Titanium-boron-nitride (TiBN) coatings have attracted great attention for use in the machining industry owing to their elevated hardness at large temperatures as well as good wear and oxidation resistance and are therefore ideal candidates for high-speed cutting materials. Boron is known for strengthening effects in metallic alloys through grain refinement or segregation onto the grain boundary (GB). In TiN, however, the role of boron for GB behavior is still largely unclear. Density Functional Theory (DFT) calculations are able to provide crucial insights regarding the energetics and structure of solute segregation in representative GBs and are, therefore, of great value to complement experimental investigations on GB segregation.

We present DFT simulations of GB segregation of boron in TiN. We evaluate the segregation energy profile for substitutional boron in a Duffy-Tasker-type and Kingery-type GB of TiN, which are suggested to be the two most stable GB structures of TiN. Both Ti and N sites are considered as substitutional sites. Additionally, we analyze the energetic differences of segregation sites in terms of atomic parameters such as Bader charge analysis, atomic radii and bond order parameters. In order to verify the theoretical results we also present Atom Probe Tomography as well as Transmission Electron Microscopy measurements of TiBN coatings, which were created via Chemical Vapor Deposition for two specimen with 8 at.% and 25 at.% of boron, respectively. We compare the experimental results with DFT through a thermodynamic approach which allows to estimate solute concentrations on the grain boundary based on the calculated DFT segregation energies. With this, our results provide new insights regarding the role of boron for the design of high-performance TiN-based coatings.