LUO Chen, CAI Jian-ping, CHEN Ya-zheng, LIU Ming, ZHAO Liang-liang, SUN Zhi-hua, TANG Zhi-hui, LU Feng. Effect of Applied Strain on Protective Properties of Aviation Organic Coatings[J]. Journal of Materials Engineering, 2014, 0(5): 1-6.
A method of pre-strain application on strip coating specimens was introduced. The strain of organic coating was quantitatively measured by microscopy observation of original mark on the coating. Outdoor exposure of the strip organic coating specimens with various strain was carried out, which realized the combination of natural environmental effect and mechanical effect. Therefore, the protective properties of organic coating in real service state can be more precisely evaluated. The result shows that the electrochemical impedance of zinc yellow acrylic polyurethane coating without pre-strain is gradually reduced from 1.8×109Ω to 4.7×105Ω in 36 months of outdoor exposure in Wanning. Electrochemical impedance modulus of coating specimens with either compressive pre-strain or tensile pre-strain decreases after outdoor exposure. However, coating specimens with tensile pre-strain exhibit more significant decrease than those with compressive pre-strain in electrochemical impedance, indicating the tensile pre-strain has a great effect on protective properties of organic coatings.
YAN Biao, WEN Li-wei. Hot-press Bonding for Prepreg in Automatic Placement and Tape Winding[J]. Journal of Materials Engineering, 2014, 0(5): 7-11.
The hot-press fast-bonded model was deduced using fluid mechanics. Influence of main parameters, such as hot-press pressure, hot-press temperature, hot-press time, etc, on bonding capability was analyzed. The hot-press bonding experiments were carried out to analyze the factors of pressure, temperature, time and lap length for glass fiber fabric/phenolic resin prepreg(664/B30). The results show that the bonding performance of prepreg increases with the increasing of pressure, temperature, time and lap length, and which agrees with theoretical prediction well.
HU Zhen-feng, LYU Biao, WANG Xiao-he, XU Bin-shi. Effect of Relative Moving Speed on Microstructure and Properties of Brush Electroplating Nickel[J]. Journal of Materials Engineering, 2014, 0(5): 12-16.
A novel bore brush electroplating technology was applied in remanufacturing for internal surface of failed engine cylinder body. The effect of relative moving speed on microstructure and properties of automatic brush electroplating nickel was investigated by SEM, XRD, TEM, microhardness tester and CETR friction and wear testing machine. The plating was compared with traditional Watts Ni plated. The results show that nickel plated coatings are face center cubic structure. Electroplated Ni has coarse surface and (200) preferential orientation from the Watts bath while brush electroplated nickel has compact and smooth microstructure, and (111) preferential orientation, without pinholes and nodules defects. With relative moving speed increasing from 0.25m/s to 1.00m/s, the degree of brush electroplated Ni (200) preferential orientation gradually decreases and that of (111) preferential orientation increases; the microhardness increases from HV420 to HV600, and mass loss decreases from 8.7mg to 6mg.
LIU Ming-tao, ZHONG Xi-chun, LIU Zhong-wu, ZENG De-chang, LI Zhou, ZHANG Guo-qing. Structure and Properties of MoSi2-CoNiCrAlY Nano-composite Coating by Plasma Spraying[J]. Journal of Materials Engineering, 2014, 0(5): 17-22.
MoSi2-CoNiCrAlY composite coating was deposited on superalloy GH4169 substrate with ball milled nanocrystalline powders by plasma spraying technology. The phase constitution and microstructure of the nano-composite feedstock and coating were analyzed by X-ray diffraction (XRD), laser particle size analyzer and scanning electron microscopy (SEM). The properties such as microhardness, thermal shock resistance and low-temperature oxidation behavior of the coating were also studied. The results show that the milled powder is composed of small nanocrystalline polycrystals which can be used directly for thermal spraying after sieving slightly. The as-sprayed coating is metallurgically bonded with the substrate and has compact structure and low porosity. The microhardness strictly fits into the Weibull distribution, and the average values of microhardness and lifetime of thermal shock failure are 854.4HV0.1 and 27 cycles, respectively. After oxidized at 500℃ for 120h, the coating has only a small mass increase of 0.083mg/cm2, and the "pesting" phenomenon of MoSi2 does not occur.
ZHANG Xiao-feng, YU Lei, YANG Zhen-xiao, DENG Chun-ming. High Thickness Tungsten Coating with Low Oxygen Content Prepared by Air Plasma Spray[J]. Journal of Materials Engineering, 2014, 0(5): 23-28.
