Bias-enhanced Hot Filament Chemical Vapor Research Articles

Study of Tribological Properties of Textured Boron-Doped Diamond Film under Water Lubrication

To explore the effects of different surface textures and boron doping on the surface friction properties of diamond film, cemented carbide tools were provided with elliptical and groove textures using laser technology. Undoped diamond (UDD), boron-doped un-textured diamond (BDUTD), boron-doped elliptical textured diamond (BDETD), and boron-doped grooved textured diamond (BDGTD) films were prepared by bias-enhanced hot filament chemical vapor deposition (BEHFCVD). The effects of different surface texture and lubrication conditions on the tribological properties of diamond coated tools were studied by TBT-M5000 ball-on-disk friction tester. The surface morphology, film quality, adhesion strength and residual material composition of diamond films were characterized by SEM, Raman, Rockwell hardness tester and EDS, respectively. The results show that boron-doped can effectively improve the film quality and the existence of texture further improves the adhesion strength of diamond film. Under water lubricated condition, the average friction coefficients of UDD and BDGTD film are 0.1426 and 0.123, respectively. The wear rate of the steel ball corresponding to BDGTD film shows excellent anti-friction performance, which is 1.37 × 10−8 mm3 / Nm. From the wear morphology, the UDD film pair has the largest wear diameter, which is 1.536 mm. The steel ball corresponding to BDGTD film has the smallest wear diameter, which is 1.258 mm. Compared with the other three films, the wear of UDD film is the most serious and BDGTD film shows the best wear morphology, this is due to the fact that texture can promote the lubricant to enter the friction contact surface, make the contact surface fully lubricated and can collect wear debris.

Tribological behavior and cutting performance of monolayer, bilayer and multilayer diamond coated milling tools in machining of zirconia ceramics

In this work, a comparative study of diamond films consisting of alternate microcrystalline (MCD) and nanocrystalline diamond (NCD) layers is conducted. Diamond films including monolayer, bilayer and multilayer diamond films are coated on cemented tungsten carbide (WC-Co) substrates by adopting a bias-enhanced hot filament chemical vapor deposition (HFCVD) technique. Tribological properties of the diamond films are evaluated by using a reciprocal tribometer without lubrication. Further milling tests are carried out to examine the cutting performances with sintered zirconia ceramics as workpiece comparatively. In friction test against zirconia ceramics, the monolayer NCD film shows the lowest friction coefficient (0.128) because of its smooth surface. Also, the bilayer diamond film with surface coating of NCD layer (MNCD) and both of the multilayer diamond films exhibit good friction property while the monolayer MCD film has the largest friction coefficient (0.292). The milling test demonstrates that the monolayer diamond (MCD and NCD) coated milling tools show poor tool life due to abrasive action of hard workpiece. Working life of all the bilayer and multilayer diamond coated tools is enhanced, but large area shedding of coatings appears after some milling passes except the multilayer diamond film with surface coating of NCD layer (MNMN-CD). The multilayer film (MNMN-CD) presents superior machining performance and its working life increases by 3–7.5 times compared with the monolayer diamond coated ones.

THE EFFECTS OF BORON DOPING ON RESIDUAL STRESS OF HFCVD DIAMOND FILM FOR MEMS APPLICATIONS

In this study, the residual stress of boron-doped diamond (BDD) films is investigated as a function of boron doping level using X-ray diffraction (XRD) analysis. Boron doping level is controlled from 1000[Formula: see text]ppm to 9000[Formula: see text]ppm by dissolving trimethyl borate into acetone. BDD films are deposited on silicon wafers using a bias-enhanced hot filament chemical vapor deposition (BE-HFCVD) system. Residual stress calculated by [Formula: see text] method varies linearly from [Formula: see text]2.4[Formula: see text]GPa to [Formula: see text]1.1[Formula: see text]GPa with increasing boron doping level. On the BDD film of [Formula: see text]1.75[Formula: see text]GPa, free standing BDD cantilevers are fabricated by photolithography and ICP-RIE processes, then tested by laser Doppler vibrometer (LDV). A cantilever with resonant frequency of 183[Formula: see text]KHz and [Formula: see text] factor of 261 in the air is fabricated.

