Papers by Author: Feng Xu

Abstract: The performance of CVD diamond coated cemented carbide cutting tool in comparison with K10 uncoated cemented carbide tool in the dry turning of Al-20wt%Si aluminum-silicon hypereutectic alloy was investigated. The obtained results showed a better cutting performance for CVD diamond coated tool in machining Al-20wt%Si, particularly in terms of cutting force, tool wear, surface roughness, when compared with K10. The cutting forces are lower with CVD diamond coated tool and the depth of cut promotes a great increment of the cutting force. The tool wear processes taking place in the tool tips in all cutting conditions. The tool life of CVD diamond coated tool is longer than that of the uncoated K10. The surface roughness Ra increases obviously with the increase of feed rate using a CVD diamond coated cutting tool. A higher feed rate produces surface rougher. The chip morphology in machining of Al-20wt%Si alloy by CVD diamond coated tool is continuous. The tests showed that the CVD diamond coated tool can be applied on the K10 tool at low feed rate to produce high quality surfaces.

Abstract: The contact stress of cemented carbide with NCD coating in elastic contact was analyzed using ANSYS. Factors such as elastic modulus and thickness of NCD film and elastic modulus of interlayer which affect the shear stress distribution of NCD film on cemented carbide substrate were investigated. The results show that the maximum shear stress point moves towards the interface with the increase of film elastic modulus. Film thickness has a significant effect on shear stress distribution of NCD film. High shear stress develops in the film layer with the increase of film thickness. Interlayer with low elastic modulus will cause shear stress concentration in NCD film.

Abstract: Boron-doped micro-nanocrystalline diamond coating may be successfully prepared on Mo substrate with DC arc plasmas jet deposition device. Along with the increase of doped-boron concentration in the film, two-point resistance measurement indicates that film resistance presents exponential decrease; Raman spectrum test shows that, the characteristic peak value of diamond 1332cm-1 in the spectrum moves toward low frequency, the semi-height width of diamond peak, peak D and peak G, etc. in the spectrum is expanded, and the component of non-diamond bonds such as sp2, etc. in the film is increased; SEM and AFM observation shows that, increasing the doped-boron concentration could further subdivide the crystal grains in the film, and is beneficial for the growth of nano- or ultra-nano-crystalline diamond film; film annealing test shows that, micro-nanocrystalline diamond film with higher doped-boron concentration has better thermal stability than the micro-nanocrystalline diamond film without doped boron.

Abstract: The abrasive ice disc chemical mechanical polishing (AID-CMP) is a potential polishing process in the semiconductor industry to realize superior surface finish and planarity for semiconductor wafers. In this paper we investigated the temperature field during GaAs wafer AID-CMP process for a better understanding of AID-CMP. The results show that the AID outer temperature is higher than the inner, and the highest temperature in AID is at the wafer/AID contact zone. The increases of Pc, v, eh and tp will generate more energy and cause more local melting during GaAs wafer AID-CMP process. The AID temperature and the area of highest temperature zone increase with increasing Pc, v, and eh. The nodes temperature increase in every conditions adopted as tp increases. The area of melted zone and thickness of melted ice increase with increasing Pc, v, eh and tp.

Abstract: Chemical vapor deposition (CVD) diamond coatings were deposited on milling cutter substrate using a hollow substrate holder. The substrate is WC–Co cemented carbide contained 6% of cobalt concentration. Structures and stress state of diamond films were analyzed by scanning electron microscopy (SEM) and Raman spectroscopy. It was found that the diamond coating is of the same quality at the same cutting tool deposited on a hollow substrate holder. Diamond (sp3) bonds are better developed with substrate temperature of ~760°C. A higher or lower substrate temperature could lead to a higher non-diamond carbon content in the films. A higher substrate temperature could lead to a higher thermal stress. The compressive stress increases when the substrate temperature is higher or lower than 760°C. The concentration of amorphous phase in the coatings is low with CH4 concentration of 1.0% and 1.5%. A higher non-diamond carbon content and defects in the diamond coatings increase with the increase of CH4 concentration, which leads to the compressive stress value does not increase significantly under a high CH4 concentration.

Abstract: The uniform distribution and the stability of the substrate temperature are the most important factors that deeply affect the quality and the growth rate of diamond films. In this paper, cemented carbide cutters were chosen for substrates, the 3D finite element (FE) model of filaments and substrates was developed in ANSYS 8.0, the calculated results show that the substrate temperature is influenced by the filament temperature, filaments diameter, the quantity of the filaments and the distance between the filaments and the substrates. The 3D finite element model of filaments and substrates also provides a basis for selecting the parameters to obtain uniform diamond films in miniature EACVD system.

Abstract: 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.

Abstract: 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.

Abstract: A stirring mill, an ultrasonic bath and a high-speed shearing emulsifier were adopted to modify the surface characteristics of nanodiamond (ND) respectively. The ζ-potential, size distribution and Fourier transform infrared spectroscopy (FT-IR) of ND were measured to evaluate its properties. Results show that the ζ-potential of ND modified with SHP (either by Mechano-chemical Modification or Ultrasonic measurement) drops sharply. Results also show that the rotating speed of the emulsifier exerts little influence on the size D5 but great influence on the size D95 of ND.

Abstract: Chemical vapor deposited (CVD) diamond film is a good materials for cutting tools as its a series of excellent properties. But because of its polycrystalline morphology, CVD diamond thick film has a rough surface that limits its application in engineering. In this paper, study was carried out on the mechanical lapping of diamond film. It is shown that surface roughness of the film was reduced from Ra 4.5μm to Ra 0.2μm after 50-minute polishing. The surface integrity of polished diamond thick film was investigated, which includes surface roughness, morphology and residual stress. There are a lot of micro defects such as grooves, gas cavities and micro cracks on the polished surface, which are the intrinsic defects generated in the deposition process of CVD diamond film. The tensile stress of the film reduced through polishing as the release of the deformation energy stored in the film.