Papers by Author: Zhen Fan

Abstract: In this paper, both the TiB₂/SiC bilayer films and the carbon-doped TiB₂ (TiB₂-C)/SiC bilayer films (SiC films as interlayer) were successfully deposited on quenched Cr12MoV steel substrate through magnetron sputtering technology, and the carbon-doping effect on microstructure and friction/wear properties of TiB₂ films were investigated. The results show that the doped-carbon presented in manner of sp³C-C and sp²C-C bonds i.e. DLC (diamond-like carbon). As sliding against steel balls under dry frictional condition, the doped-carbon strongly decreased the friction coefficient of the films and the material transfer from the friction pairs to the films. At the same time, the doped-carbon reduced the wear rate of the films, the wear rate of the TiB₂ films and the TiB₂-C films were both in the magnitude order of 10^{−5 mm3} m⁻¹ N⁻¹, this is due to more material transfer significantly adhered on TiB₂ films than on TiB₂-C films.

Abstract: A wear-resistant SiC (silicon carbon) film on titanium substrate was prepared by magnetron sputtering technology. The film exhibits low nano-hardness of 12.1 GPa and low Young's modulus of 166.2 GPa together with superior friction/wear properties. As sliding against Si₃N₄ (silicon nitride) ball (2 mm in radius) at room temperature under Kokubo simulation body fluid condition, the film exhibited the friction coefficient of about 0.215 and the special wear rate in the order of magnitude of 10⁻⁵ mm³/ Nm even at the load of 500g without film cracking and interface delaminating. The high film-cracking and interface-delaminating resistance is due to the low hardness of the film and the good film/substrate modulus match caused by the low elastic modulus of the film.

Abstract: Equal channel angular pressing (ECAP) of 3003Al ingot has been performed at room temperature, with an imposed equivalent strain of ~0.5 for single pass, and the refinement/distribution of inclusions and the hardness/dislocation of the alloy were examined. The results show that the first pass ECAP processing refined the inclusions (AlFe (Mn)Si) of the alloy considerably, with the size variation from 5-15μm length/1-2μm width to 1-3μm length/1-2μm width. In addition to the refinement, the first pass ECAP processing improved significantly the distribution of the AlFe(Mn)Si inclusions, and introduced high density of dislocations, leading to ~66.7 % increase of hardness. It was found that with the increase of number of ECAP processing passes, the distribution of AlFe(Mn)Si inclusions were increasingly more uniform, while the size of inclusions, the hardness and dislocation density (dislocation strengthening) of the alloy kept almost unchanged. The present results demonstrate the possibility of ECAP as an effective tool to refine AlFe(Mn)Si inclusions of aluminum alloys.

Abstract: Hydrogenated nanocrystalline silicon (nc-Si:H) films were deposited on glass substrates using Radio frequency plasma-enhanced chemical vapor deposition(RF-PECVD)from a B2H6/SiH4/H2 gas mixtures. In this paper, we mainly changed the Borane-Silane flow rate ratio (β), while other parameters were kept constant. Raman spectrum and X-ray diffraction were employed to investigate the micro-structure of the films, and the indentations were used to measure the mechanical characters (the Young’s modulus (E) and hardness (H)). The Raman spectrum showed that, withβincreasing the crystalline fraction decreased, which indicated that more boron doped might not be propitious to the formation of crystalline of the thin films. XRD spectrum revealed that the films have a remarkably preferential orientation. The analysis of the Young’s modulus and hardness by TriboIndenter nano system suggested that the increase inβhad concernful effects in the decrease of E and H values, so we can control the mechanical characters of the thin films by means of changing the doped concentrations. In view of these results, it may be concluded that the use of lowβconditions might lead to growth of nc-Si:H films with high crystallinity, and as well high Young’s modulus and hardness.