Irregular tungsten powders were spheroidized by air plasma spray (APS). Using reduced spheroidized powders, graded tungsten coatings with Cu-Mo/Mo-W bond coating were prepared on CuCrZr alloy under the protection of nitrogen by air plasma spray. The phase and microstructure of tungsten powders and coatings were analyzed by XRD and SEM. The oxygen content, thermal conductivity and bonding strength of coatings were measured by O/N tester, laser thermal conductivity instrument and tensile testing machine respectively. The chemical valence state of tungsten in the coating was investigated by XPS. Results indicate that the tungsten coating with thickness of about 2mm can be prepared successfully, and its average bonding strength is 15.2MPa. Compared with vacuum heat treatment, reduction of H2 can evidently decrease the oxygen content of spheroidized tungsten powder and coating. After reduction of H2, the oxygen content of tungsten coating decreases from 0.93% (mass fraction) to 0.17%. During spray process, it consists of convection and diffusion oxidation. So the tungsten coating has trace amounts of oxide in it, which mainly contains WO2.72 and WO3.
XIN Xing, ZHANG Xin-ming, LIU Sheng-dan, SONG Feng-xuan, CHEN Bin. Effect of Pre-aging Temperature in Retrogression and Re-aging Treatment on Stress Corrosion Resistance of 7050 Aluminum Alloy[J]. Journal of Materials Engineering, 2014, 0(5): 29-34.
The effect of the pre-aging temperature in retrogression and re-aging (RRA) treatment on stress corrosion resistance of 7050 aluminum alloy was investigated by means of hardness tests, conductivity tests, slow strain rate tensile (SSRT) tests, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that when the pre-aging temperature increases, the main intragranular precipitates in 7050 aluminum alloy transform from GP zones to η' phases after RRA. The grain boundary precipitates become coarser and consequently the grain boundary becomes discontinuous, which leads to the reduction of sensitivity of stress corrosion. At the meantime, the precipitate free zone (PFZ) becomes wider, whose width goes up to 140nm when pre-aging temperature rises to 120℃,causing stress concentration and anode dissolution which are harmful to the stress corrosion resistance of the alloy. When the pre-aging temperature is 80℃, as in under-aged condition at the pre-aging stage of RRA, the alloy shows better stress corrosion resistance. The tensile strength, elongation and stress corrosion index (ISSRT) of the alloy are 473.5MPa, 10.67% and 0.05824 with slow strain rate (10-6s-1) and corrosion medium of 3.5%NaCl solution.
WANG Jing-feng, LI Lin-jun-nan, LU Ruo-peng, PAN Fu-sheng. Influence of Structure on Vibration Damping Capacity of Deformation Magnesium Alloy[J]. Journal of Materials Engineering, 2014, 0(5): 35-39.
The finite element simulation method was used to study the instantaneous dynamic response in the same excitation for AZ31 magnesium alloy profiles with different reinforcing plate. According to the excitation response characteristic of AZ31 magnesium alloy profiles, the vibration damping performance was evaluated. The results show that the magnesium alloy profiles with triangle reinforcing plate have a better damping performance than the magnesium alloy with rectangular reinforcing plate. The vibration experimental research was used to study the damping performance of the magnesium alloy profiles with triangle reinforcing plate and rectangular reinforcing plate. Experimental results indicate that the simulated conclusion is consistent with the experiment. In order to explain the research results that magnesium alloy profiles with rectangular reinforcing plate had a low quality in damping performance, the improvement optimization scheme was put forward. The subsequent simulation results show that the section deformation and stress performance of the AZ31 magnesium alloy profiles are all effectively improved as expected.
YU Qiang, CHEN Zhen, FAN Ying-ying, WEI Chang, LIANG Mei-yan, WEN Da-kai. Influence of Nano-ZrO2 on PbO2-CeO2-ZrO2 Anode Materials[J]. Journal of Materials Engineering, 2014, 0(5): 40-45.
The inert anodes material PbO2-CeO2-ZrO2 was prepared by using composite electrodeposition for trivalent chromium plating. Deposition mechanism, corrosion resistance and catalytic activity of electrode materials were analyzed by using electrochemical measurement methods. The micro-morphology and elemental content of electrode materials were studied by SEM and EDS. The results show that the deposition of the coating accords with Johnson mechanism, the deposition process of PbO2 is very stable. The inert anode material has good corrosion resistance, high catalytic activity when ZrO2 concentration is 20g/L in bath. The influence of nano-ZrO2 for micro-morphology is not obvious, with the ZrO2 content increasing in the bath, the CeO2 content is stable and the ZrO2 content increases first and then decreases in coating.
