Papers by Author: Yi Qi Wang

Abstract: Electrophoretic deposition (EPD) technique was applied to deposit carbon nanotubes on a carbon fabric. Optimization of EPD conditions was investigated to improve electrical conductivity for CNTs/carbon fiber hybrid multiscale composites by Taguchi method. Based on design of experiment, a L9(3)4 orthogonal array was chosen to conduct experiments. Due to the electrical conductivity of composites increased with the increasing content of CNTs in composites, it was selected as the response on the analysis of the means (ANOM) and the signal to noise (S/N) ratio. In addition, scanning electron microscopy (SEM) was utilized to examine the distribution of CNTs on the surface of a carbon fabric. The statistical software MINITAB 14 was utilized to determine the optimal deposition conditions.

Abstract: The ceramic coatings were prepared on the T6-tempered Al6061 alloy substrate under a hybrid voltage by PEO treatment in 5-30 min in a phosphate electrolyte. The X-Ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the coating microstructures. With increasing the PEO treating time, the different compositions of coatings eliminate the sharp slope of the microhardness profile. The coatings PEO-treated in 30min presents excellent abrasive resistance property.

Abstract: This research makes comparisons of empirical fatigue-lives between AC8A Al alloy and the metal matrix composites (Al/Al2O3, Al/Al2O3/Al2O3p), and also includes comparisons of fatigue-lives between empirical fatigue-lives and estimated fatigue-lives from regular-periodic load testing, acoustic emission (AE) method to predict fatigue-crack initiation before visible in sight and SEM (Scanning Electron Microscope) photographs of each material. According to the test results of the notched specimen, the fatigue life of the hybrid metal matrix composites and the metal matrix composites, which are more brittle than the base matrix was shorter than that of the base matrix under both types of loads. In addition, the fatigue-life estimated from the damage summation method and that from experiments at random loads were fairly identical.

Abstract: The microstructures and mechanical properties of OFHC copper/STKM 11A for D-tube joints brazed using BAg filler metal at 870 °C for 20 minutes in NH3 atmospheres were performed. Interfacial microstructures were observed in reaction layer. A brazing strength causes of decline with defects of pin hole and base metal by lack of penetration. In tensile test, the properties of joints clearance of 0.01mm are better than other joints clearance that has yield strength of elasticity area with the brazing length of 2.5mm, and also suitable for the case of brazing length of 5.0mm. According to the results of FEA (finite element analysis) on the tensile test, the maximum stress and strain were generated apart from the interface in large deformation. Diffused layer was formed by counter diffusion action of base metal and filler metal layer, and crack between two base metals was not discovered. This is the main reason that fracture of test piece does not appear in copper base metal, and brazing department forms good junctures.

Abstract: High-temperature oxidation resistance of 7 wt.％Y2O3-ZrO2 thermal barrier coatings (TBCs) irradiated by high-intensity pulsed ion beam (HIPIB) has been investigated in a cyclic oxidation condition at 1050 °C ×1 h. The ceramic coating of a tetragonal ZrO2 phase structure was prepared on GH33 superalloy substrates with a NiCoCrAlY bond coat by using electron-beam physical-vapor deposition (EB-PVD). The ceramic coating is composed of columnar grains forming dense clusters spacing with several-μm gaps among grain clusters. The characteristics of the columnar grains disappeared after HIPIB irradiation at the ion current densities of 100-200 A/cm2, and the irradiated surface presented a smoothed, densified feature after the remelting and ablation due to the HIPIB irradiation. The thickness of the densified layer is about 1 μm. After oxidation with 15 cycles at 1050 °C ×1 h, the oxidation kinetics curves of the as-deposited and irradiated TBCs showed a parabolic shape. The weight gain of original sample is about 0.8-0.9 mg/cm2, while the values of the HIPIB-irradiated TBCs decreased to some extent. The lowest weight gain is obtained for the irradiated TBCs at 200 A/cm2 with one shot, being 0.3-0.4 mg/cm2, and those at 100 A/cm2 have a medium weight gain of 0.6-0.7 mg/cm2. The cross-sectional morphologies of HIPIB-irradiated TBCs show less oxidation of the NiCoCrAlY bonding layer, with a thinner thermally grown oxide (TGO) layer. The morphology observation is consistent with the results of cyclic oxidation test. It is found that the inward diffusion of oxygen through TBCs can be significantly impeded by the densified top layer by the HIPIB irradiation, thus limiting the oxidation of the bonding layer, improving the overall oxidation resistance of the irradiated TBCs.

Abstract: The static and dynamic properties on the hoist hook of a vessel are necessary since they are affected by the damages of a static and dynamic load. Al-Si-Mg casting alloy (AC4C-T6) is widely used due to its good mechanical properties as well as the light weight and good casting with complex geometries. This study accomplished a static tension test and an impact test. Based on the test results and fracture surface analysis, we found that there are great differences between the fracture strain and yield stress in the different extracted regions of specimen. In tensile test, yield stress were 205 MPa at a low strain rate of 5 mm/min and 220 MPa at a high strain rate of 25mm/min. In Charpy impact test, impact properties of AC4C aluminum alloy were analyzed by impacting loading versus displacement and impacting energy versus displacement. Compared the fracture strains in different strain rates, maximum fracture strain of low strain rate was mainly 10 % higher than that of high strain rate. There were more than 20 % differences in the strain rate. The ductile and brittle behaviors were showed in low strain rate and high strain rate in static tensile test, respectively. The impact energy reached high when they were extracted from a plane region in the mold. But impact energy reached low when they were extracted from a curved and edge region. It is demonstrated that mechanical properties and impact energy of the samples where were extracted from a curved and edge region was lower than that of the samples where were extracted from a plane region.