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R Hahn, S. Rosenecker, T. Wojcik, O Hunold, S. Kolozsvári, H. Riedl:
"Microstructural influences on the fracture properties of CrN coatings";
Poster: 47th International Conference on Metallurgical Coatings and Thin Films, ICMCTF, San Diego, CA, USA; 2021-04-26 - 2021-04-30.

Transition Metal Nitrides (TMN) are well known for their good mechanical stability, chemical inertness, as well as tribological properties. Hence, they successfully found application in the metal forming industry, and are in use as protective coatings in the automotive and aerospace industry. Besides TiN, CrN is one of the most used and best investigated hard coatings, preferably applied in conditions that require a low coefficient of friction. A decisive disadvantage of these hard coatings, however, is their low fracture tolerance. Premature failure of the coating due to crack initiation and propagation leads to economic disadvantages or completely excludes an application. In recent years, micromechanical testing methods have made it possible to measure and specifically improve precisely fracture toughness of thin film materials. There are various methods known for measuring KIC obtaining all advantages and drawbacks, especially with respect to intrinsic material characteristics and accuracy.
In this contribution, we perform distinct micromechanical tests on cathodic arc evaporated CrN coatings. These coatings were deposited with different bias voltages and deposition temperatures in order to obtain a variation in both, microstructure (specifically crystallite size) and defect density. The importance of the microstructure on fracture characteristics has recently shown by Ast et al. for Ti-Al-N deposited by diverse PVD techniques [1]. However, a clear correlation between the column size and the density of column boundaries is still missing.
We found a significant influence of the residual stress state on the fracture properties of such hard coatings using the indentation fracture method. Furthermore, we used pillar splitting and cantilever bending tests to determine the intrinsic fracture toughness of our coatings with respect to the microstructure and defect density. These results were complemented by HR-TEM investigations together with x-ray diffraction studies, and nanoindentation tests.

References
[1] Ast J., et al., (2019). Fracture toughness determination of arc-PVD and HiPIMS hard coatings by micro-cantilever and pillar splitting tests.

Fracture toughness, PVD, Coating

Project Head Helmut Riedl:
CDL-SEC