Tribological Properties of MCD Films Synthesized Using Different Carbon Sources When Sliding Against Stainless Steel

The carbon source adopted in deposition processes of bias-enhanced hot filament chemical vapor deposition diamond films has significant influences on basic, mechanical and tribological properties of as-deposited films. In the present study, pristine microcrystalline diamond (MCD) films are deposited on both WC-6 wt% Co flat and drawing die substrates, using the same deposition parameters and four typical carbon sources, including the methane, acetone, methanol and the ethanol. As-obtained MCD-coated and WC–Co flat specimens are all applied for standard tribotests, systematically analyzing the typical stages of their friction coefficient curves as functions of the sliding time, differences between tribological properties of MCD films deposited using different carbon sources, as well as effects of the normal load and the sliding velocity adopted in the test, which are closely related to their surface features, composition transformations and mechanical properties. Moreover, MCD-coated and WC–Co drawing die specimens are applied for special-designed wear tests in order to compare their wear rates and removal times, further clarifying the material removal mechanisms, as well as similarities and differences compared with actual applications of diamond-coated drawing dies.

The deposition parameters in the synthesis of CVD microcrystalline diamond powders optimized by the orthogonal experiment

In the present work, microcrystalline diamond powders are deposited by using a bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. Mirror-polished silicon wafers are served as substrates, pretreated by the scratching process for 10–15s. A systematic investigation is under taken into the combined effects of deposition parameters on nucleation and growth characteristics of microcrystalline diamonds, based on the orthogonal collocation method. The results show that the morphology of final microcrystals depend mainly on that of nuclei rather than the deposition parameters, while the quality and grain size of crystals largely depend upon the deposition parameters. A high reactor pressure (3–4.5kPa) in the nucleation process is a necessary condition for depositing the ideal nuclei with the single-crystal structure and euhedral diamond faces. Then under a set of optimized growth parameters, the final single crystals exhibit the regular-shaped morphology and smooth surfaces. The CVD microcrystals with various grain sizes in the range of 0.3–2μm can be obtained by regulating the deposition time; moreover, they have a dramatically narrow particle size distribution, meeting the requirements on certain types of commercial powders without the process of sieving grain.

Comparisons of HFCVD diamond nucleation and growth using different carbon sources

The differences between the nucleation, growth and basic characteristics of bias-enhanced hot filament chemical vapor deposition (BE-HFCVD) microcrystalline diamond (MCD) films fabricated under the different carbon source (methane, acetone, methanol and ethanol) environments are studied in this article, adopting SiC chips as substrates. With the same commonly-used nucleation parameters, acetone and ethanol can provide either higher nucleation density (ND) or larger nuclei size (NS). Besides, under the same commonly-used growth conditions, relatively higher growth rate (R) of the MCD film is obtained adopting methanol than methane, and both acetone and ethanol can further increase it. Moreover, as characterized by the X-ray Diffraction (XRD) and Raman spectroscopy, the MCD film fabricated using methane shows much lower total residual stress (σ), better film quality and lower (220)/(111) ratio compared with those fabricated using all the other carbon sources. The above results can be attributed to the presence of oxygen elements, the different dissociation energies of chemical bonds in the carbon sources, the different quantities of CH3 radicals generated from the carbon sources or the different amounts of defects in as-deposited diamond films. Based on the present study, it is suggested that the carbon source should be reasonably chosen in order to, respectively, improve the film quality or obtain high ND, NS and R.

Effects of working pressure and substrate temperature on the structure and mechanical properties of nanocrystalline SiC thin films deposited by bias-enhanced hot filament chemical vapor deposition

