Duo Sheng Li

Effect of DC-Plasma Arc Behavior on Growth of Diamond Film

DC-Plasma arc behavior is one of the key factors on growth of diamond film. The results show that keeping steady DC-Plasma arc can grow better quality diamond film. In a long-time growth of diamond film, there is sediment carbon on about 5mm border-entad anode annulus, which was proved to be graphite. It results in fluctuating and instability of DC-Plasma arc and in the DC-Plasma density, which causes graphite generation and much stress in the film. By means of adjusting anode annulus assembly, pausing the supply of carbon source and increasing H2, the problem of sediment carbon cab be effectively resolved. Finally, the mechanism of the effect of arc behavior on growth of diamond film is discussed.

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.

Mechanism of Brittle-Ductile Transition of Single Silicon Wafer Using Nanoindentation Techniques

Hardness, elastic modulus and scratch resistance of single silicon wafer are measured by nanoindentation and nanoscratching using a nanoindenter. Fracture toughness is measured by indentation using a Vickers indenter. The results show that the hardness and elastic modulus at a peak indentation depth of 100 nm are 12.6 and 166.5 GPa respectively. These values reflect the properties of the silicon wafer, the bulk material. The fracture toughness value of the silicon wafer is 0.74 Mpa·m1/2. The material removal mechanisms are seen to be directly related to the normal force on the tip. The critical load and scratch depth estimated from the scratch depth profile after the scratching and the friction profile are 138.64 mN and 54.63 nm respectively. If the load and scratch depth are under the critical values, the silicon wafer will undergo plastic flow rather than fracture. The critical scratch depth is different from that calculated from the formula of critical-depth-of-cut described by Bifnao et al and some reasons are given.

The Design of Noncircular Gear of Constant Pressure Angle and the Realization of Its Wire-Electrode Cutting

This paper brings forward a new type of the tooth profile of noncircular gear—constant pressure angle involute tooth profile, and realizes its wire-electrode cutting. By the design of CAD and CAM, this paper shortens the design time of the noncircular gear and improved the design accuracy of the noncircular gear. By the research of the constant pressure angle involute tooth profile of noncircular gear, this paper has improved the transmission accuracy of the noncircular gear. By the research of the technology of wire-electrode cutting, this paper has improved the manufacturing accuracy of the noncircular gear.

Effects of Methane Concentration on Growth of Carbon Balls in Anode Nozzle and Arc Stability of DCPJ CVD Plasma Torch

High quality diamond film wafers with different thickness are prepared by high power DC arc plasma jet CVD (DCPJ CVD) method using a CH4/Ar/H2 gas mixture. The effects of methane concentration on the growth of carbon balls in anode nozzle and arc stability are studied with theoretical analysis and experimental investigation. The results indicate that different sizes of carbon balls may rapidly grow in the anode nozzle with methane concentration higher than 2 Vol-%, symmetry and uniformity of the rotating arc are strongly affected with the occurrence of carbon balls, which will result in non-uniform deposition of diamond films over a large substrate area. The methane concentration should be controlled at a low level to keep diamond film wafers growth stable. Characterization by X-ray diffraction, Raman spectroscopy and SEM analysis are also carried out.

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.

Mechanism of Brittle-Ductile Transition of Single Silicon Wafer at Different Temperatures

Formation, propagation and length of crack and hardness of single silicon wafer were investigated at different temperatures by means of Vickers indentation, using lower temperature testing unit with semiconductor refrigerating chip and higher temperature testing unit with closed electric furnace. The results show that the hardness of single silicon wafer decreases with the increase of temperature, while the length of crack increases with the increase of temperature. Ductile-brittle transition of the single silicon wafer can occur at different temperatures with the increase of load. When the load is smaller and temperature is lower, no cracks can be found.

Fabrication and Fracture Analyses of SiC Particulate-Reinforced Al Matrix Composites

The fabrication process and fracture characterization of 35 and 65 vol% SiCp particulate-reinforced Al matrix (SiCp/Al) composites have been investigated. SiCp composites having different volume fractions of the n-SiCp were synthesized via by pressureless-infiltration at near-net-shape route and were uniaxially tested at room temperature. The SiC particles were mixed with silicasol as an inorganic binder in distilled water. The mixtures were consolidated in a mold by pressing and dried in two step process, followed by calcination at 1000 °C. The SiCp/Al composites were fabricated by the infiltration of Al melt into SiC performs. The experimental results show that volume fraction of reinforced particles in SiCp/Al composites had a significant influenec on fracture section surface characterization in tensile tests. Composite with 45 vol% SiCp, fracture was firstly happen in Al matrix, shallow dimples and intergranular fractures were seen in all the fractographs. With increasing of vol% SiCp, fracture was more brittle in appearance in the composites and the fracture surfaces were flat and less plastic deformations.

Study on Microstructure Characterization of SiCp/Al Composites

ZL101 Al alloy reinforced with 55% silicon carbide particulate metal-matrix SiCp/Al composite has been fabricated by pressureless-infiltration. The microstructure characterization of composite has been studied by optical microscope (OM), scanning electron microscope (SEM), X-ray spectroscopy (EDX), respectively. The results show that the SiCp are uniformly distributed in Al alloy matrix, however, there are some casting defects such as shrinkage and gas porosities in the matrix. When Mg was added into the composite, it can improve wettability property of between Al matrixes and strengthen particle SiCp and decrease micro-defects such as gas porosities, the Microstructure of SiCp/Al composite prepared was compact and uniform. The SiCp particles evenly distributed in the matrix and without significant partial segregation phenomenon. It improves the whole performance of the composites.

Research on High-Speed Preparation of Micro-Nanocrystalline Diamond Film

Micro-nanocrystalline diamond (M-NCD) Film may be successfully prepared on Mo substrate with DC arc plasmas jet deposition device. This paper studies the influences of carbon source concentration on the shape of M-NCD Film particles under circumstances of stable electric arc, and characterizes the grain size and quality of samples through SEM, AFM and Raman spectrum. The research result shows that, in the state of stable electric arc, relatively low carbon source concentration (1%) could deposit high-quality microcrystalline diamond film on the substrate, with a growth rate of up to 8.3μm/h and grain size of about 2～4μm; relatively high carbon source concentration (10% or 15%) could deposit high-quality nanocrystalline diamond(NCD) film on the microcrystalline diamond film at high speed, with a growth rate of up to above 12.6μm/h or 19.7μm/h, grain size of about 4～80nm and average grain size of 27.4nm.