航空材料学报

Effect of Minor Er and Y Additions to Al-Zn-Mg-Cu-Zr Alloy on Homogenizing Behavior

LI Guo-feng, ZHANG Xin-ming, ZHU Hang-fei

2010, 30(6): 1-6.

[Abstract](1522) [PDF 848KB](511)

Abstract:
Effect of minor Er and Y addition to Al-Zn-Mg-Cu-Zr alloy on the homogenizing behavior were studied by means of optical microscope(OM),different temperature analysis(DTA),scanning electron microscope(SEM),transmission electron microscope(TEM) and X-ray diffraction(XRD).The results indicate that when microalloying with minor Er and Y addition(gross 0.4%) to Al-Zn-Mg-Cu-Zr alloy,the dissolution temperature of the pseudo eutectic of the alloy rises,and the homogenizing temperature rises accordingly.After two-step homogenizing process,there is a few of the rudimental eutectic compounds for Al2CuMg and Al8Cu4Er phase in the alloy.The Al2CuMg phase dissolves after three-step homogenizing process,but the dissolution of the Al8Cu4Er phase is more difficult.After the three-step homogenizing process(annealing 465℃/24h + 475℃/4h + 485℃/4h),the rudimental eutectic compound is little,and a large number of the fine particles of the second phase are uniformly precipitated in the matrix,which is advantageous to restraining recrystallization of the alloy and raising the mechanical properties of the alloy.

Effect of Re Content on Microstructure and Mechanical Property of Directionally Solidified Superalloy

JIA Xin-yun, HUANG Zhao-hui, TAN Yong-ning, ZHANG Qiang, ZHANG Hong-wei

2010, 30(6): 7-10.

[Abstract](1472) [PDF 1175KB](273)

Abstract:
Effects of Re addition on microstructure and mechanical property of directionally solidified superalloys based on the compositions of DZ9 alloy were investigated.The results show Re addition enhances γ'-solvus temperature and incipient melting temperature.And Re content has effect on morphology of eutectic phase,size and morphology of γ'phase.With the increasing of Re content,the tensile strength increases gradually and the stress-rupture life improves remarkably.

Microstructure of Re and C-containing Ni-Based Single Crystal Superalloy

CAO La-mei, LI Xiang-hui, XUE Ming, ZHANG Yong, LI Ai-lan

2010, 30(6): 11-15.

[Abstract](1501) [PDF 969KB](303)

Abstract:
Microstructure of an as-cast and heat-treated Ni-based single crystal superalloy containing Re and C was investigated.The results show that γ' precipitates in dendrite core and interdendritic region have the same morphology with nearly cuboidal shape in the as-cast alloy.In the meantime,some eutectics and MC carbides exist in the interdendritic region.The eutectic was ruled out after solution heat treatment,as well as microsegregation was improved distinctly.The study of alloy after standard heat treatment showed that the γ' precipitates shape were regularly cuboidal shape,and the size and volume fraction were 0.32μm,61% and 0.41μm,68% in dendrite core and interdendritic region,respectively.The size and morphology of carbide have no change after heat treatment.TCP phases enriched in Re and W precipitated after 1095℃/100h in the dendrite core.

Microstructure and Deformation Behavior of TC21-0. 28%H Titanium Alloy

WANG Yao-qi, HOU Hong-liang, NIU Yong

2010, 30(6): 16-20.

[Abstract](1576) [PDF 743KB](309)

Abstract:
Microstructure of TC21-0.28% H titanium alloy was studied by optical microscope and X-ray diffractometry.High temperature deformation characteristics of TC21-0.28% H titanium alloy were investigated in the temperature range of 800 ～ 920℃ and the strain rate range of 0.01s ～ 1s-1 by thermo-simulation experiment.Constitutive equations were established.The results show that the β phase content of TC21-0.28% H alloy increases significantly comparing with TC21 titanium alloy.There are martensite α″ and δ titanium hydride precipitated in TC21-0.28% H titanium alloy.In α + β region and β region,deformation activation energy values is 233kJ/ mol and 153kJ/mol respectively and softening mechanism is dynamic recovery.Comparing with TC21 titanium alloy,deformation activa-tion energy of TC21-0.28% H alloy decreases,so hot-working character improves.

Effect of Water Spraying Parameters on Heat Transfer Coefficient of 7050 Aluminum Alloy during Quench

DENG Yun-lai, GUO Shi-gui, XIONG Chuang-xian, ZHANG Xin-ming

2010, 30(6): 21-26.

