Browsing by Author "Liu, Xuejie"

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    Basic structure and formation mechanism of Ti-Si-N superhard nanocomposite coatings
    (2009) Liu, Xuejie; Westkämper, Engelbert (Univ.-Prof. Dr.-Ing. Prof. E.h. Dr.-Ing. E.h. Dr. h.c. mult.)
    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. 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 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. The ab inito calculations have been performed with VASP code. The basic structure and the formation mechanism of the Ti-Si-N composite coating have been identified. The total energy calculation results show that (a) there is no silicon interstitial solid solution in the TiN crystallite under the thermal equilibrium condition; (b) if a titanium atom or a nitrogen atom is missing in the TiN crystallite, a silicon atom is possible to occupy the vacant site and to form the substitutional solid solution; (c) the basic structure of the Ti-Si-N superhard composite coatings is the TiN crystallites with Si-4N-4Ti and Si-2N-2Ti in the boundaries.