Thermo-physical properties of coatings in the Ti(B,N) system grown by chemical vapor deposition
Hard protective coatings are commonly subjected to temperatures exceeding 1000 °C, which has significant influence on their thermo-physical properties and the associated performance in application. Within the present work, temperature dependent physical properties of coatings within the Ti(B,N) system grown by chemical vapor deposition were correlated with their chemical composition. High-energy X-ray diffraction experiments in inert atmosphere proved that TiN, TiB2 and ternary TiBxNy coatings with varying B contents are thermally stable up to 1000 °C. In-plane strains of TiN and TiBxNy coatings diminish during heating, whereas TiB2 exhibits compressive strain enhancement up to the deposition temperature. Nanocrystalline TiB2 exhibits more pronounced grain growth during annealing compared to coarse grained columnar TiN. Within the investigated coatings, the mean thermal expansion coefficient decreases as the B content increases. The same trend was observed for the thermal conductivity, which correlates with the grain size of the coatings.