[Abstract](1565) [PDF 787KB](447)

Abstract:
End-quench test of 7050 aluminum alloy by spraying water with independent parameters of pressure(p) and average volumetric flux over spraying area(qs) was designed.Effect of parameters of p,qs and nozzle diameter(d) on heat transfer coefficient was studied.The results show that the maximum value of heat transfer coefficient(hmax) always occurs when the spraying surface tempera-ture is at 100～150℃,and the scale of hmax is 20000～50000W·m-2.℃-1.The 3-D diagram of hmax-qs-p was established,which reflects the effect of parameters of p and qs on heat transfer.The established 3-D diagram of hmax-k-qs,in which k represents ratio of spra-ying surface area to cross-section of nozzle,shows the effect of d on heat transfer.The diagrams of hmax-p-qs and hmax-k-qs are helpful to select quenching parameters(p,qs,k,et al) by spraying water.

New Aging Technique and Mechanism of High Strength,High Toughness and Low SCC Susceptibility in 7050 Aluminum Alloy

LI Jie, SONG Ren-guo, MA Xiao-chun, ZHENG Xiao-hua, LI Hong-xia, WENG Xiao-hong

2010, 30(6): 27-34.

[Abstract](1582) [PDF 1377KB](350)

Abstract:
7050 aluminum alloy was processed by single stage long term aging treatment.The microstructure and mechanical properties of different aging states were studied.The ability of stress corrosion resistance(SCR) in 7050 aluminum alloy was tested by DCB stress corrosion testing method.The results show that the strength of 7050 aluminum alloy after single stage long term aging treatment at different temperatures changes obviously.At first it gets the conventional peak value,then the strength decreases until to the lowest point,whereafter,the strength turns to increasing and gets the second peak value,the second peak value is higher than the first one.The fracture toughness increases with the aging extent increasing,the fracture toughness of the second peak is much higher than the first one.The stress corrosion cracking(SCC) susceptibility decreases when the aging extent increasing,the SCR property of the second peak is more excellent than the first one.After long time aging treatment on 135℃,the two strength peaks are obvious,the two peak value are much higher,the first strength value is σ0.2: 580MPa,σb: 625MPa,the second strength value is σ0.2: 590MPa,σb: 640MPa.The second peak'fracture toughness is much better,KIC = 39·5MPa.m1/2,the SCR is improved much,KISCC = 12.72MPa.m1/2.The observation of microstructure indicates that intracrystalline structure and the grain boundary structure are both very different between the two peak stages.The intracrystalline structure of the first peak is high density GP zone,the continuous banding η'phase distributes on the grain boundary.The intracrystalline structure of the second peak is mainly η' phase,the grain boundary structure is discrete thick η phase.

Influence of Shot Peening on High Temperature Fatigue Property of DZ4 Directionally Solidified Superalloy

GAO Yu-kui, JIANG Tao

2010, 30(6): 35-38.

[Abstract](1510) [PDF 999KB](229)

Abstract:
DZ4 directionally solidified superalloy was employed to investigate the effect of shot peening on surface integrity such as topography,surface roughness,microstructure,et al.by the methods of surface configuration tester,hardness tester and SEM.Fatigue properties of unpeened and shot-peened specimens of DZ4 superalloy were determined by rotating bending fatigue test at 820℃.The results show that shot peening improves the fatigue property of DZ4 directionally solidified superalloy,but the modification effect for notched specimens is greater than smooth ones.The comprehensive effect of shot peening including beneficial and detrimental factors was analyzed.

Ceramic Coating of WC-Co-NiCrAl/Laser-Remelting Microstructure and Corrosion Characteristics

HUA Guo-ran, GONG Xiao-yan, JU Zhi-lan, TIAN Zong-jun, ZHAO Jian-feng, HUANG Yin-hui

2010, 30(6): 39-42.

