航空材料学报

Study of Effect of Mo on β Phase Stability and Theoretical Strength of Ti-Mo Binary Alloy by First-Principle

JIA Xiao, LI Jin-shan, TANG Bin, KOU Hong-chao, ZHOU Zhong-bo, CHANG Hui, ZHU Zhi-shou, ZHOU Lian

2010, 30(3): 1-4.

[Abstract](1520) [PDF 912KB](291)

Abstract:
Binding energy and electron structure of Ti-Mo binary alloys with different composition were calculated by Plane wave pseudopotential method and super-cell method on the base of density function theory,and unaxial theoretical tensile strengths of the alloys were obtained by binding energy curve of the deformed super-cell.Effects of the Mo content on the stability and strength of β-type Ti-Mo binary alloy together with their mechanisms were also studied.It is shown that the stability and strength of β-type Ti-Mo binary alloy increase with the increasing of Mo content;the analysis of density of states shows that the reinforcement of the bond between Ti and Mo make the theoretical strength of Ti-Mo binary alloys increase.

Homogenization of Al-Zn-Mg-Sc Alloy Ingot and Property Predicting Based on BP Neural Network

DENG Ying, YIN Zhi-min, HE Zhen-bo, SHI Kai

2010, 30(3): 5-9.

[Abstract](1403) [PDF 1517KB](221)

Abstract:
The microstructures and properties of Al-Zn-Mg-Sc alloy at different homogenization treatment condition were studied using hardness,electrical conductivity measurement and XRD analysis.The results show that the higher degree of super saturation in the as-cast alloy lead to the lower electrical conductivity and higher hardness.With the homogenization temperature increasing,the super saturation solid solution of as-cast alloy decomposed and T equilibrium phases precipitated at beginning,then dissolved back into the matrix,the degree of super saturation in the matrixes decreased firstly,and then increased,so the electrical conductivity increased firstly,and then decreased,the hardness decreased at the beginning,then increased.When the homogenization temperature increased further,the grain size grew up and the hardness of the alloy decreased again.Based on the research,BP neural network model was established,which could predict the properties of Al-Zn-Mg-Sc alloy ingot after homogenization treatment effectively.The model was designed by utilizing Matlab neural network toolbox and trained by Levenberg-Marquardt algorithm.The result shows that the BP model has high precision and good performance,the relative error of electrical conductivity within +0.23% and hardness within +1.90%.It can be successfully used to predict and analyze the influence of homogenization process on the properties of Al-Zn-Mg-Sc alloy ingot.Besides,it provided a feasible method for optimal design of the homogenization process.

Numerical Simulation of Solidification Process in Slab Casting Mould Based on 3D MiLE Algorithm Model

XUE Jian-guo, JIN Xue-wei, YAO Geng-yun

2010, 30(3): 10-13.

[Abstract](1457) [PDF 912KB](350)

Abstract:
According to the requirement of improving production efficiency and slab quality in a continuous steel slab caster,A 3D non-steady thermal-flow-stress model was developed to explore the solidification and flow process in mould.The width and thickness of slab are 1.2m and 0.2m,and respectively the steel grade is Q235B.The distributions of temperature,flow,stress and strain in caster were obtained by using the commercial software,ProCAST.The results show that the shrinkage of slab has different shape curve on different direction.Consider of the effect of gap width,the average temperature at mold exit increases form 1120.5℃ to 1289.7℃,and the shell thickness decreases from 16.1mm to 14.2mm.

Ultra-Fine-Grained Copper with High Strength and Conductivity Fabricated by Severe Deformation of Asymmetrical Accumulative Roll Bonding

WANG Jun-li, SHI Qing-nan, QIAN Tian-cai, WANG Shao-hua, YANG Xi-kun

2010, 30(3): 14-18.

