New understanding of hardening mechanism of TiN/SiN(x)-based nanocomposite films

In order to clarify the controversies of hardening mechanism for TiN/SiN(x)-based nanocomposite films, the microstructure and hardness for TiN/SiN(x )and TiAlN/SiN(x )nanocomposite films with different Si content were studied. With the increase of Si content, the crystallization degree for two series of films firstly increases and then decreases. The microstructural observations suggest that when SiN(x )interfacial phase reaches to a proper thickness, it can be crystallized between adjacent TiN or TiAlN nanocrystallites, which can coordinate misorientations between nanocrystallites and grow coherently with them, resulting in blocking of the dislocation motions and hardening of the film. The microstructure of TiN/SiN(x)-based nanocomposite film can be characterized as the nanocomposite structure with TiN-based nanocrystallites surrounded by crystallized SiN(x )interfacial phase, which can be denoted by nc-TiN/c-SiN(x )model ('c’ before SiN(x )means crystallized) and well explain the coexistence between nanocomposite structure and columnar growth structure within the TiN/SiN(x)-based film.