The effects of working pressure and substrate temperature on the structure and mechanical properties of nanocrystalline SiC films deposited by bias-enhanced, hot-filament chemical vapor deposition using tetramethylsilane/H2 gas mixtures were investigated. Experiments were performed at over a working pressure range of 0.5kPa to 1.5kPa, and the substrate temperature was varied from 520°C to 720°C. Field emission scanning electron microscopy, X-ray diffraction (XRD), Raman scattering analyses, and nanoindentation experiments were performed to characterize the morphology, phases, and mechanical properties of the deposited films. These experimental results indicate that the working pressure and substrate temperature had a great influence on the morphology, phases, and mechanical properties of the deposited films. XRD analyses of all thin films fabricated revealed (111) and (220) peaks, but peaks associated with the (200), (311), and (222) planes gradually disappeared with increasing gas pressure. Raman spectroscopy demonstrated the presence of the Raman peaks corresponding to the TO and LO phonon modes of SiC, as well as the D and G peaks of graphite. By adjusting the working pressure and substrate temperature, the nanocrystalline SiC film with the higher hardness and elasticity modulus of approximately 23GPa and 320GPa, respectively, was obtained at a working pressure of 0.75kPa and substrate temperature of 620°C.

Tribological Properties of CVD Diamond Films against Zirconia Ceramic

Microcrystalline diamond (MCD), nanocrystalline diamond (NCD) and microcrystalline and nanocrystalline composite diamond (MNCD) films are all deposited on flat square shaped WC-6%Co substrates by using bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. The diamond films are characterized with scanning electron microscope (SEM) and Raman spectrum. Typical diamond film features are exhibited in the observation of SEM and the analysis results of Raman spectrum. The tribological properties of diamond films against zirconia ceramic are conducted on a ball-on-plate type rotating reciprocating tribometer in ambient air. The average friction coefficients of MCD, NCD and MNCD film in stable period are 0.205, 0.181 and 0.138 respectively. The images of surface topography based on white-light interferometer suggest a very low wear rate of CVD diamond film.

Tribological properties and cutting performance of boron and silicon doped diamond films on Co-cemented tungsten carbide inserts

Boron and silicon doped diamond films are deposited on the cobalt cemented tungsten carbide (WC-Co) substrate by using a bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. Acetone, hydrogen gas, trimethyl borate (C3H9BO3) and tetraethoxysilane (C8H20O4Si) are used as source materials. The tribological properties of boron-doped (B-doped), silicon-doped (Si-doped) diamond films are examined by using a ball-on-plate type rotating tribometer with silicon nitride ceramic as the counterpart in ambient air. To evaluate the cutting performance, comparative cutting tests are conducted using as-received WC-Co, undoped and doped diamond coated inserts, with high silicon aluminum alloy materials as the workpiece. Friction tests suggest that the Si-doped diamond films present the lowest friction coefficient and wear rate among all tested diamond films because of its diamond grain refinement effect. The B-doped diamond films exhibit a larger grain size and a rougher surface but a lower friction coefficient than that of undoped ones. The average friction coefficient of Si-doped, B-doped and undoped diamond films in stable regime is 0.143, 0.193 and 0.233, respectively. The cutting results demonstrate that boron doping can improve the wear resistance of diamond films and the adhesive strength of diamond films to the substrates. Si-doped diamond coated inserts show relatively poor cutting performance than undoped ones due to its thinner film thickness. B-doped and Si-doped diamond films may have tremendous potential for mechanical application.

Tailoring carbon nanotips in the plasma-assisted chemical vapor deposition: Effect of the process parameters

Carbon nanotips have been synthesized from a thin carbon film deposited on silicon by bias-enhanced hot filament chemical vapor deposition under different process parameters. The results of scanning electron microscopy indicate that high-quality carbon nanotips can only be obtained under conditions when the ion flux is effectively drawn from the plasma sustained in a CH4+NH3+H2 gas mixture. It is shown that the morphology of the carbon nanotips can be controlled by varying the process parameters such as the applied bias, gas pressure, and the NH3/H2 mass flow ratios. The nanotip formation process is examined through a model that accounts for surface diffusion, in addition to sputtering and deposition processes included in the existing models. This model makes it possible to explain the major difference in the morphologies of the carbon nanotips formed without and with the aid of the plasma as well as to interpret the changes of their aspect ratio caused by the variation in the ion/gas fluxes. Viable ways to optimize the plasma-based process parameters to synthesize high-quality carbon nanotips are suggested. The results are relevant to the development of advanced plasma-/ion-assisted methods of nanoscale synthesis and processing.

