| In mechanical and chemical engineerings, there are many different types of anti-friction and wear-resistant components with the hole surfaces as working surfaces, including drawing dies and varieties of components in fluid machineries(e.g., nozzles and valves). In applications such the hole surfaces may suffer severe wear and perform short lifetimes, constraining the improvement of the production efficiency and the quality of the productions. As a result, the stability and reliability of the relevant key equipments cannot be guaranteed in long-running operations. It’s a novel technology to develop and improve chemical vapor deposition(CVD) technology for diamond films growth on the hole surfaces, which can effectively prolong working lifetimes of the components, increase the production efficiency and improve the quality of the productions, meeting the requirements for the high reliability and long lifetimes put forward by the key equipments under the extremely harsh conditions. Nevertheless, it’s difficult to realize the mass production of high-quality and uniform CVD diamond films on hole surfaces of such the components, especially those with small and ultra-large apertures or complicated hole shapes. Besides, there are also some other problems limiting applications of CVD diamond films on hole surfaces, such as the poor adhesion and the low surface smoothness. Adopting the hot filament CVD(HFCVD) technology that is the most suitable for the mass production of diamond films on hole surfaces, researches in this dissertation are accomplished focusing on the problems needing solving, including the development of highperformance HFCVD diamond films, study on tribological properties of HFCVD diamond films, study on temperature and gas field distributions in HFCVD diamond films growth on hole surfaces, deposition and application of diamond films on different types of hole surfaces, which can be concluded as follows:1. Study on deposition and characterization of high-performance HFCVD diamond films. Firstly, the methane, acetone, methanol and ethanol are selected as typical carbon sources to discuss effects of the carbon source on the deposition and characterization of the pristine microcrystalline diamond(MCD) film, indicating that the diamond film with relatively high quality can be synthesized using the methane as the carbon source, but the acetone can provide relatively higher nucleation density, larger nuclei size and higher growth rate, as well as a certain film quality. Secondly, two novel composite diamond films are developed using the acetone which is beneficial for the nontoxic boron doping as the carbon source. The boron doped and undoped micro-crystalline composite diamond(BD-UCD) film performs favorable adhesion and extremely high surface hardness(nano hardness is 84.354 GPa), and the boron doped, undoped micro-crystalline and fine grained composite diamond(BD-UM-FGCD) film shows favorable adhesion, relatively low surface roughness(Ra value is 104.71 nm) and good surface processability, as well as relatively high surface hardness(nano hardness is 72.657 GPa).2. Study on erosive behaviors and mechanisms of HFCVD diamond films facing to the applications on hole surfaces. Erosive behaviors of diamond films are studied using an air-sand erosion rig and corresponding mechanisms are discussed with Hertz impact theory and so on. Erosive behaviors of diamond films deposited on different substrates are mainly related to their different film-substrate adhesions. Erosive behaviors of both the MCD and boron doped diamond(BDD) films approximately increase with the film thickness in the appropriate range, but the MCD film with excessively large thickness is easy to be removed. Moreover, the erosive behavior will also deteriorate when the film thickness approaches the depth of the highest shear stress. Comparisons between different diamond films present following results: Compared with the MCD film, boron doping can significantly improve the erosive behavior of the diamond film. The fine grained diamond(FGD) film has the worst erosive behavior. The BD-UM-FGCD film shows relatively good erosive behavior as a result of the good adhesion of the underlying BDD layer. Similarly, the BD-UCD film performs the best erosive behavior. When the erosion velocity ve=160 m/s and the erosion angle αe=30°, the steady-state erosion rate of the MCD film is 0.71 mg/kg, and its life is 110 min. The steady-state erosion rate of the BDD film is 0.62 mg/kg, and its life significantly increases to 215 min. The steady-state erosion rate of the FGD film is 0.74 mg/kg, and its life is only 95 min. The steady-state erosion rate of the BD-UCD film reduces to 0.57 mg/kg, and its life is 220 min. The steady-state erosion rate of the BDUM-FGCD film is 0.74 mg/kg, and its life also increases to 205 min. In addition, analyzed from the aspect of the carbon source, due to the higher film purity and less defects, the MCD film deposited with methane presents better erosive behavior.3. Study on friction and wear behaviors and mechanisms of HFCVD diamond films facing to applications on hole surfaces. Friction and wear behaviors of diamond films under both the experimental(ewb) and the simulated applied(awb) environments are studied, adopting a ballon-plate standard rotational frictional tester and a novel application wear test designed based on an inner-hole polishing apparatus, respectively. Comparisons between the different types of diamond films show the following results: Compared with the MCD film, boron doping technology can significantly improve the awb of the diamond film and increase its life under the simulated applied environment. The life of the FGD film is inferior to the else under the simulated applied environment, but it presents excellent ewb, manifesting as lower friction coefficient as compared with micro-sized diamond films when sliding against