[Abstract](1473) [PDF 918KB](249)

Abstract:
Ceramic coating of WC/Co-NiCrAl(TC-1) coating was formed by plasma spraying technology on 1045 steel surface.Ceramic coating of WC-Co-NiCrAl/laser-remelting(TC-2) was formed by laser-remelting of the plasma spraying coating.Using nano-SiC powder material as the coating stuff,laser was also employed to remelt the plasma spraying coating,and the composite ceramic coating of WC/Co-NiCrAl/nano-SiC was formed(TC-3).The microstructures of three kind of composite ceramic coating were investigated using X-ray diffraction and scanning electron microscopy.Also,corrosion behavior of the coatings was studied.The results show that TC-1 ceramic coating consists of WC,W2C,W6C2.54,W,Co and CoO;TC-2 ceramic coatings are WC,W2C,CoC and W;TC-3 ceramic coatings are SiC,Si2W,WC,W and CoO.Lamella structure characteristic of plasma-sprayed coatings were eliminated after the laserremelting.TC-2 and TC-3 ceramic coatings have higher dense and better corrosion resistance than plasma sprayed TC-1 coating.

Dissolution Behavior of Corrosion Processing for TC1 and TC4 Titanium Alloy

LIN Cui, HU Ge, LIANG Jing, ZHAO Qing, DU Nan, WANG Li-qiang

2010, 30(6): 43-50.

[Abstract](1719) [PDF 1503KB](405)

Abstract:
E-t and polarization curves of corrosion processing for TC1 and TC4 titanium alloy were measured in hydrofluoric acid-nitric acid solution,and the rate variation of corrosion processing was discussed,meanwhile morphology of corrosion processing was observed.Active-passive transition characteristics were found in the polarization curve in hydrofluoric acid-nitric acid corrosion processing solution.In the case of hydrofluoric acid with high concentration,the polarization curve show the self-passivation trend when the concentration of nitric acid reaches the threshold value.The growth rate and the thickness of passive film were determined by volume ratio between hydrofluoric acid and nitric acid.In the condition of 1:2 volume ratio between hydrofluoric acid and nitric acid,corrosion processing rate was the greatest.At the initial period of corrosion processing,oxide film on the surface of titanium alloy was dissolved.Corrosion potential sharply became negative and faster corrosion processing rate was found.With the extension of time,nitric acid promotes the surface passivation,which results in the decrease of corrosion processing rate.The growth and destruction of passive film simultaneously occurred.Corrosion potential and corrosion processing rate tended to be stable when the growth of passive film and dissolution of the matrix achieved dynamic balance.Ti and Al of TC1 and TC4 titanium alloy were preferentially dissolved,and micro pits became shallow with the increasing concentration of nitric acid.

Near Net-shape Forming Technique with Mold Core of High Volume Fraction SiC_p/Al Composite in Pressureless Infiltration Process

CUI Yan, GUO Shun, ZHAO Hui-you

2010, 30(6): 51-56.

[Abstract](1302) [PDF 1059KB](258)

Abstract:
Near net-shape forming technique of high volume fraction SiCp/Al composites was realized by using aluminium-alloy-core with MgO coating in pressureless infiltration process.The microstructure,fracture surface morphology and phase constituent of SiCp/Al composite were analyzed by SEM,EDS and XRD.The results show that there was unobovious heterogeneous interface between SiCp/Al composite and aluminium-alloy-core,the SiC particles in composite near interface didn't collapse and distributed uniformly,the use of core didn't bring componential pollution to composite.The properties of composite near interface(about 500μm) and composite which is away from core including flexure strength,modulus of elasticity,density,coefficient of thermal expansion,thermal conductivity were tested,the results indicated the properties of composite near interface(about 500μm) and composite which is away from core didn't appear significant differences and the use of core didn't cause apparent degradation in property.The control on size was investigated and the result showed the high volume fraction SiCp/Al composite components with precise cavity was fabricated successfully by controlling reasonably the size of core in pressureless infiltration process.

Microstructure and Mechanical Properties of In-Situ Al₂O₃/TiAl Composites Doped with Fe₂O₃

XIANG Liu-yi, WANG Fen, ZHU Jian-feng, WANG Xiao-feng

2010, 30(6): 57-61.

[Abstract](1216) [PDF 1021KB](300)

Abstract:
Fe-doped Al2O3/TiAl composites were fabricated by in situ hot-pressing method with exothermic reaction of Al,Ti,TiO2 and Fe2O3 powder.The phase composition and microstructure of composites were characterized by XRD and SEM,the effects of Fe2O3 addition on microstructure and mechanical properties of the prepared composites were also investigated.The results indicate that the primary phases of composite are composed of TiAl,Ti3Al,Al2O3,and Al2O3 particles assemble on the boundary of matrix grains and the Al2O3-distribution regions connect each other.With the increasing of Fe2O3 content,the in situ Al2O3 particles are depressively distributed and the grains are refined,resulting in a better mechanical properties,the relative density and hardness of the composites are gradually increased.When the Fe2O3 content is 0.84%(mass fraction),there presents a better bending strength and fracture toughness,and the bending strength attains 624MPa,moreover,the fracture toughness reaches 6.63 MPa·m1/2.