Fabrication of diamond tubes in bias-enhanced hot-filament chemical vapor deposition system

Deposition of diamond thin films on tungsten wire substrate with the gas mixture of ace- tone and hydrogen by using bias-enhanced hot filament chemical vapor deposition(CVD)with the tantalum wires being optimized arranged is investigated.The self-supported diamond tubes are ob- tained by etching away the tungsten substrates.The quality of the diamond film before and after the removal of substrates is observed by scanning electron microscope(SEM)and Raman spectrum.The results show that the cylindrical diamond tubes with good quality and uniform thickness are obtained on tungsten wires by using bias enhanced hot filament CVD.The compressive stress in diamond film formed during the deposition is released after the substrate etches away by mixture of H_2O_2 and NH_4 OH.There is no residual stress in diamond tube after substrate removal.

Study on Comparative Experiments of Performance of Conventional and Nanocrystalline Diamond Film

Nanocrystalline diamond film with smooth surface and uniform grains was deposited successfully on Co-cemented carbide using the bias-enhanced hot filament chemical vapor deposition (HFCVD). The surface morphology and chemical quality of film were estimated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. Comparative experiments of tribological and wear performances of conventional and nanocrystalline diamond films were carried out by pin-on-disc tester. The research results show that nanocrystalline diamond film with good tribological performance and high quality can be deposited by regulating the deposition parameters on Co-cemented carbide. The film not only has high adhesive strength but also has smooth surface, low surface roughness, low friction coefficient. The work done in this paper provide the wide application of diamond on complex shape tools, drawing dies and other wear resistant device with experimental reference.

STUDY ON FORMATION OF CARBON NANOTIPS BY NEGATIVE BIAS-ENHANCED HOT FILAMENT CHEMICAL VAPOR DEPOSITION WITHOUT CATALYST

Carbon nanotips were grown on a silicon substrate by negative bias-enhanced hot filament chemical vapor deposition without catalyst, using a mixture of methane, ammonia and hydrogen as the reaction gases. It was evidenced that the plasma caused by the bias played a key role in the formation of the carbon nanotips. Due to occurrence of plasma during growing carbon nanotips, the gases were ionized into various ions. Based on different effects of the ions, a growth mechanism of the carbon nanotips was put forward.

Study on glow discharge effects on catalyst films for growing aligned carbon nanofibers in negative bias-enhanced hot filament chemical vapor deposition system

Aligned carbon nanofibers (ACNFs) were grown on silicon substrates coated with NiFe catalyst films by negative bias-enhanced hot filament chemical vapor deposition (CVD). The growth and structure of the aligned carbon nanofibers were investigated by scanning electron microscopy (SEM). The results indicate that the aligned carbon nanofibers could be synthesized after the glow discharge appears when the negative bias is higher than a certain value, while they are bent if the glow discharge does not appear. Furthermore, the diameters of the aligned carbon nanofibers are reduced and their lengths are increased with increasing the negative bias. It is shown that the glow discharge resulting from the negative bias plays an important role in the growth of aligned carbon nanofibers. Here, the effects of the glow discharge on the growth and structure of the aligned carbon nanofibers are discussed.

Improvement of adhesive strength and surface roughness of diamond films on Co-cemented tungsten carbide tools

Diamond-coated tools were fabricated using Co-cemented carbide inserts as substrates by the bias-enhanced hot filament chemical vapor deposition. The surface of the WC–Co substrate was decarburized by microwave plasma with Ar–H 2 gas. Effect of the new substrate pretreatment on the adhesion of diamond films was investigated. A boron-doped solution was brushed on the tool surface to diffuse boron into the substrates during diamond deposition. A new process was used to lower the surface roughness of diamond thin films by appropriately controlling acetone concentration and reactive gases pressure. It consists of a two-step chemical vapor deposition procedure that includes, first, the deposition of the rough polycrystalline diamond and then the fine-grained diamond. The research results show that the pretreatment using Ar–H 2 etching decarburization by microwave plasma is an effective method to enhance adhesive strength. An adequate amount of boron dopant solution can effectively suppress the cobalt diffusion to the surface and avoid the catalytic effect of Co at the high temperature. Smooth diamond films with low roughness can be deposited by the two-step CVD process. It is of great significance for improvement of the cutting performance of diamond-coated tools using the above new technology to deposit diamond coatings with the low surface roughness and high adhesive strength on WC–Co substrates.