Investigation On The Microstructure, Mechanical Propetries And Tribologicat Behavior For NbN And NbC-based Thin Films

The important way to achieve environmental and social sustainable development is greenmanufacturing and remanufacturing. The low friction coefficient and wear resistant coatingdeposited by magnetron sputter deposition can be used to (i) improve the physicochemicalproperties on the surface of the parts,(ii) enhance the use performance for the parts,(iii) meet thespecial functional requirements,(iv) extend the service life and (v) achieve energy saving andconsumption reducing in equipment operation. The transition metal nitrides, carbides andcarbon-nitridehave attracted numerous attentions due to their excellent properties such as highhardness, the chemical inertness, high melting point and high conductivity. The combination ofthin film technology and nanotechnology cause the research upsurge in nano-composite film andnano-multilayer and these films exhibit outstanding properties. However, the understanding ofthe deposition method and the fundamental aspects of the growth of these films are still livingand challenging topics. Meanwhile, further investigations on other new system for understandingthe mechanisms of hardness enhancement for multilayer are very important. Relative tonanostructure film, the epitaxial film can be applied in microelectronics, optoelectronics industryand integrated circuit. And performing property measurements on well characterized single-phase epitaxial single crystal layers is an effective approach to deconvolute the intrinsicproperties from microstructural effects.Niobium carbide, niobium nitride and niobium carbon-nitride film exhibit excellentphysical and chemical properties suggesting a potential use in the extreme environments. In thisthesis, we investigated the relationship among the deposition parameter, microstructure andproperties for NbC and NbCN, and then deposited NbN/CNxand NbN/NbCN multilayer, andexplored the dependence of mechanical and tribology properties on modulation periodicity.Finally, we present the results of an investigation on the growth and physical properties ofepitaxial NbNxand NbCxNylayers deposited on MgO (001) by dc reactive magnetron sputtering.In Chapter2, the effects of substrate bias voltage (Vb), methane flow rate (FCH4) andsubstrate temperature (Ts) on the phase structure, composition, chemical bonding, morphology,stress, hardness and tribological behavior for NbC films had been explored. The microstructure,mechanical and tribological properties showed a significant dependency on carbon content.Varying the deposition parameter, accompanying with a phase transition from hexagonal-Nb2C to cubic-NbC, and at the highest carbon content, the film exhibits a typical nanocomposite structure consisting of NbC nanocrystallites embedded in an amorphous hydrocarbon (a-C:H) matrix.The best tribological behavior for the NbCx film obtained at68.7at.%carbon content in the film, which can be attributed to the presence of sp3-hybridized C-H bonding and formation of amorphous carbon.Although the nc-NbC/a-C exhibit the lower friction coefficient and the better wear resistant, its hardness is smaller than NbN film. Therefore, in Chapter3, we introduced the N and deposited the polycrystalline NbCN film, and hope the NbCN film keep the low friction coefficient and enhance the hardness.Increasing the nitrogen y in NbCxNy film0to1.01, the nitrogen was incorporated in solid solution Nb(C, N) grains but also facilitates an increasing amorphous C (N) matrix phase as well as a separate hexagonal NbN phase. The compressive stress, hardness, and elastic modulus are highest for the film with y=0.44, which also exhibits the lowest wear rate (H=42.1GPa,μ=0.19±0.02).NbN film shows the higher hardness but weaker tribological property, that is why we tried to deposit NbN based nano-multilayer, in order to enhance the strength, hardness and tribology at the same time. Under the optimized deposition parameter, we deposited the NbN/CNx and NbN/NbCN multilayer. Special for δ-NbN/CNx multilayer, when lCNx≥0.4nm, the multilayer has a mixture texture of NbN (200) and (111) with a good modulation periodic structure. The CNx layer is beneficial to relaxing the compressive stress induced by NbN layer. The obvious enhancement in hardness for multilayers is observed, whose maximum value approaches39.2GPa when lCNx=0.4nm,78%larger than that obtained by the rule of mixture value. The friction coefficient of NbN/CNx multilayers have a decrease trend with increasing the H/E ratio, but the poor wear resistance occurs as the H/E ratio is high, which can be attributed to the presence of a high stress.Polycrystalline NbN and NbCN layers have been attracting much attention, owing to their excellent characteristicssuch as high hardness. But the different microstructures in reported polycrystalline NbN and NbCN layers strongly affect the measured mechanical properties. Thus in Chapter5we present the results of an investigation on the growth and physical properties of epitaxial NbNx and NbCxNy layers deposited on MgO(001) by dc reactive magnetron. The layers grown at Ts=800-1000°C are epitaxial single crystals with a N/Nb ratio x=0.81-0.98thatdepends on Tsand causes a decrease in the relaxed lattice constant with increasing x from4.372-4.363. The layer that most closely corresponds to intrinsic NbN is grown at Ts=800°C, is anearly stoichiometric epitaxial NbN0.98(001) layer, and exhibits a hardness of19.5±0.5GPa andan elastic modulus of271±3GPa. While the hardness and elastic modulus of the best qualityepitaxial NbCxNylayers with x=0.38and y=0.65, deposited at Ts=1000°C, is24.9±0.8GPaand328±5GPa. These values are higher than the near stoichiometric epitaxial NbN0.98(100).