2015 Vol.35(4)

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2015, 35(4): 0-0.
[Abstract](137) [PDF 4225KB](3)
Process and Properties of IN718 Formed by High-power Fiber Laser Melting
Jin-hui LIU, Bang-tao LIU, Xue-dong XIE, Xue-bing YUAN, Xiang-lin MENG
2015, 35(4): 1-7. doi: 10.11868/j.issn.1005-5053.2015.4.001
[Abstract](261) [FullText HTML] (48) [PDF 3654KB](2)
The influence of process parameters forming nickel-based superalloy IN718 by Selective Laser Melting(SLM) on the densification, microstructure and microhardness was studied. Four nickel-based superalloy IN718 samples were fabricated in various processing parameters using FORWEDO LM-180 SLM system. The samples were analyzed with Vickers hardness measurement, SEM and XRD. The results show that the increase of the laser energy density causes the decrease of porosity defects and the significant improvement of their relative density. Under higher laser energy density, microstructures grow more evenly and particles become finer. When the laser scanning speed increases, the laser radiation and cooling time get shorter, so the growing direction of microstructures is changed sharply. Complex heat transfer effects the complexity of the microstructure. Higher extent refinement of grain and densification improve the microhardness.
Determination of Undercooling Time for Stray Grain Formation of DD11 Single Crystal Superalloy
Yu-liang JIA, Li-li HE, Yun-song ZHAO, Hui-ming GUO, Xiang FANG, Jian ZHANG
2015, 35(4): 8-15. doi: 10.11868/j.issn.1005-5053.2015.4.002
[Abstract](223) [FullText HTML] (65) [PDF 3433KB](5)
The effects of platform size, site and withdraw rate on the formation of stray grain during the directional solidification of DD11 single crystal superalloy were investigated. The platform structure was designed to simulate the sudden change of plan area in single crystal blades. Based on the composition and microstructure observed with optical microscopy (OM) and the undercooling effect studied with differential thermal analysis (DSC), the critical undercooling time(ΔT/v) for stray grain formation was discussed. Results show that when the withdraw rate is 2mm/min, no stray grain is observed as the outer platform length ranges from 8mm to 26mm, whilst stray grain is formed when the length exceeds 18mm in inner platform. This suggests that larger platform size and inner position lead to stray grain formation. As the withdraw rate gradually increases to 6mm/min, stray grains are revealed in outer platform with various length, and only presented in inner platform with length more than 12mm. It is indicated that the increase of withdraw rate promotes the tendency of forming stray grain in both outer and inner platforms, while it shows more influence in outer ones. During directional solidification, the furnace temperature and cooling rate are influenced by platform size, position and withdraw rate, which lead to higher tendency of stray grain formation associated with small value of undercooling time.
Microstructure and Mechanical Properties of Underwater Friction Stir Welded 7A04-T6 Aluminum Alloy
Rui-qi XU, Wen WANG, Ya-xin HAO, Ke QIAO, Tian-qi LI, Kuai-she WANG
2015, 35(4): 16-21. doi: 10.11868/j.issn.1005-5053.2015.4.003
[Abstract](241) [FullText HTML] (50) [PDF 2283KB](3)
7A04-T6 aluminum alloy was welded by friction stir in the air and cooling water media respectively, and the effects of the forced cooling on the microstructure and mechanical properties of 7A04-T6 FSW joint were analyzed. The results show that the circulating cooling water has obvious instantaneous cooling effect, which significantly restrains the growth of grain recrystallization and precipitated phase. Average grain size and precipitated phase are 0.8μm and 30-150nm respectively in nugget zone under the condition of cooling water, both of which are smaller than the average grain size of 2.8μm and precipitated phase of 80-400nm under the condition of air cooling. Compared to the condition of air cooling, forced cooling significantly improves the mechanical properties of FSW joint. Average microhardness in nugget zone increases by 11.9HV, and tensile strength increases by 43.2MPa, which is 87.6% of that in base metal. Meanwhile, strain hardening capacity of FSW joint in cooling water also enhances, and the tensile fracture presents the characteristic of microporous polymeric fracture.
Cavitation Erosion on Surface of Pure Titanium in Water Cavitation Jet
Xiao-yang KAN, Peng-tao LIU, Mao-yang ZHOU, Xiu-juan ZHAO, Chun-huan CHEN, Rui-ming REN
2015, 35(4): 22-27. doi: 10.11868/j.issn.1005-5053.2015.4.004
[Abstract](162) [FullText HTML] (41) [PDF 2970KB](2)
Water Cavitation Jet(WCJ) of varied time was used on the surface of pure titanium under the pressure of 30 MPa. The surface morphology, microstructure and surface roughness of the test specimens were analyzed by optical microscope and scanning electron microscope after the WCJ treatment. The cavitation erosion on the surface of pure titanium was investigated at the same time. The results show that the damage zone is divided into the direct cavitating water jet damage zone and the mixed cavitating water jet damage zone according to the cavitation erosion damage degree and the characteristics of submerged water jet. In the direct cavitating water jet damage zone, some pits of plastic deformation, needle shaped cavitation erosion and twin of deformation appear on the surface of pure titanium in 5 minutes. With the increase of shot peening time (20-30min), cracks start to initiate and extend in the twin boundaries. A great deal of metal flakes off, and the surface roughness increases obviously in 60 minutes. The damage rate in the mixed cavitating water jet damage zone is significantly lower than that in the direct cavitating water jet damage zone, however, the twin layer of the mixed cavitating water jet damage zone is thicker and denser than that in the direct cavitating water jet damage zone in the cross-sectional microstructure. The hardening layer of the direct cavitating water jet damage zone is thinner than that of the mixed cavitating water jet damage zone. The fastest rising stage of the surface roughness is from 5min to 30min of cavitating water jet treatment. The rising rate of the surface roughness slows down after 30min and the surface roughness reaches 2.92μm after 60min.
