Effects of B content on microstructure and mechanical properties of nanocomposite Ti-B_x-N_y thin films

Thin films of Ti- Bx - Ny were deposited on Si(100) at room temperature by reactive unbalanced dc magnetron sputtering in an Ar- N2 gas mixture. The effects of B content on microstructure and mechanical properties of these films have been analyzed using x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, x-ray diffraction, transmission electron microscopy, atomic force microscopy, micro-indentation measurements, and an optical interference method. Microstructure studies revealed that depending upon the amount of B addition, the films showed two- or three-phase nanocomposite structure. At B contents below about 10 at. %, the films consisted of mainly TiN bondings with a small amount of TiB and BN bondings. As the B content increased, TiB gradually transformed to Ti B2 and the films consisted of nanocrystalline (nc-) TiN embedded in an amorphous (a-) Ti B2 matrix. A maximum hardness of ∼44 GPa was observed in a film with B content of 19 at. %. The improved mechanical properties of Ti- Bx - Ny films with the addition of B into TiN were attributed to their densified microstructure with development of fine grain size and different phase combination. The reduction in grain size has also been supported by means of a Monte Carlo simulation. When B contents reached ∼42 at. % or above, an amorphous-like nanocomposite of nc-TiNa-Ti B2 a-BN was formed. The effect of thin a-Ti B2 layer in stabilizing nc-TiN structure is also elucidated and explained on the basis of structural and thermodynamic stability. © 2005 American Vacuum Society.