## 2018 Vol.38(3)

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2018, 38(3): 0-0.
[Abstract](394) [FullText HTML] (277) [PDF 937KB](19)
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2018, 38(3): 1-9. doi: 10.11868/j.issn.1005-5053.2018.001010
[Abstract](370) [FullText HTML] (158) [PDF 1044KB](26)
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High temperature microwave absorption material is significantly important to improve the viability of advanced weapon and equipment. This paper summarizes the research progress of high temperature microwave absorption materials. The current research status of SiC based oxygen-free ceramic materials, laminated ternary ceramics (MAX phases), carbon materials and metal oxides, including the methods of manipulating the electronic structure, doping, designing multilayer structure and designing porous structure to improve their absorption properties, together with the related mechanism is discussed. Oxidation and unclear mechanisms for microwave absorption performance at high temperature are the main problems in the present research of high temperature microwave absorption materials. Finally, the trend of developing applied research and designing smart high temperature microwave absorption material is also prospected.
2018, 38(3): 10-19. doi: 10.11868/j.issn.1005-5053.2018.001009
[Abstract](658) [FullText HTML] (233) [PDF 2130KB](28)
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As a novel structural material proposed by topology optimization, metamaterials present unusual properties, such as negative Poisson’s ratio, negative indexofrefraction and so on. Metamaterials have potential application in the aspect of wave controlling and stealth. Therefore, it has aroused great interests in the world. Additive manufacturing technology, also called 3D printing technology, is suitable to make structures with complicated geometries. It is a high geometric freedom to fabricate stealth metamaterials via additive manufacturing technology, which provides technical support for the wide applications. The design of structure and the theory of stealth are both mentioned based on the basic theory of metamaterial. Moreover, a variety of additive manufacturing processes for the preparation of stealth metamaterials, such as light curing method, fusion deposition method, laser selective sintering / melting method are described in detail in the present paper. Problems, for instance, the staircase effect, raw material adhesion, thermal diffusivity, dimensional accuracy and roughness occurred in the fabrication of additive manufacturing metamaterials are discussed in order to provide references for the follow-up researchers.
2018, 38(3): 20-25. doi: 10.11868/j.issn.1005-5053.2018.000030
[Abstract](296) [FullText HTML] (124) [PDF 2148KB](15)
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The 7050 aluminum alloy samples were prepared from as-atomized 7050 aluminum alloy powder through cryomilling, hot isostatic pressing, hot extrusion and T6 heat treatment. The influence of cryomilling on morphology, grain size and microscopic strain of aluminum alloy powder were analyzed by SEM and XRD. The influence of cryomilling on microstructure and mechanical property of the sample after heat treatment was analyzed by OM, EBSD, TEM, XRD, microhardness and tensile test. The results show that cryomilling can effectively refine the grain size of the material and increase the number of nano-precipitates in the matrix. Compared to the as-atomized powder, the mechanical properties of the 7050 aluminum alloy sample prepared by cryomillied powder are obviously improved.
2018, 38(3): 26-30. doi: 10.11868/j.issn.1005-5053.2017.000093
[Abstract](277) [FullText HTML] (103) [PDF 2238KB](10)
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The low oxygen content SiC fibers were exposed in simulated aeroengine circumstance of \begin{document}${P_{{{\rm{H}}_2}{\rm{O}}}}:{P_{{{\rm{O}}_2}}}:{P_{{\rm{Ar}}}} =$\end{document}14 kPa \begin{document}$:8$\end{document} kPa \begin{document}$:78$\end{document} kPa at 1200 ℃ for 1-50 h. Performances and structure of the fibers were characterized by element analysis, XRD, SEM and tensile test. The results show that the fibers have higher oxygen content, thicker oxide layer, lower strength compared with the fibers treated in dry air. Cracks and α-SiO2 crystal are more likely to occur in silica layer. The steam in the simulated circumstance can accelerate oxidation and crack formation in silica film.