Influence of Sputter Parameters on Optical Constants of SiNx Dielectric Film in D/M/D Structures
Yao SUN, Hong WANG
2015, 35(4): 28-33. doi: 10.11868/j.issn.1005-5053.2015.4.005
[Abstract](167) [FullText HTML] (47) [PDF 2453KB](2)
SiNx films were deposited by RF reactive magnetron sputtering as the dielectric layer in Ag-based transparent conductive films with D/M/D (dielectric/metal/dielectric) structure. The influence of power, pressure, and nitrogen flow on optical constants was investigated. The results show that the deposited film is amorphous. Its optical constants are in normal dispersion relation in the wavelength scale of 300-2500nm. Ellipsometry measurement and fitting by Cauchy model indicate that the refraction index decreases with the increase of power, pressure and N2 flow. The refraction index of 2.02 and extinction coefficient of 0 are obtained for SiNx film under optimum sputtered parameters (300W, 0.16Pa, and flow rate of N2 and Ar is 1:1), which is most close to the optical constants of Si3N4 film with a stoichiometric ratio. Finally, the SiNx film with the optimum thickness of 44nm is deposited under the optimum sputtered parameter as the dielectric layer of 20nm Ag film. The transmittance of Ag film increases from 29.17% to 55.01% when the selected SiNx is implemented as the upper layer, while the transmittance further increases to 66.12% when SiNx acts as both upper and lower layer.
Study on Structure, Heat Resistence Property and Electromagnetic Property of Quartz Fiber Rein-forced Polyimide Composite
Han-yang LIU, Wei-dong ZHAO, Ling-ying PAN, Chao CUI, Bao-gang SUN, Wen-ge JIANG
2015, 35(4): 34-38. doi: 10.11868/j.issn.1005-5053.2015.4.006
[Abstract](248) [FullText HTML] (71) [PDF 1160KB](4)
Quartz fiber rein-forced polyimide composite was fabricated by the autoclave process. The mechanical, thermal, and dielectric properties were tested at room-temperature and 350℃. The influence of the density, environment temperature and test frequency on the dielectric property were analyzed. The results show that the quartz fiber rein-forced polyimide composite presents excellent mechanical property at room-temperature and 350℃. Thermal conductivity is about 0.24-0.28W·m-1·K-1, thermal expansivity is 5.38×10-6/℃, and dielectric constant is 2.95-3.10, tanδ<8.0×10-3.
Low-velocity Impact Damage and Compression Failure Behavior of Plain Woven Composite Laminate
Shao-hua MA, Hong-jie GUO, Li HUI, Yong-gang WANG
2015, 35(4): 39-44. doi: 10.11868/j.issn.1005-5053.2015.4.007
[Abstract](212) [FullText HTML] (58) [PDF 3595KB](5)
Based on the low-velocity impact test and the compression test after impact on plain woven composite laminate at different impact energy, the relationships among the energy of impact, dent depth, damage area and residual compress strength were analyzed. The effect of different impact damage on the characteristic of compression failure through macroscopical observation at the side of the fracture on the compressed laminate was studied. Results show that impact damage includes non-damage, barely visible impact damage (BVID), visible impact damage (VID) and penetrating damage, and different damage grades have different failure characteristics. With the increase of impact energy, the dent depth increases gradually, but the relationship is not linear because of a knee point; the damage areas also increase gradually, and remain the same after reaching the penetrating damage; the residual compress strength decreases gradually. Finally both the damage areas and the residual compress strength tend to change slowly.
Tensile Failure Mechanism for Resin Matrix Composites Reinforced by Unidirectional Glass Fiber
Ji-liang ZHENG, Yong SUN, Ming-jun PENG
2015, 35(4): 45-54. doi: 10.11868/j.issn.1005-5053.2015.4.008
[Abstract](205) [FullText HTML] (66) [PDF 5913KB](4)
The commercial finite element software of ANSYS was used to establish the static axial symmetric plane model of Whitney and Riley for the resin matrix composites reinforced by unidirectional glass fiber. The effect of varied fiber aspect ratio on the mechanical property of the composite was analyzed by the non-liner finite element method, and the effect of the adhesion coefficient between fiber and matrix at the top and bottom on failure mode of the composite was also analyzed by the same method. Results show that the fiber aspect ratio has an optimum range. The composite shows no good property when the fiber aspect ratio does not reach a certain value, however, the property does not improve any further with the increase of the fiber aspect ratio when a certain value of the fiber aspect ratio is reached. With the increase of the adhesion between the fiber and interface at the top of the matrix, the largest absolute value of interfacial normal stress appears at the top of fiber. The normal interfacial stress at the top and bottom of fiber is turned into compressive stress, therefore, the fracture is near to the clamping upper end, and the clamping bottom end has no separation from the interface. With the increase of the adhesiont between the fiber and matrix at the bottom, the largest absolute value of the interfacial normal stress of fiber appears at the bottom of fiber. The interfacial normal stress at the top and bottom of fiber is turned into separating stress, thus the fracture is near to the clamping bottom end, and the clamping upper end shows the separation from the interface.