ZHANG Jun-jun, SANG Yan-xia, YE Jian-shan, LI Wen-fang. Influences of Substrate Pretreatments on Anticorrosion Properties of Rare Earth Conversion Coatings[J]. Journal of Materials Engineering, 2014, 0(5): 46-52.
To optimize the preparation process and anticorrosion properties, the conversion coatings were prepared with different pretreatment processes. The influence of pretreatment processes on anticorrosion properties of conversion coatings was investigated via salt spray test. Two optimal pretreatment processes (4# and 8#) were obtained. Measurement of polarization curve and electrochemical impedance spectra (EIS) was used to study the corrosion resistance of film on Al alloy in 3.5% (mass fraction) NaCl solution. The morphology, elemental composition and wetting angle of the surface of uncoated and coated film after pretreatment were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and wetness angle measuring instrument, respectively. The conversion coatings forming speed, surface hardness and tribological property were investigated by means of eddy current thickness meter, microhardness tester and frictional wear testing machine. The results show that the pretreatment significantly affects the thickness, the completeness and the density of film by means of the wetting ability and negative points distribution of surface and also affects the corrosion resistance of conversion coatings. The research results show that 8# is an optimal pretreatment.
MAO Ping-li, XI Tong, LIU Zheng, DONG Yang, LIU Zun-xin, DI Jin-nan. Dynamic Mechanical Property of AZ31 Magnesium Alloy Welding Joint Under High Strain Rate[J]. Journal of Materials Engineering, 2014, 0(5): 53-58.
The dynamic compression test was carried out for rolled AZ31 magnesium alloy welding joint of argon tungsten-arc welding (TIG) and friction stir welding (FSW) with the split Hopkinson pressure bar at the strain rates of 900-2500s-1. The microstructure and fracture mechanism of the specimens were analyzed by scanning electron microscope (SEM) and optical microscope. The results show that with the increasing of the strain rate, the true stress-strain curves of AZ31 magnesium alloy welding joint have little change, implying the stress of AZ31 welding joints is not sensitive to the strain rate. The strength and plasticity of FSW joint are better than those of TIG joint under high strain rate. The fracture mode of AZ31 welding joints is cleavage under high strain rate, but compared to TIG joint, the FSW joint fracture is more smooth. The deformation microstructure analysis demonstrates that the microstructure is not sensitive to the strain rate, and the deformation mechanism of AZ31 welding joints is slipping under high stain rate compression.
SHAN Hang-ying, XIAO Jun, LI Ning, SHANG Wei, ZHANG Xiang-yang. Experiment and Analysis on Shear Modulus of X-cor Sandwich[J]. Journal of Materials Engineering, 2014, 0(5): 59-65.
An analytical formula was derived for the shear modulus of X-cor sandwich structure based on mechanical analysis of tensile and compressive stress in Z-Pins. By comparing results from test and calculation, the modified theoretical formula of shear modulus was achieved concerning stiffness discount factor M. The results show that the stiffness discount roots in Z-Pin being pulled from face skin under load. Higher stiffness discount factor M can be obtained by bettering the craft, including decreasing Z-Pin length difference or elevating the pull-out force of Z-Pin, and then sandwich shear modulus can be further improved.
HE Qing, QU Yi, WANG Rui-jun, WANG Wei-ping. Gas Hot-corrosion Resistance of Nanostructure and Segmentation Thermal Barrier Coatings on DZ40M Superalloy[J]. Journal of Materials Engineering, 2014, 0(5): 66-72.
The NiCrAlY bond coating was prepared by high velocity oxygen-fuel spray(HVOF) on the surface of directionally solidified DZ40M Co-based superalloy, and nanostructure and segmentation structure 7YSZ top coating were prepared by atmosphere plasma spray(APS) from nano-agglomerated powder. Gas hot-corrosion resistance of DZ40M alloy and alloy with different structure thermal barrier coatings(TBCs) at 900℃ was studied. Corrosion products and corrosion process were analyzed. The results show that DZ40M alloy with TBCs has more excellent gas hot-corrosion resistance than that of the alloy without coating, and avoid many easily detached corrosion products and corrosion voids in DZ40M alloy under gas hot-corrosion process. The coatings with different structure remain intact after gas hot-corrosion, and hot corrosion rate is almost appropinquity of DZ40M alloy with two kinds top coating. The coating with segmentation crack can prolong strain tolerance and thermal cycle life, but the vertical cracks are unable to become a passage for corrosive medium rapid infiltration.