2018, 38(3): 31-39. doi: 10.11868/j.issn.1005-5053.2017.000167
[Abstract](289) [FullText HTML] (117) [PDF 3947KB](18)
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The mechanical and high-temperature dielectric properties of SiCf/SiC composites with nano-SiO2 filler were investigated in the present work for the development of high-temperature structural microwave absorbing materials. The results reveal that the flexural strength of SiCf/SiC composites is increased firstly and then is degraded with the filler content increased from 3% to 15%, and the maximum strength can be up to 275 MPa, meanwhile all of which show favourable fracture toughness. Owing to the high specific surface area and low permittivity of SiO2 filler, the complex permittivity of the composites decreases and the room-temperature reflection loss (RL) is promoted with the increase of filler content. When the composites possess 15% SiO2 filler, the room-temperature RL values can be reached to –8 dB in the whole X band with the thickness of 3.2-4.0 mm. The complex permittivity of the composites increases with the rising temperatures, while the specific values and increasing range of the high-temperature complex permittivity can be significantly reduced by introducing the SiO2 filler, and the composites can obtain excellent microwave absorbing property at 700 ℃ with the thickness range of 2.7-3.0 mm.
2018, 38(3): 40-45. doi: 10.11868/j.issn.1005-5053.2017.000207
[Abstract](460) [FullText HTML] (187) [PDF 4881KB](19)
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HIPed FGH96 superalloy prepared by AA powder was used as the research object, and the PPB precipitations and microstructures before and after different hot deformations were studied. The results show that PPB precipitates with circular distribution can be seen in HIPed FGH96 superalloy, and the coarse strip prime γ′ phase with circular chain distribution is one of the main characters of PPB. After hot deformation, the PPB in FGH96 superalloy is deformed and broken, the recrystallization grains are refined and twisted, and the grain misorientation becomes smaller. With the increase of deformation temperature and hot deformation, and the decrease of deformation rate, the deformation and fragmentation of PPB precipitates are more significant, the size of the primary residual γ′ phase becomes smaller, and the volume becomes less. The increase of deformation temperature and hot deformation, and the decrease of deformation rate are beneficial to reduce or even eliminate PPB precipitations.
2018, 38(3): 46-51. doi: 10.11868/j.issn.1005-5053.2017.000172
[Abstract](307) [FullText HTML] (84) [PDF 2359KB](11)
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K4536 alloy formed by SLM was treated by HIP, and the effects of HIP on the microstructure and high-temperature mechanical properties were studied. The results show that the surface of sample manufactured by SLM has cracks, and the longitudinal and horizontal microstructures are different. After HIP processing, the cracks in the sample is repaired to some extent, the microstructure of the sample also is changed, and many second phase particles are dissolved out from the matrix. We know that the precipitation is M23C6 phase by TEM diffraction analysis. Furthermore, the surface of sample has " white bright layer” with the thickness of about 30 μm, the " white bright layer” is resulted by the decrease of Cr by EDS energy spectrum analysis. The K4536 alloy sample formed by SLM has different high-temperature tensile properties in the vertical and horizontal, and the vertical performance is better than that of horizontal. After HIP processing, the vertical and horizontal performances have little difference, and the high-temperature strength of the sample is reduced, the high-temperature plasticity is increased.
2018, 38(3): 52-57. doi: 10.11868/j.issn.1005-5053.2017.000205
[Abstract](450) [FullText HTML] (122) [PDF 2354KB](8)
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The influences of withdrawal rate and mold heater zone temperature during high rate solidification (HRS) on the microstructures were investigated. As the results, the primary dendritic spacing, the size of γ′ phase particles and carbides are decreased with the increase of the withdrawal rate or mold heater zone temperature. As the withdrawing goes on, the primary dendritic spacing and the size of γ′ phase particles are increased, and the heat emission efficiency of HRS process is decreased. The results show that fine dendrite and γ′ phase can be achieved with the withdrawal of 8 mm/min and mold heater zone temperature of 1520 ℃/1530 ℃, which is benefit to improve the properties of DZ466 alloy.