Abstract: A DLC/SEBS/A187/Si multilayer was prepared by self-assembled monolayer (SAM) method and pulse filtered catholic vacuum arc source (FCVA) technology. Microstructure and frictional properties of the film were investigated by using X-ray photoelectron spectroscopy (XPS), AFM, SEM and UMT-2MT tribometer. Results showed that the peaks appearing at 287.8eV for XPS demonstrated the successfully graft of SEBS on the couple agent(A187); The surface of the top DLC film was compactly and uniformly distributed; Friction coefficient of the prepared film was not sensitive to velocity under low load and the coefficient ranged from 0.1 to 0.15, but at high load, the tribological property of the film deteriorated with the increasing of sliding velocity, when the normal load was 2N and the sliding speed was 30 r/min, only the top DLC film was scratched out, but when the sliding velocity increased to 240 r/min, the whole prepared film was scratched out.

Abstract: In order to analyze the effect of proceeding on the mechanical and tribological properties of DLC films. Three DLC films samples on single silicon wafers were prepared by CVD method. The changed bias voltages were 300V, 350V, 450V separately. The structure and topography of prepared films were studied by Raman spectroscopy and atomic force microscopy (AFM), respectively. The hardness and elastic modulus together with friction coefficient of DLC films were measured by Tribolab system. According to the Raman spectra, the G and D peak shift to left with the increasing of bias voltage. Nano indent showed that the hardness (H) of the DLC films decreases from 19.63GPa to 18.12GPa with the increasing of bias voltages, and the value of elastic modulus (E) is also behaving the same trend as H from 157.95GPa to 146.95GPa. Friction coefficients of the three samples were measured by nano-scratch method under the constant normal load of 1000uN and the slide velocity of 3 um/sec, the corresponding friction coefficient is 0.0804 for DLC300, 0.0508for DLC350 and 0.0594 for DLC450 separately, which indicates that high hardness materials may not necessarily the perfect frictional material, but compound properties of hardness and elastic modulus

Abstract: Thin DLC film is in need for higher magnetic storage density. Surface modification and materials removal of DLC films were carried out in order to estimate the reliability of the ultra thin DLC films. Atomic force microscope (AFM) was used to investigate the wear resistance, surface modification and mechanical reliability of the films. Wear test by contact AFM indicated that wear depth under the same load was varied at different thick films. The local modification is studied using conductive atomic force microscope (C-AFM). Especially, topography change is observed when DC bias voltage applied. Experimental results show that the DLC surface is not modified after direct current applied on the tip. While positive voltage is applied on the DLC film surface, the nanoscale pit on the surface is formed clearly. According to the interaction force between CoCr coating MESP tip and the DLC film surface, as well as the Sondheimer oscillation theory, the “scale wing effect” of the pit is explained. Electromechanical coupling on the DLC film indicates that the depth of pit increases with the augment of force applied on surface when normal force is less than a certain threshold pressure.

Abstract: Micro-flowing technique gained popular applications in microdevices of microelectromechanical systems (MEMS), and the performance of micro-devices is greatly determined by the properties of micro-flow. This paper studied the characteristics of different viscosity fluid flowing over microchannels with different diameters and lengths under low pressure driving, and the influence of scale effects on the flowing characteristics of low viscosity fluids was also examined. The experiments studied the flow rate–pressure characteristics of distilled water flowing over microchannels with diameter of 13 μm, 20 μm, and silicon oil flowing over microchannels with diameters of 50 μm, 100 μm. The results indicate that, when the diameter of micro-channel is more than 20 μm, the flowing characteristics of distilled water and silicon oil agrees well with conventional flow theory, and when the diameter of microchannels is 13μm, the flowing characteristics are related to the length of micro-channel. When the length is relatively shorter, the flowing characteristics are almost in agreement with the conventional flow theory. When the length reaches 100 mm, the flow rate is much higher than the values predicted by theoretical calculation when the length reaches 100 mm. It is obvious that scale effect arises when the length arrives to 100 mm and the velocity slippage results in the great increase of flow rate.