[Abstract](1471) [PDF 668KB](351)

Abstract:
Ultra-fine-grained copper was prepared by asymmetrical accumulative rolling bonding(AARB) with annealing.The main characteristics of AARB technology were discussed,including rubbed rolling area,interface and deformation rate,the structures and properties were measured.The results show that the rubbed rolling area promotes the interface recombination and grains refinement.There are much sub-structures within oxygen-free copper after AARB for six passes with 4.01 cumulative true,thereafter,when annealed by 220℃/35min,the sub-structures disappear and the ultra-fine-grained copper with high strength and conductivity has been obtained,which grain size is 200nm,tensile strength and yield strength are 424.5MPa and 323.1 MPa respectively and electrical conductivity is 76.3MS/m.The increase of grain boundary area of ultra-fine-grained copper increases the microhardness.Small uneven deformation and stress concentration for ultra-fine grained copper lead to a better good plastic and higher intensity.The plastic deformation mechanism of ultra-fine-grained copper is controlled by grain boundary.

Phase and Microstructure of TC21 Titanium Alloy During Slow Cooling

DANG Wei, XUE Xiang-yi, KOU Hong-chao, CHANG Hui, LI Jin-shan, ZHANG Feng-shou, ZHOU Lian

2010, 30(3): 19-23.

[Abstract](1647) [PDF 2451KB](290)

Abstract:
The phase and microstructure of TC21 titanium alloy during cooling from β phase field at differently slow rates were studied by OM,XRD and SEM.The results show that the main phase transformation was β→α during cooling,and the precipation of Ti2AlNb(O)and Ti2AlNb(B2)phases were discovered.When cooling rate was 1℃/min,α precipitates nucleated at the grain boundary,then growed towards transgranular,and finally forms fully lamellar microstructure.Whereas,nucleation of α precipitates during cooling with 5℃/min taked place at grain boundaries and was also accompanied by appearing at intragranular sites,which resulted in final microstructure was lamellar microstructure with a little basketweave microstructure.The effect of cooling rate on microstructure received at room-temperature was visible.Thickness of α laths,α colonies size and fraction of α laths all decreased with the cooling rates reducing.

Effect of Re on Microstructure and Properties of Directionally Solidified Superalloy

ZHANG Jun, ZHANG Ai-bin, TAN Yong-ning, JIA Xin-yun

2010, 30(3): 24-27.

[Abstract](1449) [PDF 1593KB](265)

Abstract:
The effect of different content of Re in alloys on microstructure and the mechanical properties were investigated.The results show that Re distirbutes mainly in γ matrix,the amount of the γ+γ′ eutectic phases of increases due to Re addition and the size of γ′ phase particles in the dendrite core decreases mankedly.After heat treatment,the shape of γ′ phase particles tends to be more cubic,the amount of the γ+γ′ eutectic phases decreases obviously.The tensile yield strength at room temperature and stress rupture life at 1100℃/70MPa increase obviously with increment of Re content,while the elongation decreases.

Synthesis of Ternary Machinable Al₂O₃/Ti₃AlC₂ Ceramic by High Energy Milling and Hot-Pressing

LIU Bo-bo, WANG Fen, ZHU Jian-feng, LI Ya-ling, CUI Xiang-yang

2010, 30(3): 28-31.

[Abstract](1476) [PDF 865KB](187)

Abstract:
Al2O3/Ti3AlC2 composites was synthesized by high energy milling and hot-pressing using Ti,Al and C powders as raw materials.That is in the process of synthesis Ti3AlC2 layered material the composites were synthesized.The effects of sinering temperature on reactions,the microstructure and reaction of mechanism were investigated based on the analysis of XRD,EDS and SEM.The results show that Al2O3/Ti3AlC2composites was successfully obtained by hot-pressed at 1200 oC.The synthesizing temperature was decreased by high energy milling.Meanwhile,the microstructure show that Al2O3 evenly distributed in Ti3AlC2 substrate,forming dense layer of oxide film on the surface,and hindering the expansion of surface micro-cracks in the fracture process.Moreover,the mechanical properties of the composites were enhanced due to the effect of micro-crack toughening.