2018, 38(3): 58-64. doi: 10.11868/j.issn.1005-5053.2018.000014
[Abstract](293) [FullText HTML] (91) [PDF 1133KB](12)
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Low cycle fatigue (LCF) tests were conducted on a single crystal nickel-based superalloy DD6 with crystallographic orientations [001] at different elevated temperatures. The typical temperatures selected are 600 ℃, 650 ℃, 700 ℃ and 760 ℃, which represent the temperature field of turbine blade root or dovetail. The experimental results indicate that the characteristic of cyclic hardening exists in DD6 superalloy at middle temperature range. The LCF strain range-life curves are temperature-dependent. A modified cyclic damage accumulation (CDA) life prediction model is proposed. In this modified model, an approximate logarithmic linear function is introduced as the additional terms to consider the temperature effect. The prediction results are mainly distributed in scatter band of ±3. The temperature-modified CDA models agree well with the experimental data.
2018, 38(3): 65-71. doi: 10.11868/j.issn.1005-5053.2017.000081
[Abstract](247) [FullText HTML] (87) [PDF 3199KB](8)
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To improve the corrosion resistance and load-bearing performance of titanium alloy, the TiC/Ti based composite coating with good metallurgical quality was prepared on the surface of TC4 titanium alloy by using Diode laser, and the effect of TiC content on the microstructures and properties of TiC/TC4 cladding was studied. The microstructure and phase constitution of the coating were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD), the micro-hardness, corrosion resistance and the load-bearing performance of the coatings were evaluated. The results show that the cladding consists of TiC, TiC0.95, NiTi2 and α'-Ti, and the overall hardness of the coating fluctuates greatly. The micro-hardness in hard phases and in the heat affected zone are 1000-1500HV and about 437HV respectively. While the mass fraction of Ni coated TiC is not higher than 60%, higher corrosion resistance of claddings can be obtained with the increase of the mass fraction of Ni coated TiC, reaching a maximum at 60%; while the mass fraction of Ni coated TiC is not higher than 50%, the load-bearing capacity of claddings can be improved with the increase of the mass fraction of TiC, reaching a maximum at 50%.
2018, 38(3): 72-76. doi: 10.11868/j.issn.1005-5053.2017.000208
[Abstract](254) [FullText HTML] (84) [PDF 1821KB](8)
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The fatigue crack growth behaviors of Ti-6.5Al-2Zr-1Mo-1V titanium alloy at different positive stress ratios (R = 0.1, 0.3 and 0.5) were investigated at room temperature. The effects of stress ratio R on the fatigue crack growth rates and fractures morphology were discussed. The results show that with the increase of stress ratio R , the fatigue crack growth rates are increased at the given applied cyclic stress intensity factor, ΔK. Equivalently, the observed threshold stress-intensity range ΔKth and the range of stress intensity factor ΔK for fatigue crack growth are decreased as the positive stress ratio is increased. Some fatigue steps and secondary cracks are observed on the fracture surfaces of the specimens tested at the three stress ratios. In addition, with the increase of the stress ratio, the toughness of the surface is increased and the secondary cracks are decreased. However, the fatigue fracture mechanisms of Ti-6.5Al-2Zr-1Mo-1V titanium alloy tested at the three stress ratios are all the same, which the fractures are all presented in transgranular mode.
