Papers by Author: Lu Wang

Abstract: The objective of the present investigation is to study the oxidation resistance of SiO₂/SiC coating on carbon fiber by electrolytic plasma spraying. The SiO₂/SiC coating can be easily prepared within several tens seconds through this approach. The effect of spraying parameters (fixed point 5s and spray 5 times at the speed of 20mm/s) on the microstructure and oxidation resistance properties of coatings was discussed in this paper. Scanning electronmicroscopy (SEM), energy dispersive spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) and DTG have been used to characterize the SiO2/SiC coatings. It was demonstrated that fixed-point spray 5s has better density and oxidation resistance coating, and the oxidation resistance increased by 12% compared with spray 5 times at the speed of 20mm/s. The fixed-point spray 5s coating was mainly composed of SiO₂ and SiC. The SiO₂ relative content was 72.6% and the SiC relative content was 27.4%.

Abstract: A new technology was introduced to prepare anti-oxidant coating on graphite. The whole procedure could be controlled easily when compared with the conventional technology. According to the preliminary experiment, the combining power between the substrate and the coating was good. The coating was uniform and well-distributed. Anti-oxidation test at 1300 oC showed that the coating could prevent substrate from being oxidized. So the new technology had a great advantage while applied in the industrial production and it would lay a solid foundation for the large scale industrialization.

Abstract: A novel aqueous plasma electrolysis applied for depositing a uniform and continuous Al₂O₃/Y₂O₃ ceramic coating on each fiber within a carbon fiber bundle are reported in this study. All equally spaced tungsten wires generated plasma arc, where the plasma was overlapped, excluded and extruded each other, finally a cylindrical plasma arc zone was formed, promoting the full coverage of the coating on each fiber. The Al₂O₃/Y₂O₃ coating protected the carbon fiber from oxidation above 850^oC. Similarly, the coating significantly improved the oxidation resistance of the carbon fiber with the mass loss of ~5% after isothermal oxidation in N₂ atmosphere at 800°C for 30 min, compared to ~14% of bare carbon fiber. By the movement of the T300 carbon fiber bundle, 1500 m coated carbon fiber bundle with the high-quality Al₂O₃/Y₂O₃ coating deposited on each fiber was successfully realized. It is believed that the novel aqueous plasma electrolysis will find a wide range of applications in modifying the interface of the carbon fiber reinforced composites. The present investigation will also open up a new horizon for preparing a protective coating on each fiber within two/three-dimensional carbon fiber fabric.

Abstract: Amorphous Al-Cu-Ti metal foams with the porosity of 65% were prepared by spark plasma sintering with both the diameter and height of 10 mm. The SPS process was carried out under the pressure, the dwell time and the temperatures of 300 MPa, 5min and 623-673K, respectively. The microstructure and mechanical behavior of the amorphous Al-Cu-Ti metal foams were investigated. The results showed that sintering at high temperatures improved the crystallinity and adhesion between particles. The intermetallic compounds, i.e. Al-Ti, Al-Cu and Al-Cu-Ti were identified from the XRD patterns. It was found that weak adhesion and irregular shape of NaCl might reduce the mechanical properties. The highest strength of amorphous Al-based metal foam sintered at 653K, 300MPa was 7.97MPa.

Abstract: _{Subscript text}High-temperature chemical stabilities of Hf₆Ta₂O₁₇/Al₂O₃, Hf₆Ta₂O₁₇/YSZ and Hf₆Ta₂O₁₇/Sm₂Zr₂O₇ were studied for thermal barrier coatings (TBCs). The mixed powders of Hf₆Ta₂O₁₇/Al₂O₃ and Hf₆Ta₂O₁₇/YSZ were annealed at 1600°C for 8 hours in air, and the mixed powders of Hf₆Ta₂O₁₇/Sm₂Zr₂O₇ were annealed at 1200°C for 8 hours in air. The phases of the annealed mixed powders were observed by X-ray diffractometry (XRD). The sample of Hf₆Ta₂O₁₇/Al₂O₃ mixed powder was molded and sintered at 1600°C for 8 hours in air, and the microstructures of the sintered sample were investigated by scanning electron microscopy (SEM). The XRD results revealed that the crystal structure of Hf₆Ta₂O₁₇ had no remarkable changes in the mixed powders of Hf₆Ta₂O₁₇/YSZ and it had changes in the mixed powders of Hf₆Ta₂O₁₇/Al₂O₃. The monocline HfO₂/ZrO₂ phases were found in the mixed powders of Hf₆Ta₂O₁₇/Sm₂Zr₂O₇. The SEM results showed that the boundaries of Hf₆Ta₂O₁₇ and Al₂O₃ crystals were clear. The element composes in crystals were analyzed by energy dispersive spectrometer (EDS), and the EDS results showed that a little amount of Al diffused into Hf₆Ta₂O₁₇ crystals.

Abstract: The deformation micromechanism of Zr50Cu50 bulk metallic glasses under compress loading is studied by means of molecular dynamics. The modified self part of the Van Hove function is used to evaluate the transport properties of clusters in deformation behaviors. It is found that the instable clusters are restricted by the ‘backbone’, a kind of three dimensional network structure formed by close-pack clusters. Local shear transformation zone (STZ) is initially formed in these instable clusters, merge with each other and generate eventually a whole STZ, which penetrates the glasses matrix when the backbone is destroyed with increasing loading.

Abstract: Mobilization production is an effective model to respond to emergency situation, which can organize all kinds of production resources and enlarge production capacity in short time. The design of mobilization production plan needs numerous data and to be revised repeatedly. Therefore, it is very difficult for the traditional design approach to work out right results and forecast the performance of mobilization production plan. A parametric simulation modeling approach is presented in this paper to solve those problems. The approach separates the control logic from modeling elements through creating simulation database, typical model base and control logic base. A model generator is built to automatically create the finial simulation model based on those kinds of bases. The simulation software of AutoMod is applied to realize the modeling process above. Finally, a case study is presented to illustrate the application of the proposed approach.

Abstract: To develop novel and advanced thermal barrier coatings, full-scale numerical simulation of plasma-sprayed functionally gradient materials is conducted in this paper, including the prediction of basic parameters at the nozzle exit, simulation of three dimensional simulation of the plasma jet, modeling of the interaction between the plasma jet and the particles, calculation of flight trajectories and temperature history of flying metal and ceramic particles, the interaction between the molten particles and the substrate, as well as the deposition process of the coatings. Various complex phenomena, such as turbulent effects with chemical reactions in the plasma jet, dispersion status of the particles onto the substrate, and the composition distribution of the functionally gradient materials, are fully taken into account. The numerical simulation results are found to be in good agreement with experimental evidence.

Abstract: A fine-grained magnesium alloy AZ31was obtained through equal channel angular pressing (ECAP).Mechanical properties and the microstructures after deformation under tension and compression were investigated. The tensile strength, compressive strength and the elongation to failure of the fine-grained AZ31 are enhanced due to the reduction of grain size. The compressive ultimate strain (CUS) of the fine-grained AZ31 magnesium alloy is lower than that of the initial state due to the formation of shear bands during compression. The ECAP processed AZ31 magnesium alloy exhibited no tension/compression asymmetry in yielding.