copper, aluminum, stainless steel, low-carbon steel and high-carbon steel. The BD-UM-FGCD film has both good ewb and excellent awb. Friction coefficients of BD-UM-FGCD films are much close to those of FGD films when sliding against mentioned metal materials, and their lives under the simulated applied environment are obviously elongated as compared with MCD and FGD films. The BD-UCD film also performs elongated life similar to the BD-UM-FGCD film, but its ewb is relatively poor, showing friction coefficients close to MCD films when sliding against commonly-used metal metals. Besides, from the aspect of the carbon source, the methaneMCD film presents much better ewb and awb. Moreover, combining the application wear test, detailed influences of the key deposition parameters on comprehensive properties of undoped diamond films deposited on circular hole surfaces with methane are further studied by the orthogonal tests. Accordingly, in order to optimize deposition parameters of different HFCVD diamond films on surfaces of different types of holes, a universal orthogonal experimental method is established, based on a Figure-of-Merit that takes into account the deposition efficiency, characterization and tribological properties of the diamond film.4. Study on physical field distributions in HFCVD diamond films growth on hole surfaces. Based on the finite volume method(FVM), a thermal-fluid coupled simulation model is established to clarify influences of deposition parameters, support cooling and heat transfer conditions on temperature and gas field distributions, considering the comprehensive effects of all the three heat transfer effects, including the thermal conduction, convection and radiation, providing sufficient theoretical basis for optimizing filament, fixture and other parameters related to temperature distributions, including the filament temperature, filament diameter, reactant gas flux, reactant pressure, arrangement of outlets and the shape of the red bronze block for fixing and cooling substrates. Besides, the substrate arrangement in the industrial apparatus is also optimized. The optimized substrate arrangement for the HFCVD equipment adopted for the mass production of diamond films on inner-hole surfaces is the combination of the triangular circular pattern and plates.5. Study on the fabrication and application of HFCVD diamond coated drawing dies. For all the circular-hole drawing dies with conventional, small or ultra-large apertures, BD-UMFGCD films are selected as protective coatings on hole working surfaces and basic deposition parameters are optimized by the universal orthogonal experimental method. A new deposition technology adopting a parallelogram filament tensioning device and an auxiliary heat transfer device is developed for the small aperture, and another deposition technology using a equilateral triangle filament arrangement is developed for the ultra-large aperture. FVM simulations are adopted to optimize detained filament and fixture parameters related to temperature distributions, and accordingly high-quality BD-UM-FGCD coated circular-hole drawing dies are produced and applied. As for shaped drawing dies(rectangular, tile or sector holes), BDD films with relatively lower residual stress and much better adhesion are chosen as protective coatings on hole surfaces and basic deposition parameters are optimized by the universal orthogonal experimental method. Moreover, filament arrangements adaptive to hole shapes are developed, and simulations designed by the orthogonal collocation method(OCM) are conducted to optimize specific filament and fixture parameters related to the temperature distribution, based on which high-quality BDD coated shaped drawing dies are produced and put into practice. Generally speaking, chosen diamond films can elongate working lifetimes of drawing dies, improve the production efficiency, reduce the material and energy consuming, guarantee surface quality, dimension precision and overall performance of productions. In summary, chosen diamond films can increase working lifetimes of typical drawing dies with conventional, small, ultra-large apertures and complicated hole shapes by factors of 10, 20, 20, 8 times, respectively.6. Study on applications of HFCVD diamond films on hole surfaces of erosive wear resistant components. Working conditions of the spray drying equipment put forward extremely high requirements for the erosive performance, but relatively lower requirements for the surface smoothness of hole surfaces of nozzles. Consequently, Si C is selected as the substrate due to its favorable adhesive strength to the diamond film, and BD-UCD films are selected as protective coatings. Due to the complexity of the hole shape, a two-step deposition approach is proposed to deposit high-quality BD-UCD films firstly on the hole surface and then the conical surface, adopting deposition parameters optimized by the universal orthogonal experimental method and the OCM simulations. The BD-UCD coated nozzle exhibits an apparent increase in the erosive resistance and the working lifetime(above five times as compared with the uncoated nozzle). Moreover, productions yielded with the BD-UCD coated nozzle have more stable quality than those produced with the uncoated Si C one. The structural optimization and design of the erosive wear resistant relief valve in the coal liquefaction equipment are accomplished by simulations. Afterwards, WC-Co material with favorable toughness is chosen as the substrate, and the low-cost methane-MCD film, which requires relatively simple deposition technology, is preferably deposited on the hole surface of the valve seat, which can provide sufficient protective effects, manifesting as improving the erosive behavior of the valve seat and prolonging the working lifetime and stability of the whole relief valve. |
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