Simulation of Axial Crush Characteristic of Composite Sinusoidal Specimen and Analysis of Crashworthiness of Fuselage Section
Hao-lei MOU, Tian-chun ZOU, Yue-juan DU, Jiang XIE
2015, 35(4): 55-62. doi: 10.11868/j.issn.1005-5053.2015.4.009
[Abstract](257) [FullText HTML] (59) [PDF 4248KB](2)
Crashworthiness is one of the main concerns in aviation safety. The mechanical properties of T700/3234 were obtained by material performance tests, and the crushing energy-absorbing results of composite sinusoidal specimen were achieved by quasi-static axial crushing tests. The simulation results and test results were in good agreement, which could verify the correctness of finite element model and material model. A typical civil aircraft fuselage section with composite sinusoidal specimen under the cargo floor was developed, and the finite element model of fuselage section was built to simulate the vertical drop test subjected to 7 m/s impact velocity. The simulation results show that the established finite element model can accurately simulate the crushing process of composite sinusoidal specimen under the experimental conditions. The failure process of fuselage section with composite sinusoidal specimen under the cargo floor is more stable, and the acceleration subjected to occupants is limited to human tolerance, which is helpful to effectively improve the aircraft fuselage section crashworthiness.
Recent Progress in Study of Transparent Conducting Oxide Films
Hong-yan LIU, Yue YAN, Yong-lin WANG, Jian-hua WU, Guan-li ZHANG, Lei LI
2015, 35(4): 63-82. doi: 10.11868/j.issn.1005-5053.2015.4.010
[Abstract](292) [FullText HTML] (59) [PDF 3610KB](13)
Transparent conducting oxide films (TCOs), as indispensable components, have a significant number of application in solar energy batteries, flat panel displays and transparent windows, etc. This paper reviews present status and future prospects for the development of TCOs comprehensively, introduces the conducting and electron scattering mechanisms in TCOs and summarizes the material's selection rules for design of TCOs. Basically, the stoichiometric oxide film is non-conductive. However, this non-conductive oxide film can be transformed into conductive film by introducing some defects into the oxide film, e.g. oxygen vacancies, interstitials and exotic dopants, which form an energy level in these oxide films. According to the difference in type of defects, i.e., acceptor or donor, the transparent conductive oxide film can be classified into N-type and P-type semiconductors. Furthermore, in these defects induced conductive films, there are four scattering mechanisms including boundary scattering, phonon scattering, dopant scattering and twin boundary scattering. Amongst the aforementioned scattering mechanism, boundary scattering and dopant scattering are the two dominant scattering mechanisms in transparent conductive oxide films. Additionally, the properties and applications of impurity-doped In2O3-, SnO2-and ZnO-based TCOs are elaborated in detail. Owing to the advantage in preparation of low resistivity film and processing in semiconducting technology, the In2O3-based TCO is the most used material in preparation of transparent electrode, while the SnO2-and ZnO-based TCOs are the two most significant candidates for substitution of In2O3-based TCO because of their low cost. At last, combined with the development of multifunctional electronic devices, we propose that the transparent conducting film with oxide/metal/oxide sandwich structure is the future direction for improving the conductivity and transparency of TCOs.
Injection Molding Technology of Water-soluble Ceramic Core
Cheng-cheng WANG, De-long HE, Meng-ting JU, Jia-hu WEI, Xiao-su YI
2015, 35(4): 83-95. doi: 10.11868/j.issn.1005-5053.2015.4.011
[Abstract](304) [FullText HTML] (60) [PDF 1461KB](2)
Water-soluble ceramic core plays a key role in investment casting, especially the castings with complex inner cavity structures or high dimensional accuracy. This paper introduces recent research progress on the water-soluble ceramic core by injection molding technology systematically. A comprehensive review is made on the research advancement on the process and their influence on the microstructure, quality and performance of the water-soluble ceramic core. The key process includes plasticizers preparation, the choice of composition as well as particle sizes of inorganic salt binder and ceramic powder, mixing process, injection molding, degreasing and sintering, waterproof treatment, etc. This review provides technical guidance for the development of high performance water-soluble ceramic core. Finally, several main development trends of the water-soluble ceramic core in the future are concluded based on the previous analysis. In particular, emerging nano-material and technology as well as computer simulation technology will provide necessary support in the development of high performance and low cost core.

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