Basic structure and formation mechanism of Ti-Si-N superhard nanocomposite coatings

With the concept of digital factory, a research including experiment, kinetic Monte Carlo simulation, and ab initio calculation has been conducted to investigate the basic structure and the formation mechanism of Ti-Si-N superhard nanocomposite coatings. In sputtering PVD process, ion mass spectra and deposition rates have been measured. The measurement results show that the Ti-Si-N deposition in the sputtering PVD is a complicated process and it is difficult to obtain the stoichiometry of TiN without the measurement in situ. The experiments of the Ti-Si-N deposition demonstrate that Si addition obviously influences the film microstructure and hardness. But the atomic structure and the formation mechanism of the Ti-Si-N coatings have not been identified by the experiments. This indicates that the atomic simulation and calculation is necessary. Two kinetic Monte Carlo (KMC) simulation codes with the lattice model and with the off-lattice model have been developed. In the off-lattice KMC simulation, the dimer method was used to search the saddle points on the potential energy surface (PES), which provided the direct calculation method of activation energy and the relaxation algorithm of adatoms, so that this off-lattice KMC simulation is much closer to the real situation. But by the off-lattice KMC simulation, the basic structure and the formation mechanism of TiSi-N films have not been found out due to the inaccurate potential algorithm. Therefore, the ab inito calculation is needed. The ab inito calculations have been performed with VASP code which is based on density functional theory.The basic structure and the formation mechanism of the Ti-Si-N composite coating have been identified through the ab intio calculations. The total energy calculation results of the configurations of Si addition into the TiN crystallite or into the boundary of TiN show that (a) there is no silicon interstitial solid solution in the TiN crystallite under the thermal equilibrium condition; (b) if a