Wen Zhuang Lu

Study on EDM Polishing of CVD Diamond Films

Chemical vapor deposition (CVD) diamond is known for its superior characteristics such as hardness, toughness and wear resistance. However, due to these factors, machining CVD diamond is a difficult material removal process. A new technique to polish CVD diamond film efficiently is reported in the present paper. In the CVD deposition process, boron was doped into diamond to fabricate high-quality semi-conductive film, which make it possible to machine diamond film by electro discharged machining (EDM) method. The relationship between EDM parameter and removal processing was investigated in details. The machined surface of boron doped (B-doped) diamond films was studied by Scanning Electron Microscope (SEM) and Raman Scattering Spectroscopy (Raman). The experimental results show that EDM polishing is a highspeed material removal and low cost method for CVD diamond polishing. When the discharge current and pulse-on time increase in a certain range, the cutting-off speed and roughness will increase correspondingly. The roughness of EDM polished CVD diamond film surface is Ra<0.5μm when the discharge current is at 4A and pulse-on time is at 200μs.

Study on Mechanical Polishing for CVD Diamond Films of Forming Nucleus Surface and Growing Surface

In the present work, high power DC arc plasma jet chemical vapor deposition (CVD) is used to prepare diamond films with full width half magnitude (FWHM) less than 10 wave numbers at 1332 cm−1 Raman peak. During the polishing process, diamond film is hold against the stainless steel holder, which rotates and swings when the sample comes into contact with the cast-iron plate. Average surface roughness of the forming nucleus polished surface and growing polished surface is 560nm, 90nm respectively. And the materials removal rate is quite different. Fine crystal grain of the forming nucleus surface and the thick column crystal of growing surface are dominant in structure. In the meantime, effects of the size of the abrasive power, the applied force and polishing direction are also discussed. A profilometer, an Raman spectroscopy, X-ray diffraction and a scanning electron microscope have been used to evaluate the surface states of diamond films before and after polishing. This result reveals an. improvement of polishing efficiency and a great potential for commercial application.

Preparation of Nanocrystalline Diamond Films on Molybdenum Substrate by Double Bias Method

The synthesis of nanocrystalline diamond film on polycrystalline molybdenum substrates was carried out by using of self-made hot filament chemical vapor deposited (HFCVD) system. Positive bias voltage on the grid electrode on top of hot filaments and negative bias voltage on the substrate were applied. High purity and extremely smooth nanocrystalline diamond films were successfully prepared by using the double bias method. Raman, SEM, XRD and AFM results show that the diamond films obtained have grain sizes less than 20nm, nucleation density higher than 1011cm-1. The mechanism of double bias is also discussed in this paper. The positive grid bias increases the active, decomposition and ionization of hydrogen and methane molecules, while negative substrate bias helps positive carbon-containing ions bombard the substrate that leads to the high nucleation density of the diamond film.

Analysis of Interlayer between WC–Co and CVD Diamond Film

Electroplated Cr, Ni and Cu were used as interlayer for chemical vapor deposition (CVD) diamond coating on WC–Co cemented carbide cutting tools. The electroplated interlayers were studied by Scanning Electron Microscope (SEM), Electron Probe Micro Analyzer (EPMA) and X-ray diffraction (XRD). The CVD diamond coatings were studied by SEM and Raman Scattering Spectroscopy (Raman). The experimental results show that there is diffusion bonded interface between electroplated layer and WC-Co substrate after H plasma treatment, the bond between electroplated layers and WC-Co substrate changes from mechanical bond to metallurgical bond and the adhesion becomes stronger. Electroplated Cr interlayer forms new phases of Cr3C2 and Cr7C3 under CVD conditions, while electroplated Ni and Cu interlayers do not form carbides under CVD conditions. Cr carbides have good chemical compatibility to diamond, and they are propitious to diamond nucleation and growth during the deposition period. The diamond crystal microstructure, diamond quality and adhesion on Cr interlayer are better than those on electroplated Ni and Cu interlayers.

Computer Simulation on the Motion Tracks of Ice Fixed Abrasives Polishing

Ice fixed abrasives (IFA) polishing is a novel ultra-precision machining method. The motion tracks of abrasives during IFA polishing have an important effect on the quality of the machined silicon wafer. Firstly, the motion tracks of IFA polishing are theoretically analyzed in this paper. It is founded that the paths of any point in the IFA polishing pad relative to the wokpiece are a group of cycloids. Then, the motion tracks of single abrasive and multiple abrasives in the IFA polishing pad are simulated respectively. The results show that increasing the eccentricity is beneficial to the enlargement of the size range of polishing process. With the increasing of the speed ratio between the IFA polishing pad and the workpiece, the abrasive at higher speed can leave longer tracks on the workpiece than that at lower speed at the same time. The more the abrasives, the more uniform the mark density under the influence of more abrasives.

