Papers by Author: Rui Fang Chen

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Authors: Rui Fang Chen, Hui Jiang, Yin Qun Hua, Yu Xiao Chen, Zhen Grong Cai
Abstract: The effect of laser shock processing (LSP) on bending fatigue performance of 7075-T651 aluminum alloy was studied. LSP was performed on fatigue testing specimens with optimized parameters. Stress-life fatigue data were generated for both shocked and as-machined conditions. The fatigue improvements of LSP were discussed accounting for the effect of residual stress. The results show that shocked specimens exhibited significantly improved fatigue performance, with as-machined specimens having a factor of 1.6-4.4 improvement in fatigue life (depending on fatigue stress level). The stability of the residual stress induced by LSP under cyclic load was particularly investigated by means of X-ray diffraction measurements. Residual stress relaxation was observed. And the higher the cyclic load, the higher the relaxation rate. Due to the cyclic creep effect, the residual stress decreases linearly with the logarithm of the number of cycles.
Authors: Yin Qun Hua, Zhen Rong, Kang Min Chen, Yun Xia Ye, Wen Hui Wu, Rui Fang Chen
Abstract: The oxidation behavior of Ni-based superalloy GH586 which is treated by pack-cementation aluminizing was investigated. Scanning electron microscope and X-ray diffraction were used to analyze the microstructure of aluminide coatings and the surface morphologies of the oxide scales. Results show that the main phase of the aluminide coatings was NiAl. The aluminide coating can be formed at lower temperature due to the addition of rare earth oxide in the mixture powders. The thickness of aluminide coating at 900°C was about 110μm, and another aluminide coating with rare earth oxide Y2O3 at 800°C was about 38μm. The oxidation kinetics of aluminized specimens approximately followed a parabolic oxidation law at 1000°C. The morphology of the oxidation scales was primarily θ-Al2O3 with minor α-Al2O3. The scales of the coatings with rare earth oxide Y2O3 after oxidation was more dense.
Authors: Yin Qun Hua, Zheng Rong Cai, Rui Fang Chen, Yu Xiao Chen, Hui Jiang
Abstract: The residual stress induced by Laser shock processing (LSP) can improve properties of fatigue crack growth. In this paper, the CT models of LSP and fatigue crack growth have been built. We experimented the TC4 alloy treated by LSP and fatigue crack growth and then simulated the fatigue crack growth. The results show that the values of simulations are conform to experiments. With the increment of peak pressures and overlapping rates, the fatigue lives have been increased, the fatigue crack growth rates have been descent. The fatigue lives have been 1.46-3.03 times compared with untreated by LSP, the fatigue crack growth rates have been 0.127-0.95 time compared with untreated by LSP, but to overlapping rates, it is not obvious with the improvement compared with peak pressures.
Authors: Rui Fang Chen, Yu Xiao Chen, Yin Qun Hua
Abstract: In order to improve the fatigue strength of TC4, Nd:Glass pulse laser was used to impact the surface of cylindrical specimens, X-ray stress analyzer was used to test the residual stress distribution of treated area, the laser shock processing on different ratio (η) between the diameter of specimens and laser spot were simulated with ANSYS at the same time. The numerical simulation results were well agreement with experimental data. The results indicate that the different η mainly affect residual stress distribution along the circumferential direction. Contrarily, it has few effects on longitudinal direction and in-depth direction.
Authors: Yin Qun Hua, Rui Fang Chen, Zhong Xiu Niu, Jie Yu
Abstract: Cu thin films were prepared by DC magnetron sputtering on Si substrate, and the resistivities change by adjusting its sputtering parameters. It is found that the changes of the sputtering power and substrate temperature and working pressure can affect significantly the Cu film resistivity (ρ). The Cu films resistivity decreases with the increasing of sputtering power. As the substrate temperature “structure zone model” effect, the Cu film resistivity decreases when the substrate temperature was less than 150°C. The resistivities (ρ) begin to increase gradually at various temperatures ranging from 150°C to 300°C, but the rate of increase is not significant. The resistivity abnormal increases when the substrate temperature was 400°C. The Cu films resistivity increases with argon working gas pressure ranging from 0.15 Pa to 2 Pa.
