nitrogen (N₂) and acetylene (C₂H₂) gas mixture. In order to achieve varying carbon contents, coatings were deposited using different C₂H₂ flow rates. The structural, morphological, surface chemical binding states, nanostructure, and nanohardness of the CrTiAlCN coatings were analyzed using microstructural and mechanical characterizations. The results reveal that increasing carbon content considerably influences the microstructural evolution of the CrTiAlCN coatings, driving a transition from columnar morphology to a more compact and refined structure. Such densification enhances hardness, primarily due to lattice distortions caused by incorporated carbon atoms and the formation of stronger chemical bonds (e.g., Ti–C, Al–C). However, excessive carbon incorporation likely results in the formation of amorphous carbon-rich phases, which act as soft inclusions, thereby reducing nanohardness. These results underscore the importance of optimizing carbon content in CrTiAlCN coatings to achieve an optimal balance between microstructural integrity and mechanical performance, rendering them highly effective for advanced tool protection applications.