Effects of Hot Compression on Microstructure of SiC_p/Al Composite with High Volume Fraction

ZENG Li, WANG Xiao-li, CUI Yan, REN Xue-ping

2010, 30(3): 32-37.

[Abstract](1440) [PDF 2216KB](187)

Abstract:
Structural-Functional SiCp/Al Composite with high volume fraction(～55%) was prepared by pressureless infiltration.Hot(above melting point of matrix) compression on the composite was tested.Effects of hot compression parameters on phase composition and Microstructure of SiCp/Al composite with high volume fraction were observed and analyzed by using XRD and SEM.The results show that phases such as Al,SiC,a few Si and Mg2Si still exist in SiCp/Al Composite with high volume fraction by Hot Compression,High temperature stability of the composite is good;When SiCp/Al composite with high volume fraction is compressed at high temperature,matrix remains contiguous,particle would roll over by pressure,some particles break,microstructure features such as size and distribution uniformity are controlled by hot compression parameters.The size,roundness and distribution uniformity of SiC particle increase with increasing deformation temperature and decreasing strain rate;SiCp/Al Composite with high volume fraction can be concerned as Viscous fluid above melting point of matrix,it can be considered fluidity.Effects of deformation temperature and strain rate on composite’s fluidity make microstructure features of composite by hot compression show four steps.

Fabrication and Properties of Hollow Silica Fiber Reinforced Nitride Composites of Low Dielectric

ZOU Xiao-rong, ZHANG Chang-rui, WANG Si-qing, CAO Feng, LI Bin, SONG Yang-xi

2010, 30(3): 38-42.

[Abstract](1489) [PDF 668KB](353)

Abstract:
Hollow silica fiber reinforced BN-Si3N4 matrix composites were fabricated by repeated infiltration and pyrolysis using a hybrid precursor containing borazine and perhydropolysilazane,and the effects of temperature on the densification behavior,mechanical properties,dielectric properties and microstructures of the composites were investigated.The results show that with the increase of the pyrolysis temperature from 300℃ to 500℃,the density of the composites increases,the elastic modulus increases accordingly,but the flexural strength shows a maximum value followed by an obvious decrease.The composite prepared at 400℃ exhibits a maximum flexural strength of 132.4MPa,which results from the good state of the silica fibers and controlled fiber/matrix interfacial microstructures.The dielectric constant also increases with the increase of temperature,but the dielectric properties of the composites prepared at three different temperatures are all good,with low dielectric constants of 2.60～3.01,and low loss angle tangent values below 5×10-3,which results from the high purity hollow silica fiber of the excellent dielectric properties and low density non-carbon nitride matrix.

Characterization of Surface Properties of Carbon Fibers and Interfacial Properties of Carbon Fibers Reinforced Matrix Composites

SHI Feng-hui, DAI Zhi-shuang, ZHANG Bao-yan

2010, 30(3): 43-47.

[Abstract](1540) [PDF 1694KB](609)

Abstract:
The surface physical and chemical properties of T300-3K and T300-6K carbon fibers were characterized and the interfacial properties of these carbon fiber reinforced epoxy composites were also studied.Results indicated that the O/C ratio and acitve carbon ratio of T300-6K carbon fiber were higher than that of T300-3K carbon fiber.T300-3K fiber had the rougher surface while it grooves were lower,narrower and shorter than that of T300-6K carbon fiber.The interfacial shear strength(IFSS) of T300-3K and T300-6K carbon fiber reinforced epoxy composites were in the same range.

Residual Stresses of Injection Molded and Injection Compression Molded Auto Glazing

CHEN Yu-hong, YUAN Yuan, LI Xi ZHAN Mao-sheng

2010, 30(3): 48-54.

