Microstructure evolution of nc-TiN/a-(C, CN_x) nanocomposite films with different amorphous phase amounts

The microstructure evolution of two-phase nanocomposite Ti-C-N thin films grown by reactive close-field unbalanced magnetron sputtering in an Ar-N ₂ gas mixture with microstructures comprising of nanocrystalline (nc-) Ti(N,C) phase surrounded by amorphous (a-) (C,CN_x) matrix under different a-phase amounts have been investigated by using high-resolution transmission electron microscopy and Monte Carlo simulation. The results show that with the a-phase amounts increasing, the grain size decreasing and a size-dependent lognormal grain size distribution have been found in nanocomposite films. The formation mechanism of this microstructure evolution is attributed to the transformation of grain growth mode from the nc/nc-boundary-curvature-driven growth to the a/nc-boundary-curvature-driven growth accompanied with a convergence of energy on per grain boundary with grain size decreasing (i.e. a-phase amount increasing), leading to the tendency from the offlognormal size distribution to the lognormal one. When a-phase amount increases to about 28% with grain size reducing to let per grain boundary covered by one monolayer a-phase, the uniform diffusion-controlled growth is dominant, resulting in the lognormal grain size distribution. This study suggests an important implication to prepare the nanocomposite films with a well-controlled nanostructure. © 2013 The Authors. Published by Elsevier Ltd.