| Currently, a large number of parts used in military are still prepared by die steels such as Crl2MoV. However, the requirements of the parts’performance are upgrading with the increasing complexity of the service environment for military weapons and the rapid development of modern manufacturing. The Cr12MoV components have not been able to meet the complex environment, so surface treatments become necessary way. In recently years, with the development of machining industries towards rapid and continuous processing of complex and small-scale materials, surface treatments as hard film, coating (less than10um) have been common methods for improving the service performance of the parts. Through the processing, parts’strength, toughness and wear resistance have been improved, and the service life of components is also improved. At present, the traditional hard films can no longer meet the requirement for the surface treatment of steel substrates due to the demand of better comprehensive performance (anti-corrosion, anti-wear, especially self-lubricating), so preparation of new composite films becomes important problems to be solved in this field.Diamond-like carbon (DLC) film shows low friction coefficient, high hardness, wear resistance, and could be the first choice for surface modification of Cr12MoV steels. However, the application of DLC film has been restricted by the low thermal stability and low adhesion strength with steel-base materials. Moreover, the TaN film in relevant research shows high corrosion resistance, hardness, thermal stability, and low friction coefficient, demonstrating the prospect as hard wear-resistant and bearing layer of composite DLC film. This paper aimed to design and prepare DLC films composited with TaxMe1-xN multilayer films to match Cr12MoV steels, in order to improve comprehensive performance of the film. In this paper, DLC/TaxMe1-xN were prepared by PSII, MW-ECR MS and CVD, following the order of TaxMe1-xN'TaxMe1-xN multilayer'DLC/TaxMe1-xN multilayer. The functional graded DLC films improved the employ life of substrates by the lubrication. And the system also could keep the wear resistance of the system with a lower friction coefficient when the DLC layer failed under the increasing loads, for preventing the failure of parts due to a sudden increase of the friction coefficient. The film met the performance modification requirement of Crl2MoV. The contents of this thesis are divided into sections as follows: (1) First, on the basis of plasma density variation in the deposition system, several groups of TaN films were prepared on Cr12MoV substrate using MW-ECR enhanced magnetron sputtering by controlling the process parameters. It focused on the influence of temperature, pressure, and bias on the structure and properties of TaN films, and the influence mechanism of different factors on film mechanical properties was discussed. TaN film exhibited hexagonal structure, and the coefficient of friction was less than0.2. The film hardness, modulus increased with increasing preparing temperature, the film hardness deposited under573K was39.36GPa, but the oxidation was found while the film was heat treatment in lower vacuum; The film hardness and modulus decreased with the increasing pressure; the values increased with the increase of bias, reached the maximum value at-100V, then decreased. Integrated consideration of different factors, it was found preparing temperature, pressure, and bias affect the ion energy and the quality of the interface between coating and substrate in the thin film nucleation and growth, resulting in the change of film properties. The mechanical properties and wear resistance of film attained the best value under lower preparing temperature, with pressure of0.1Pa, Ar/N2ratio of4.5/1, pulse bias voltage of-100V.(2) Transition metals of Ti and Cr were added into TaN films, the influence of doping amount on the TaxMe1-xN film structure and performance were investigated. The influence mechanism of doped second particle on film mechanical properties was also discussed. The structure of composite TaxMe1-xN film transited from hexagonal to cubic; When the Ti/Ti+Ta ratio reached0.43, the hardness of Ta0.57Ti0.43N film reached the maximum value of33±2GPa, adhesion strength reached27GPa; When Cr/Cr+Ta ratio was0.61, the Ta0.39Cr0.61N film showed the maximum hardness of30±1.5GPa, adhesion strength of29N; the friction coefficient increased from0.2to0.4with the increase of Ti, Cr contents. It was found that doped proper Ti, Cr into TaN film is in favor of film nucleation, reduction of grain size, and solid solution strengthen, resulting in the improvement of film properties。(3) The multilayer structure of TaN/Ta、TaxMe1-xN/Me、TaxMe1-xN/MeN/Me films were prepared on the basis of the TaN and TaxMe1-xN deposition. The strength mechanism of soft/hard multilayer structure on bonding strength was analyzed. TaN/Ta multilayer films with modulation thickness around250nm showed the best mechanical properties, hardness was26～27GPa, adhesion strength was around36N, wear resistance significantly increased; Compared to the monolayer TaxMe1-xN film, the wear resistance and bonding strength of TaxMe1-xN/Me、TaxMe1-xN/MeN/Me multilayer films were improved by the multilayer structure, the adhesion strength increased up to50N, the wear resistance was significantly improved. It was found that soft/hard structure with appropriate modulation period effectively relieve the film stress, and prevent crack propagation in the brittle layer, resulting in the improvement of the wear-resistance and adhesion strength. (4) The influence of bombardment and injection on the properties of TaN film was discussed, and the TaN/Ta film was prepared by multilayer injection for the first time. The surface roughness of substrate increased with the increase of uniform mountain-like structure by high-energy Ar ion bombardment processing. After the deposition of TaN film, the uniformity and compactness of surface were significantly improved, the adhesion strength increased up to30N; The TaN film on the substrate injected with Ta and TaN at16kV bias showed better adhesion strength, which was up to36N; multilayer injected TaN/Ta films with Ta showed better adhesion strength up to55N. It was found the substrate surface area increased with increasing energy of Ar ion bombardment, which improved the shear resistance at the interface, resulting in the improvement of adhesion; Amorphous diffusion zone formed by implantation of Ta reduced the interfacial energy, leading to the improvement of interface quality; The adhesion strength of multilayer injected TaN/Ta were improved due to the formation of more diffusion zones between the TaN/Ta interfaces, meanwhile, the soft layer resulted in the reduction of stress due to the characteristics of shear bands.(5) MW-ECR magnetron sputtering and chemical vapor deposition were used to prepare DLC films and DLC lubrication films, and the lubrication mechanism was also analyzed. It was found the friction coefficient of DLC film was reduced by doping MoS2in the amorphous DLC network. When C current was1.5A, MoS2current0.3A, the friction coefficient attained the lowest value of0.074, and the hardness was around14GPa. It was found that the MoS2dispersed in the amorphous DLC influenced on the mechanical properties and friction coefficient of DLC film. The Mo/S ratio and sp3contents could be changed by the sputtering energy and bias, for changing the C-C, C-H, and S-H bond, resulting in the balance of the mechanical properties and lubricity of films.(6) MW-ECR enhanced sputtering, chemical deposition, and implantation were used to prepare multilayer DLC/TaxMe1-xN functional gradient multilayer lubricant films. Compared to the DLC film without support layer, the wear resistance was significantly improved up to4times, adhesion was increased up to5-10times. The DLC film showed lower friction coefficient under1N; when the DLC lubricant layer failed under higher load (3N,400r/min), the nitride bearing layer played wear-resisted role, friction coefficient of DLC/TaN/Ta system was still lower than0.15after the failure of DLC layer, maintaining the stability of system. |
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