Advanced Materials Research Vols. 97-101

Abstract: A new type in situ reinforcing phase TiC+Cr7C3 ceramal composite coating was fabricated on substrate of Q235 steel by plasma transferred arc (PTA) weld-surfacing process using the mixture of ferrotitanium, ferrochromium, ferroboron and ferrosilicium powders. Microstructure and wear performance of the coating were investigated by means of X-ray diffraction (XRD), scanning electron micrograph (SEM), energy dispersive X-ray analysis (EDS), microhardness tester and wear tester. Results show that the composite coating consists of TiC, primary phase Cr7C3 , (Cr,Fe)7C3 and austenite. The composite coating is metallurgically bonded to the Q235 steel substrate. TiC particles present cubic and “dendrite flower-like” shape in the composite coating. The coating has high microhardness and excellent wear resistance under dry-sliding wear test conditions.

Abstract: Four kinds of coating materials and two kinds of brush plating materials were screened and sprayed on the surface of valve ball by plasma spraying technology and brush plated on the surface of valve seat by electrical brush technology, respectively. The wear resistance of the sealing pairs and the properties of the plasma sprayed coatings were tested. The results indicate that the sealing pair composed of the valve ball with the plasma sprayed coating of Al2O3-TiO2 and the valve seat with the brush plating layer of nickel tungsten has best combination property. The gap of the sealing pair at room temperature and the leakage rate at elevated temperature of the high temperature ball valve were obtained by FEM method and analysis method, respectively. Therefore, the open and close torque of the high temperature ball valve was determined. According to the results of the research, the failed ball valve was remanufactured, and the performance inspection was also conducted. The remanufactured ball valve has much longer service life than the original one and its sealing behavior was also improved significantly.

Abstract: Pb/WC-ZrO2, Pb/Ag-WC-ZrO2, Pb/WC-ZrO2-CeO2 composite inert electrodes were prepared on aluminum alloy substrate by electrodeposition method from fluorboric bath containing suspension of WC, ZrO2, CeO2 and Ag particles. The stable state polarization curves of oxygen evolution and liner regression curves were obtained. Compared with Pb-1%Ag alloy, the oxygen evolution overpotential of Pb/10.02%WC-3.58%ZrO2, Pb/0.84%Ag-10.01%WC-3.64%ZrO2 and Pb/5.84%WC-2.29%ZrO2-1.32%CeO2 inert electrodes is lower in the range of 12-27mV, the exchange current density is higher two magnitudes above, showing that their catalytic activity of oxygen evolution is better.

Abstract: Square-wave pulse current was used to electrodeposit Ni-W-P-CeO2-SiO2 composite coatings. The influence of pulse on-times, off-times and peak current densities on properties of the composite coatings was researched. The microhardness, chemical compositions and microstructures were evaluated by EDX, SEM and microhardness tester. The results show that the composite coatings possessed higher microhardness and fine-grained structure. The crystal sizes of the composite coatings were found initially to decrease with the rise of pulse on-times before it started to increase with further increasing pulse on-times. Decreasing pulse off-times or increasing pulse peak current densities resulted in considerable refinement of crystal sizes.

Abstract: With the miniature of micro-electromechanical systems (MEMS), surface effect is substantially increased, and the resulting friction, abrasion and stiction are becoming bottlenecks of the development of MEMS industry. In this paper, firstly, the feature size and topography on lotus leaf surfaces is investigated, as well as the mechanism of lotus effect applied in MEMS to reduce friction and prevent stiction is analyzed; secondly, two approaches of fabricating bionic silicon surfaces with lotus effect are proposed; finally, test results on the micro tribological performance of the mimicked silicon surfaces are presented, which demonstrates that to mimic lotus effect on silicon surfaces is a novel approach to prevent stiction and reduce friction . However, the effectiveness of stiction prevention and friction reduction is related to the size and shape of the textured structures.

Abstract: In this paper, aluminum films were deposited on the TiAl alloy by multi-arc ion plating (MAIP) and subsequently diffusion-treated under 720°C for 4h. It is revealed by XRD and SEM/EDS that the film consisted of Al turn to an outer Al2O3 layer and inner TiAl3 layer after diffusion treatment. Cyclic oxidation tests show that the surface of the film formed a compact and continuous Al2O3 layer that prevents the TiAl substrate from oxidation, and the oxidation rate of the specimen with Al diffusion film is as low as 1.84 mg/cm2. The MAIP Al film after diffusion treatment is effective in improving the high-temperature oxidation resistance of TiAl alloys.

Abstract: According to the actual experimental condition and theoretical analysis, a finite element model was established to describe the surface modification process of scanning electron beam of 6A02 aluminum alloy. The phase change process and thermal radiation were considered in the simulation. The temperature simulation revealed the ultrahigh rate of the heating and cooling, rapid melting and re-solidification within seconds in the range of millimeters in depth. The calculated melting zone was an irregular semicircle, the x-axis length was about 2.9mm, and the axial depth was about 1.4mm. This research will predict the melting condition.

Abstract: The NiCoFeCrAl3 high entropy alloy coating with a little addition of C, Si, Mn, Mo has been succesively synthesized by laser cladding. The results show that simple solution phases of ordered BCC and a small fraction of FCC are obtained with fine equaixed dendrites morphology. Because the fine grain strengthening obtained by rapid solidification and the additived small atomic elements like C, Si further increase the distortion of the solid solution lattice, The microhardness of the coating reached above 800 HV and is 50 % higher than previous study on the similar composition by arc melting technique.

Abstract: Silver films were prepared on the glass substrate by electron-beam vapor deposition. The reflectivity of the Ag thin film was measured by a Perkin-Elmer Lambda spectrophotometer in the wavelength region of 450-680 nm. The experimental measurements of reflectivity were validated with the numerical results using the Essential Macleod software. The surface topology and microstructure of the film were examined by means of atomic force microscope (AFM). The effects of the thermal and humidity on the reflectivity of the Ag film were examined by the environmental test. Nanoindentation tests were employed to determine the hardness of the film. The measured hardness of the Ag thin film was found to depend on the penetration depth.

Abstract: In order to explore electrodeposition mechanism of composite plating, the effect of SiO2 particle concentration in the electrolyte on the component of Zn-SiO2 coatings was studied, and the control steps of composite electrodeposition were analysed. The results show that two-step adsorption of particles on the cathode proposed by Guglielmi also occurs during Zn-SiO2 composite electrodepositing process. When SiO2 particle concentration added in sulfate electrolyte is more than 10 g/L, the control-step of the electrodepositing process will turn from loose adsorption to strong adsorption, while the turning point of particle concentration in chloride plating system is 4 g/L. Through comparing and analysing the relationship between , and c, it is testified that Guglielmi model only can be effective when composite electrodepositing process is controlled by strong adsorption, while due to hydromechanical effect, it is not available when loose adsorption is dominant, and the critical concentration is not fixed in different plating system.