2018, 38(3): 77-82. doi: 10.11868/j.issn.1005-5053.2017.000036
[Abstract](243) [FullText HTML] (97) [PDF 1450KB](17)
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Sandwich panels with multilayer pyramidal truss cores were manufactured by additive manufacturing. The compressive resistance and destructive behavior were obtained by test under compressive load. The experimental results show that the compressive behavior is very stable, and the load-displacement curves show the same change regulation. The node regions of pyramidal lattice emerge plastic deformation firstly with the increase of compressive load, and then several fractures occur at the node regions of the middle two layers. The average compressive strength of the sandwich panels with multilayer pyramidal truss cores is 6.72 MPa. The molding quality of the back of pyramidal truss is bad owing to the restriction of the technology, so the radius of the truss is smaller than theoretical value. The experimental compressive strength is smaller than theoretical value and simulation calculation value. The compressive strength by theoretical analysis is higher than experimental value because of idealized assumption; while the simulation calculation result agrees with experimental result, the error is around 20%. Comparing the load-displacement curves and deformation, the simulation calculation method will exactly calculate the compressive resistance and destructive behavior of sandwich panels with multilayer pyramidal truss cores.
2018, 38(3): 83-90. doi: 10.11868/j.issn.1005-5053.2017.000130
[Abstract](305) [FullText HTML] (114) [PDF 2270KB](17)
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The modified cyanate ester resin(CE) which can be applied stably in the cryogenic environment was prepared by using phenoxy resin(PKHH) and high purity epoxy resin(EP) through the method of melting prepolymerization. The results show that the curing reaction of CE is accelerated by the addition of PKHH, but the reaction pathways are not changed. It is found that PKHH can improve the ductility by the mechanism of the semi-interpenetrating network (SIPN) in the cured CE networks. Especially, the impact strength value of the CE/EP blends with the content of 10% (mass fraction) PKHH reaches to 18.4 kJ/m2 and the modulus is maintained at about 3.5 GPa at –196 ℃, accordingly the cracks are not observed on the surface of specimens after 20 low-high temperature cycles (–196 to 200 ℃).
2018, 38(3): 91-99. doi: 10.11868/j.issn.1005-5053.2017.000085
[Abstract](321) [FullText HTML] (126) [PDF 3547KB](11)
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To study the mechanical properties of composite solid propellant with initial interface defects, the mesoscopic structure model for HTPB (hydroxyl-terminated polybutadiene) propellant was established based on the periodicity assumption and molecular dynamics particle filled algorithm. The cohesive element method was employed for the adhesion interface between AP (ammonium perchlorate) particle and HTPB matrix, and the bilinear cohesive zone model was used to describe the mechanical response of the interface elements. Then, the space position and mechanical properties of the deficient interface were defined by the homemade program, and the macroscopic mechanical response of the propellant with interface defects was calculated based on the commercial finite element software ABAQUS. The stress-strain nephogram indicates that the interface with defects is earlier to debond and this also accelerates the process of the propellant fracture failure. The numerical simulation curves of the propellant with different contents of defects are compared. The result shows that the existence of interface defects reduces the mechanical properties of the propellant, and the higher defect contents obviously causes the lower mechanical properties. With the increase of the content of defects, the initial modulus and tensile strength of the propellant are decreased.
2018, 38(3): 100-106. doi: 10.11868/j.issn.1005-5053.2017.000041
[Abstract](241) [FullText HTML] (109) [PDF 2506KB](9)
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The tensile and compressive mechanical properties of laminates repaired by injection repair were experimentally studied, and the influences of repair on strength, stiffness and failure mode were evaluated. Control experiments between pristine, damaged and repaired specimens were designed, which including tensile and buckling unrestrained compression. The strain gauges were used to collect the deformation data in the test, and all the experimental data were analyzed and explained. The results demonstrate that strength of half-depth damage laminates is partially restored after repair. Strength recovery rate of tensile strength is 73.7% and that of buckling is 77.4%, and the weakest area is a filling area or the interface of panel and filler. Strength and stiffness of damaged specimens are reduced due to the coupling between extension/ compression and bending load as well as stress concentration, which are caused by the missing of material in damaged area. The stiffness of filler is smaller than that of motherboard, and the filler reduces the asymmetry of the damaged laminates and increases the stiffness of the repaired laminates.
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