[Abstract](1497) [PDF 2357KB](257)

Abstract:
Numerical models of residual stresses were established based on a series of governing equations for injection molding and injection compression molding.Then the models were applied in analyzing residual stresses of injection molded and injection compression molded auto glazing.The results show that residual stresses of injection-compression molded glazing are much smaller and evener than those of injection compression molded parts,and this is associated with low flow resistance of polymer melt,uniform distribution of in-mold stress and bulk temperature in the process of injection compression molding.Polycarbonate glazing were molded,and the polarized light test results also verified the numerical simulations.

Effect of Water Blowing Agent on Structures and Properties of Polyimide Foams

ZHAN Mao-sheng, XU Xiao-qiang, PAN Ling-ying

2010, 30(3): 55-60.

[Abstract](1543) [PDF 1992KB](447)

Abstract:
Polyimide foams were prepared by single-stage process condensation,and study the effect of water content on their structures and properties.The molecular structure and cell structure of polyimide foams were characterized by FTIR and SEM,respectively;the glass transition temperature and thermal stability of polyimide foams were characterized by TMA and TGA,respectively;sound absorption properties of polyimide foams was characterized by two channels acoustic analyzer.The results show that the water content has no effects on the molecular structure,the glass transition temperature and thermal gravimetric properties of polyimide foams in the study range of water content;the biggest average absorption coefficient of polyimide foams measured by using standing wave pipe method is 0.44;the glass transition temperature of polyimide foams is between 294.7℃and 295.6℃,and the temperatures at 5% weight loss is higher than 377.5℃,the residual weight ratio at 800℃ is higher than 49.6%.

Theoretical and Experimental Evaluation of Thermal Conductivity of Polyimide/Silica Composite Films

CAI An, YANG Li-ping, Luo Cai-yun, CHEN Jiang-ping, XI Tong-geng

2010, 30(3): 61-65.

[Abstract](1644) [PDF 544KB](324)

Abstract:
Different models for thermal conductivity prediction of composite materials were evaluated and analyzed with experimental values.Laser flash method and differential scanning calorimeter were employed to carry out the measurements of thermal diffusivity and specific heat of polyimide/silica composite films with different silica contents.The thermal conductivity was calculated and compared with prediction and the results show that the Sorin model considering filler size distribution fits better with experimental data.Both prediction and experimental values indicate that thermal conductivity of polyimide/silica composites increases with the increase of silica content,and increases with temperature rise in temperature range 20～160℃.

Preparation and Properties of Octadecane-Palmitic Acid/Expanded Graphite Phase Change Energy Storage Materials

MA Feng, LI Yan, CHENG Li-yuan, CHEN Ming-hui

2010, 30(3): 66-69.

[Abstract](1450) [PDF 823KB](362)

Abstract:
Octadecane-palmitic acid/expanded graphite phase change energy storage materials were prepared by vacuum infiltration method using the eutectic mixture of octadecane(OC) and palmitic acid(PA) as phase change materials,expanded graphite(EP) as skeleton.In such a composite,expanded graphite has porous structure,which prevents leakage of the melted phase change materials because of the effect of capillary force and surface tension force.The structure and properties of the materials were analysised by SEM,DSC and the test of melting and solidification process.The results show that phase change materials are well sealed into the inner pore of porous graphite,and the composite with expanded graphite skeleton has high thermal conductivity,high latent heat and steady thermal performce,so it can be used in thermal energy storage and heat recovery system.

Study of Hill′s Yield Criterion Application for DD3 Single Crystal

ZHAO Ping, HE Qing-hua, LI Wei, LU Bo, DING Zhi-ping

2010, 30(3): 70-73.

