Papers by Author: Yi Xiong Wu

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Authors: Xian Cheng Zhang, Bin Shi Xu, Hai Dou Wang, Yi Xiong Wu
Abstract: The effect of NiCoCrAlYx-ZrO2 (1-x) interlayer on the residual stresses in the ZrO2/NiCoCrAlY thermal barrier coating due to thermal cycling was analyzed using the finite element method. Modeling results showed that the magnitude and distribution of the residual stresses in the coating were strongly influenced by the material combination characterized by the value of x and the thickness of interlayer. The maximum tensile stresses at the different regions (i.e. coating/substrate interface, coating surface, et al.) as functions of the material combination and the thickness of the interlayer were obtained. The physical meaning of the above results was also discussed.
Authors: Zhu Guo Li, S. Miyake, Yi Xiong Wu
Abstract: This article summarizes briefly our recent research on low-temperature synthesis of TiN, TiN/Cu and TiN/Si films by using inductively coupled plasma assisted magnetron sputtering method. It is shown that the incorporation of high-flux low-energy ion irradiation during deposition strongly affects film growth, structure evolution, morphology and mechanical properties. A main attention is devoted to the synthesis of superhard nanocomposite films at a low deposition temperature. In both TiN/Cu and TiN/Si films the maximum hardness reaches a value higher than 40 GPa.
Authors: Zhi Guo Gao, Jian Huang, Yi Xiong Wu
Abstract: For many years, rivet joint technology has been applied in the automotive and aerospace industry. Recently, it began to apply laser welding technology to lap joints instead of rivet joining. Laser spot welding has some potential advantages including time saving, cost reduction, material saving and weight reducing. A lap joint of aluminum alloy LY12 with different plate thickness, namely 2mm and 1mm, was spot-welded by CO2 laser. For the welding, laser power in pulse form with ramping-up and cooling-down shape was used, and pure helium gas served as shielding gas to fill around welding area. In this study transient three-dimensional non-linear finite element modeling was used to analyze heat flow and residual stress of the laser spot welding of aluminum alloy LY12. In modeling the temperature dependence of material properties, influence of contact surfaces are taken into account. To analyze, Gaussian distributed heat source model and thermo-elasto-plastic behavior were applied. Weld dimensions and residual stress at the weld surface were calculated numerically and compared with the experimental results.
Authors: Yong Zhao, Jian Huang, Ying Zhao, Yi Xiong Wu
Abstract: Microstructures and mechanical properties of welded Ti-6Al-4V alloy lap joints are discussed under different parameter conditions of laser welding. The results reveal that the fusion zone consists mainly of acicular α'martensite. The shear strength of the lap joint reaches a maximum of 836MPa at a laser power of 4kW and welding speed of 2.3m/min. When the laser power is 4kW and the welding speed is 2.1m/min, microstructures of weld joint become coarse and the shear strength falls to 736MPa. The microhardness value in the weld zone is the highest and it gradually reduces from the weld center to base metal due to the difference of microstructure. When the weld heat input is constant, larger laser power has resulted in growth of the grain and the decrease of shear strength and microhardness of lap joints.
Authors: Lian Hai Hu, Qi Yan, Jian Huang, Yi Xiong Wu
Abstract: Reducing car’s weight has become an important goal for automobile industry. Laser welding of automotive high-strength steel plays a significant role in producing light weight cars. Experiments of CO2 high power laser welding of 1000MPa grade complex phase steels with a thickness of 3mm for automobile were performed using a 15 KW CO2 laser. The macrostructure and microstructure of the welded joint were examined by optical microscope. Mechanical properties of the welded joint, fusion zone and base metal were assessed by microhardness distribution across the welded joint, uniaxial tensile test and charpy V-notch impact test. Fractographs of the impact specimens were studied by scanning electron microscopy (SEM). It is found that the fusion zone has a higher toughness than that of the base metal and fusion line. The test results show good mechanical properties of laser welds that can meet the technical requirements for automobile Industry.
Authors: Xian Cheng Zhang, Bin Shi Xu, Hai Dou Wang, Yi Xiong Wu
Abstract: The purpose of the present paper was to investigate the effect of interlayer on the maximum contact stresses in the critical regions in a hard coating under static contact condition using finite element analysis. Four different elastic moduli and nine different thickness of interlayer were used. Modeling results showed that the interlayer did not reduce the maximum shear stress at the coating/substrate interface, whether it was thick or thin. When the thin interlayer was presented, whether it was soft or hard, the maximum tensile stress on surface and maximum von Mises stress within coating were decreased.
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