Translated Abstract
Nanocomposite coatings have a great superority of industrial application in surface modification of tools and dies due to special properties such as compatible microstructure, excellent mechanical properties and favorable chemical stability. In this study, base on concept of design of superhard nanocomposite coatings, Ti-Si-N, Ti-Al-Si-N and Ti-Si-C-N nanocomposite coatings with beyond 40GPa hardness were deposited by plasma chemical vapor deposition (PCVD) and physical vapor deposition (PVD), phase’s composition, mechanical properties and thermal stability were discussed. The deposition processing for inner-surface of components with complex geometry was simulated. The tribological properties of superhard nanocomposite coatings under room and elevated temperature were systematically characterized. The progress was summarized as follows.(1) Based on PCVD system and its processing feature, the phase’s microstructure of Ti-Si-N coatings was mainly influenced by activity of N2. The relationship between nanostructure and mechanical properties was discussed. The universality rule that microstructure and chemical composition influence on their properties was summarized. The results showed that the change of phase composition was resulted from variable N2 activity. In Ti-Si-N system, the crystalline size keeps smaller than 10 nm. Generally, the hardness of Ti-Si-N coatings had a parabola function dependence on thickness of amorphous Si3N4. The hardness of coatings can achieved maximal value as TiN crystals are surrounded by one monolayer Si3N4. Meantime, the coating possessed excellent fracture toughness. The ability of corrosion resistance and oxidation resistance was increased with Si addition.(2) The influence of oxygen and chlorine contents in Ti-Si-N coatings on hardness was investigated. The results showed that the certain oxygen and chlorine contents can result a great decrease of the hardness of Ti-Si-N coatings prepared by PCVD. As oxygen content below 0.2 at.%, the hardness of coatings can reach 45-55GPa, but, the hardness decrease to 30GPa after oxygen content increase to 1-1.5 at.%. The hardness of Ti-Si-N coatings was controlled by hydrogen, oxygen and chlorine together. During PCVD processing, oxygen contents have a greater effect on hardness than chlorine contents, because oxygen and hydrogen result hydrolyze reaction of chloride and resultant accelerate hydrolyze reaction of Si3N4 and TiN.(3) The effect of annealing on crystalline size and hardness of nanocomposite coatings was investigated. Thermal diffusion between coating and substrate was also studied. The results showed that nanocomposite coatings possess a high thermal stability, crystalline size of as deposited coatings determined recrystal temperature. Thermal diffusion has some effects on thermal stability. It was concluded that high thermal stability of nanocomposite coatings result from spinodal decomposite in coatings.(4) Using blind holes of different diameter and deep, the deposition of Ti-Si-N coatings in complex-shaped caves of various tools was simulated. It was shown that dimensions of holes have an influence on uniformity and properties of coatings. The ability of pulsed PCVD on surface modification was evaluated. A model of deposition into complex-shaped caves was given.(5) Based on developing wear resistance and low friction coefficient coatings, Ti-Si-C-N coatings were prepared by PCVD. Detailed structural and chemical characterization suggest the formation of a Ti(C,N)/a-C/a-Si3N4/a-TiSi2 nanocomposite structure, and the crystalline size changed in range from 2nm to 25nm.. The round grain of Ti-Si-C-N containing low N contents changed into strip grain. Under certain processing parameters, the hardness of coatings had a linear increasing trend with increasing of Si and C contents and values of exceeding 40GPa have been achieved.(6) A comparative tribological behaviour investigation of Ti-Si-N and Ti-Si-C-N coatings with high hardness was carried out. The results showed that the wear resistance of Ti-Si-N coatings under room and elevated temperature was better than TiN coatings, but the friction coefficient of Ti-Si-N coatings under room temperature reached ＞ 0.5, just had a light decreasing under 550℃. Comparing with Ti-Si-N coatings, the friction coefficient of Ti-Si-N containing C contents decreased to below 0.3. The friction mechanism of Ti-Si-C-N coatings was controlled by a-Si3N4 contents in coatings.
Translated Keyword
[nanocomposite coatings hardness thermal stability tribology]
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