CAI Deng-an, ZHOU Guang-ming, WANG Xin-feng, QIAN Yuan, LIU Wei-xian. Mechanical Behavior of Bidirectional Glass Fiber Fabric Composites Subjected to Biaxial Tensile Loading[J]. Journal of Materials Engineering, 2014, 0(5): 73-77.
To study the behavior of bidirectional glass fiber fabric composite under complex stress states, biaxially loaded cruciform specimen was designed and a series of tests under biaxial tensile loading at different load ratios were implemented. Comparison and analysis were carried out for the biaxial tensile modulus, tensile strength and failure mode of the material. The result shows that the uniaxial tensile behavior of the composites exhibits nonlinear at the later period and brittle fracture, and the nonlinear phenomena under biaxial loading are more significant. The biaxial tensile modulus rises with the increase of loading. The biaxial stretch has strengthening effect on tensile modulus to a certain extent. However, the biaxial weakening effect of the material is remarkable, and the biaxial tensile strength of the material is only 60.5% of the uniaxial strength at equal proportion extension. Moreover, the failure occurs in the center of the test area. The failure modes of the material at different load ratios are slightly diverse, which respectively shows fiber breakage, matrix failure and fiber cloth delamination.
SUN Tao, LIANG Jin, GUO Xiang, LI Lei-gang, REN Mao-dong. Anisotropy Measurement and Investigation on Cu/Al Clad Metals After Prestrain Based on Digital Image Correlation[J]. Journal of Materials Engineering, 2014, 0(5): 78-85.
To measure the deformation of Cu/Al clad metals made by explosive welding technique,a new full-field three-dimensional deformation measurement method was proposed and implemented based on the digital image correlation(DIC) method and binocular stereovision. To validate the feasibility of the proposed method, an extensometer was used during the Q235 steel tensile test. The anisotropy of Cu/Al clad metals under uniaxial tension after prestrain was investigated. The results demonstrate that the accuracy of strain measurement is not lower than 0.5%, much close to that of the extensometer. With an increase in prestrain, the anisotropy of Cu/Al clad metals mechanical parameters increases first and decreases afterwards. The plastic strain ratio, strain hardening rate all strongly depend on loading directions and prestrains. The linear relations between longitudinal strain and transverse strain are also influenced by tensile directions and prestrains.
MA Zhi-yuan, LUO Zhong-bing, LIN Li. Characterization of Ultrasonic Longitudinal Velocity Evolution in TBCs with Different Porosity and Void Morphology Based on Random Void Model[J]. Journal of Materials Engineering, 2014, 0(5): 86-90.
To describe the non-uniform microstructure of ZrO2-7% (mass fraction) Y2O3 deposited by EB-PVD, a novel YSZ random void model (RVM) was proposed based on the random media theory and statistical analysis method. The ultrasonic testing of YSZ coatings, whose porosities were 0%, 5% and 10%, respectively, were simulated with finite difference time domain (FDTD) method. The variation of the longitudinal wave velocity caused by the porosity and void morphology was analyzed. Results show that the velocity decreases with the increase of porosities in YSZ coatings. In the case of 5% and 10% porosity, the decreased values are 14.4% and 23.9%, respectively, compared with that of the dense coating. Furthermore, the corresponding velocity fluctuations caused by the difference of void morphology are 5% and 6.8%, respectively, which match with 5.9% and 7.5% of experimental results.
ZHOU Zhuo-hui, HUANG Da-qing, LIU Xiao-lai, MOU Wei-qi, KANG Fei-yu. Application Developments of Metamaterials in Wideband Microwave Absorbing Materials[J]. Journal of Materials Engineering, 2014, 0(5): 91-96.
The development process of metamaterial used as radar absorber and its current research situation were reviewed. Especially, the different ways of extending radar absorbing bandwidth of metamaterials were discussed on the basis of different absorbing mechanism, which included resonance absorption, loading lumped components and loading resistance materials. The adjustable metamaterial was also an option to achieve intelligent absorption and broadband absorption.The fractal curve and fractal pattern in metamaterials absorber design which can resonate at low frequency in small size footprint were discussed, at the same time the fractal pattern's band expansion capabilities was an upmost important merit to gain wider bandwidth. According to those advantages, the fractal curve and the fractal pattern design is concerned as prospected structures to achieve perfect wideband absorption in the future.