Contact Stress Analysis of NCD Coating on Roll Ball of Ball Bearing

Chemical vapor deposition nanocrystalline diamond (NCD) film has numerous unsurpassed properties, among them, bulk modulus, hardness; abrasion resistance and thermal conductivity are notable ones like polycrystalline CVD diamond film. The super mechanical properties have made NCD film to be an effective way to improve the resistance performance of the ceramic bearing and extended its life. The contact stress of bearing ball with NCD coating in elastic contact was analyzed. Factors such as substrate material, thickness of NCD coating, load and interlayer material which affect the shear stress distribution of NCD coating on bearing ball were investigated. The results show that substrate with low elastic modulus and heavy load will enlarge the difference of equivalent stress value at NCD/substrate interface. Thick film will make the stress distribution at the interface uniform. Soft interlayer should be inhibited to avoid extra stress in contact status.

Investigation on Strain Films in the Thin Film Resistance Strain Gauge

Strain films in the thin film resistance strain gauge are prepared by magnetron sputtering method. Some results concerning the electromechanical and structural properties of nichrome (Ni80Cr20 wt.%) thin films are presented. As compared to the well-known Ni-Cu (constantan) alloy film, which are widely used for manufacturing pressure and force sensors, nichrome (Ni80Cr20 wt.%) thin films exhibit gauge factor values of the same order of magnitude, but they are much more corrosion resistant and adherent to the substrate. The influences of composition and post-deposition annealing on the electrical resistance, temperature coefficient of resistance (TCR) and gauge factor of nichrome (Ni80Cr20 wt.%) thin films are discussed.

Study of the Thermal and Intrinsic Stress of Large Area Diamond Film Prepared by HFCVD

High residual stress that includes thermal and intrinsic stress is an obstacle to the further application of chemical vapor deposited diamond thick film. In this paper, CVD diamond thick film was deposited on silicon substrate by hot filament chemical vapor deposited (HFCVD) system. The finite element analysis (FEA) simulation and experimental research were carried out on the thermal and intrinsic stress of large area diamond thick film. The FEA model is set up to investigate the distribution and magnitude of thermal stress. The intrinsic stress is studied by X-Ray diffraction “sin2ψ” method. The thermal stress and intrinsic stress are both compression stress. Simulation results show the discontinuous sharp of the diamond film result in the stress concentration and low cooling velocity is a good way to reduce thermal stress. The intrinsic stress is correlative with the microstructure and non-diamond component of diamond film. The origin of the intrinsic stress is discussed in detail in this paper.

Effects of CH4 Concentration on CVD Diamond Coatings Deposited on Cemented Carbide Cutting Cools

Chemical vapor deposition (CVD) diamond coatings were deposited on cemented carbide cutting cools by an electron-assisted hot filament chemical vapor deposition (EACVD) equipment developed by the authors. The CVD diamond coatings were studied by Scanning Electron Microscope (SEM) and Raman Scattering Spectroscopy (Raman). The experimental results show that CH4 concentration in the source gas performs great influence on the micro-structure, surface roughness, composition, residual stress and adhesion of the CVD diamond coatings. The increase of CH4 concentration results the change of diamond crystal from {111} orientation to {100} orientation, the decrease of the surface roughness and the increase of sp2 carbon in the CVD diamond coatings. A residual compressive stress exists in the CVD diamond coatings. The residual stress decreases with increasing CH4 concentration. A higher or lower CH4 concentration tends to reduce adhesion stress of the continuous CVD diamond coatings.

Influence of Substrate Temperature on Microstructure and Properties of Ti-Si-C Film

Ti-Si-C films were prepared on cemented carbide by chemical vapor deposition. The reactive gas system was CH4, (CH3)4Si, TiCl4 and H2. The film was analyzed and tested by SEM, AFM, EDS, XPS, microhardness tester, friction and wear tester. The results indicate that the film is continuous and dense. At higher substrate temperature, the hardness of the film will be higher. When the substrate temperature is 850°C, the adhesion of the film is highest with coefficient of friction only 0.14.