Structure and hardness of unbalanced magnetron sputtered TiBxNy thin films deposited at 500 °C

Thin films of TiBxNy with incorporation of different amounts of B into TiN0.81 were deposited on Si(100) at 500 °C using a reactive unbalanced dc magnetron sputtering in an Ar–N2 gas mixture. The structure and hardness were subsequently investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and microindentation measurements. Microstructure studies revealed that the structure, preferred orientation and mechanical behavior of present thin films strongly depended on their phase compositions in the Ti–B–N phase diagram. At a B contents below ∼ 12 at.%, the films with their compositions in the two-phase zone of TiN and TiB2, consisted of highly (111)-orientated nanocrystalline (nc-) TiN, accompanying with a small amount of TiB. As the B content was increased above ∼ 12 at.%, the film compositions shift to three-phase zone of TiN, TiB2 and BN, TiB gradually transformed to TiB2 and the films became nanocomposite structure of nc-TiN with mixed orientations embedded into amorphous (a-) matrices comprising TiB2 and BN. Simultaneously a swift change in preferred orientation of nanocrystallites from (111) to (200) occurred, accompanying with an obvious decrease of nanocolumn size, which is presumed to be contributed to change in film nanostructure from solid solution to nanocomposite at this B content. Incorporation or increase of B increased the hardness value. A hardness maximum of ∼ 48 GPa was observed at a B content of ∼ 9 at.%. A decrease of hardness value was followed with further increase of B content. The improved mechanical properties of TiBxNy films with incorporation of B into TiN were attributed to preferred orientation and phase composition. The residual stress was not consistent with the hardness, and increased with increase of B content, which was contributed to increase of amorphous matrices phase.