Diffusion of Fe, Cr, and C in arc evaporated TiN and Ti-Al-N coatings and the influence on microstructure and hardness

Abstract

TiN and Ti-Al-N are highly valued as protective coatings for cutting tools due to their excellent properties like high hardness, oxidation resistance, and thermal stability. Even though numerous studies deal with the thermal stability and oxidation behavior of such coatings, only limited information about the element transfer during machining and its influence on the coating properties is available. As temperatures of more than 1000 °C are common, not only wear and oxidation but also transfer-material-diffusion between coated tool and workpiece can be detrimental. Therefore, thin films of Fe, Cr, and C- which are common transfer elements during machining- were deposited on cathodic arc evaporated TiN and Ti-Al-N coatings and subsequently vacuum annealed for 30 min at 600, 800, and 1000 °C. The concentration-depth profiles, obtained by cross-sectional EDX line-scans, clearly show significantly higher diffusion of Fe, Cr, and C into Ti-Al-N than into TiN. Additional annealing treatments at 600 °C are conducted for 10, 100, and 1000 min to study low temperature diffusion in more detail. The effect of the diffusion processes on microstructure and mechanical properties of TiN and Ti-Al-N is studied by X-ray diffraction and nanoindentation. We envision that the significantly different diffusion coefficients in TiN and Ti-Al-N have not only a pronounced influence on microstructure and hardness but also on the wear behavior of these coatings.