Authors: Yin Qun Hua, Yu Chuan Bai, Yun Xia Ye, Qing Xue, Hai Xia Liu, Rui Fang Chen, Kang Min Chen
Abstract: The paper aims to study the influence of high temperature processing on the substructure of laser shock processed titanium alloy. The titanium alloy specimens were first treated by laser shock processing (LSP), then treated at 700°C for three hours and air cooled to the room temperature to investigate the influence of the high temperature processing. To evaluate such influence, the hardness and substructure on the surface were investigated by micro hardness tester and transmission electron microscope (TEM), respectively. Results show that after three times LSP, the hardness of TC11 alloy was improved by 30.9%. The cause of such an improvement in hardness is that the crystal grains in the surface layer under the shock wave stress were strongly deformed, causing a dynamic recrystallization. The substructure is mainly twin crystals, highly tangled and dense dislocations. After high temperature processing in vacuum, the average hardness is decreased by 12% compared to that of the specimens after LSP. And the substructures are mainly small dislocation, nanocrystalline.
Authors: Rui Fang Chen, Yin Qun Hua, Hai Xia Liu, Yun Xia Ye
Abstract: This paper explores the properties of Fe40NiCrSiAl alloy treated by different methods. The hardness, elastic modulus and resistivity are tested. The results indicate that: after LSP to rolled Fe40NiCrSiAl alloy, the hardness increased 25.22%, the elastic modulus increased 7.17% and the resistivity decreased 39%. TEM photographs demonstrated that there appeared dislocations, martensite transformation and twin crystals inside the material after being treated by LSP. Twin crystals are the main reason attributing to the improvement of material electrical properties.
Authors: Rui Fang Chen, Yin Qun Hua, Yun Xia Ye
Abstract: Fe20Ni3Mn alloy is treated by LSP. The hardness, residual stress and microstructure in the strengthened zone are studied. The results show that the hardness of the strengthened surface is increased about 15% and the surface compressive residual stress is reached about -469MPa. There exist martensite transformation and dislocation within 1mm depth from the specimen surface. Some martensitic structures have obvious trend of growth in steps. Specially, the twin crystals in martersite induced by LSP have important application.
Authors: Rui Fang Chen, Yin Qun Hua, Guang Ji, Zhen Zhen Sun
Abstract: In order to improve electrical properties, annealed ZnO varistor ceramics have been treated by laser shock processing (LSP). Electrical parameters of the annealed ZnO varistor ceramics were measured by CJ1001 Varistor Tester. Morphology and microstructure of the annealed ZnO varistor ceramics were gained by XRD and SEM. The results indicate that compared with the electrical properties of the annealed ZnO varistor ceramics, the voltage gradient of the ZnO varistor ceramics treated by LSP remains the same, the nonlinear coefficient substantially increases by 31.6%, and the leakage current reduces by 33.3%. Meanwhile, the phase composition of the annealed ZnO varistor ceramics is mainly composed of ZnO main phase, Zn2.33Sb0.67O4, β-Bi2O3, and δ-Bi2O3 phase; while the phase composition of the ZnO varistor ceramics remains the above four phases in the compound state (anneal and then LSP), but the content of δ-Bi2O3 phase increases. The increase of δ-Bi2O3 phase content is the main reason for improving the electrical properties of the annealed ZnO varistor ceramics.
Authors: Yin Qun Hua, Jie Yu, Rui Fang Chen, Cheng Chen, Rui Li Xu
Abstract: Nanocrystalline ZnS thin films are prepared on glass substrates under various deposition conditions (radio frequency power, and sputtering pressure) using radio frequency magnetron sputtering at room temperature. Through optimization of deposition process, very thin and uniform ZnS layer was deposited to minimize the light blocking effect in short wavelength region. This paper investigates the influence of ZnS buffer layer by magnetron sputtering,and analyses structure,surface topography,and optical properties of ZnS films by using X-ray diffraction (XRD), UV-spectroscopy measurements and scanning electronic microscope (SEM) analysis techniques. Findings show that the high-quality ZnS thin films with a good crystallinity and optical properties, which is zinc blende cubic structure with a preferred orientation, can be grown by sputtering at 300W and 0.6Pa. The films exhibit the optical transparency as high as 80% in the visible region, and the resultant ZnS thin films have a high crystallinity, low defect concentration and good optical properties with the band gap of 3.50eV.
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