[Back]

R Hahn, M. Bartosik, A. Tymoszuk, P. Polcik, M. Arndt, P.H. Mayrhofer:
"Effect of Boron on the Mechanical Properties, especially Fracture Toughness, of TiN";
Talk: 45th International Conference on Metallurgical Coatings and Thin Films (ICMCTF) 2018, San Diego, CA; 04-23-2018 - 04-27-2018; in: "International Conference on Metallurgical Coatings Thin Films - Book of Abstracts", (2018), 2.

Titanium Nitride (TiN) thin films pioneered the application of ceramic hard coatings on tool materials for improving the wear resistance and consequently tool lifetime. The enhancement in wear resistance strongly depends on the mechanical properties of the coating, which can be further increased by alloying strategies. Here, we present the effect of boron alloying to TiN hard coatings on their mechanical properties, with a focus on the fracture toughness (KIC).
Thin films with different boron contents, ranging from 0.5 to 25 at%, were deposited using reactive, as well as non-reactive, unbalanced magnetron sputtering. The boron content and bonding characteristics (different types of B-bonds) were analysed by X-ray photoelectron spectroscopy and complemented by X-ray diffraction experiments to gather information on the structure of our hard coatings. The experiments unveil a clear increase in B-N-typed bonds with increasing boron content, resulting in a transition from fine-grained single-phase Ti(B)N (up to a B content of around 5 at%) to nanocrystalline two-phase Ti(B)N-BN structures (for contents >5 at%).
Micromechanical experiments ¬¬¬¬¬¬¬¬¬-conventional nanoindentation as well as fracture experiments- reveal hardnesses of up to 32 GPa and fracture toughness values of up to 11 MPa√m (both values include the influence of pronounced residual stresses in the coatings on Si (100) substrates) for boron contents of up to 5 at%. Higher boron contents resulted in a decrease in fracture toughness, hardness, and indentation modulus. We envision a soft, X-ray amorphous BN phase surrounding nanocrystalline TiN grains, to be responsible for this behaviour.
Based on our results we can conclude that B alloying has the potential to boost the mechanical properties of nitride based hard coating materials but only when softer BN phases are avoided, which can be controlled by carefully adapting the deposition parameters.