[Abstract](1540) [PDF 1146KB](241)

Abstract:
Hill’s yield criterion for plastically orthotropic solids is used to predict the yield stress of single crystal alloys DD3 at different temperature along different orientations.Results showed that the prediction precision was greatly affected by the choice of material parameters in Hill criteria and the yield stress of single crystal along three primary loading orientations couldn’t be predicted accurately at the same time.Taking into account the effects that the components of tension and torsion stresses are coupled with each other,a new yield criterion for single crystal nickel-based superalloys is put forward in term of the characteristics of single crystal nickel-based superalloys by introducing a modified item into Hill ’s yield criterion.Using the new yield criterion to predict the yield stresses of single crystal alloys,the correlation along [001], [011] and [111] orientations to experiments is very good and more accurate than that of Hill’s,other orientations is satisfied also.

Test Research on Fatigue Crack Propagation Law in Aluminum Alloy 7B04-T6 under Flight-by-Flight Spectrum

LIANG Chao, HE Xiao-fan

2010, 30(3): 74-77.

[Abstract](1584) [PDF 556KB](235)

Abstract:
In order to educe the fatigue crack propagation law under flight-by-flight spectrum,several experiments on CCT specimen made from aluminum alloy 7B04-T6 were tested under constant amplitude spectrum of two kinds of stress ratio and three kinds of flight-by-flight spectrum.The study educes parameters in Paris equation of stable crack growth range under constant amplitude spectrum.According to Paris equation the study educes fitting parameters of stable crack growth range under flight-by-flight spectrum in which the unit is block.The results indicate that the constant n in Paris equation under flight-by-flight spectrum is related to spectral intensity obviously which can reflects the spectral intensity of flight-by-flight spectrum.

Analysis of Test Factors Affecting Laminar Shearing Strength of Stretched Acrylic

CHEN Jie

2010, 30(3): 78-81.

[Abstract](1433) [PDF 830KB](313)

Abstract:
The effect of the test speed,the sample thickness and the sampling direction on the laminar shearing strength of the stretched acrylic were investigated.The result shows that,the higher the test speed,the greater the shear strength.At the speed of 1～5mm/min,the sample can be pure laminar sheared with a smooth testing process.The thinner sample can be sheared successfully.When the thickness is above 10mm,the sample must be milled to 10mm from one side.For two axis stretched acrylic,the sampling direction has no effect on the laminar shearing strength of the stretched acrylic.

Study on Influence Factors of Small Punch Test Based on Ductile Damage Numerical Analysis

ZHOU Zhi-xiang, LING Xiang

2010, 30(3): 82-87.

[Abstract](1474) [PDF 2115KB](268)

Abstract:
A finite element model(FEM) for small punch test(SPT) specimen damage numerical analysis was established based on Gurson-Tvergaard-Needleman(GTN) ductile damage constitutive equations.SPT for SUS304 was performed at room temperature on round specimens with dimension of.The validity of FEM was proved by load-displacement(L-D) curves and rupture location from experiment and simulation.Effects of friction coefficient,sample thickness,steel ball diameter,center hole diameter of the lower die and punching velocity on SPT results were analyzed by finite element analysis(FEA).The results show that the five factors mentioned above have significant influences on L-D curve,ultimate load,rupture time,initial crack and necking location of SPT specimen.Meanwhile,the current deficiency of simulation for SPT was pointed out and overcomed,the acquired conclusions guide the future healthy development of SPT technique.

Aircraft Design Material-Selection Method Based on MAUT Theory

LAN Yuan-pei, MENG Qing-chun, LI Feng, XU Guang-xing, GUAN Zhi-dong

2010, 30(3): 88-94.

[Abstract](1595) [PDF 317KB](503)

Abstract:
Multiple attribute decision making(MADM) theory and its application in engineering materials selection are introduced,with basic application processes summarized.Then to serve the materials selection in metal airframe design,an aircraft-design material-selection method based on multi-attribute utility(MAUT) theory is proposed.A material-performance evaluation-index system for primary structures material selection is proposed so as to meet material performance requirements under different airframe design principles,and key points in using MAUT-based material selection methods are also put forward.Its effectiveness is demonstrated by the wing-spar material-selection case of a fighter.

2010 Vol. 30, No. 3