Preparation and Characterization of Cycloaliphatic Polyester with Low Stress-Optical Coefficient and High Optical Properties

CHEN Yu-hong, LI Xi, YUAN Yuan

2010, 30(6): 62-67.

[Abstract](1526) [PDF 819KB](450)

Abstract:
Poly(1,4-cyclohexanedimethyl-1,4-cyclohexanedicarboxylate)(PCCD),a kind of cycloaliphatic polyester,was prepared by melt polycondensation of 1,4-cyclohexanedimethanol(CHDM) and 1,4-cyclohexanedicarboxylic acid(CHDA) in the presence of TBT as catalyst in a successive two-step polymerization.Esterification process and transesterification process were investigated including esterification temperature,transesterification temperature and reaction pressure at polymerization-under-vacuum stage.The optimal preparing conditions at various steps were then gained.FTIR and NMR were used to analyze the product and the result demonstrated the structure of PCCD.The optical tests show that PCCD is a kind of transparent polymer with high transmittance,low haze and yellow index,and low stress-optical coefficient.

High-Temperature Oxidation Resistance of MGH956 Alloy

LI Shuai-hua, TIAN Yun, LIU Guang-zu, YANG Zheng

2010, 30(6): 68-73.

[Abstract](1575) [PDF 1310KB](311)

Abstract:
The oxidation behavior of MGH956 alloy on 1000 ～1300℃ was studied.Analysis on morphology and composition of oxide scale was carried out by SEM and X-ray diffraction.Results show MGH956 alloy has very excellent oxidation resistance up to 1300℃ and internal oxidation is not found.α-Al2O3 is the main phase of the scale which is very adherent to substrate,as well as integrative and dense.And the grain size of oxide scale is fine,which enhances plasticity of the scale.All of those make the alloy possess very excellent oxidation resistance.

Effect of Crystal Structure of Co on Electromagnetic Properties of Co Coating Hollow Glass Microspheres

SU Yu-qin, ZHAO Yan, CHEN Ji-ping, ZHU Lei, ZHANG Zuo-guang

2010, 30(6): 74-79.

[Abstract](1723) [PDF 971KB](257)

Abstract:
Hollow glass microspheres coated with Co were obtained by electroless plating technique and they were treated by annealing method in vacuum condition.The hollow glass microspheres coated with Co were characterized by scanning electron microscopy(SEM),energy-dispersive spectrometry(EDS) and X-ray diffraction analysis(XRD).The microwave electromagnetic properties of hollow glass microspheres coated with Co(2.5g/cm3) were tested by network vector analysis.The magnetic properties were tested by vibrating sample magnetometer(VSM).The results show that annealing treatment induces the transformation of the crystalline phase which results in the improvement of the dialectical property.Annealing treatment also improves the soft magnetic properties of Co.

Damage Mechanism of Ductile Metals Based on Stress State Parameters

HE Min, LI Fu-guo

2010, 30(6): 80-86.

[Abstract](1444) [PDF 650KB](482)

Abstract:
Loading spectrum,integrating Von-Mises yield criterion with Tresca yield criterion,described the loading state in order to research the effects of loading mode on micro-crack initiation and growth at microscopic scale.A microcosmic view field model containing an elliptical inclusion was investigated in 5052 aluminum alloy and the inclusion was regarded as cohesive elements based on the loading spectrum.The stress state parameters were applied to explore the crack type and the initial location of crack under various load-ing modes.The results show that the microcrack firstly initiates at brittle phase,and the main reason is the inconsistent stress condition between matrix and inclusion.The overall scalar stiffness degradation(SDEG) predicts the crack nucleation location and the stress state parameters comprehensively describe the crack type.The same strain but the difference at crack nucleation shows that diaxial compression loading mode doesn't easily induce crack and pure shear loading mode is easier to initiate crack than the other loading modes.The analysis results agree with the experimental results.

Tensile Damage Behavior of 2D-C/SiC Composite

YANG Cheng-peng, JIAO Gui-qiong, WANG Bo

2010, 30(6): 87-92.

[Abstract](1520) [PDF 726KB](418)

Abstract:
The damage evolution and the tensile properties of 2D-C/SiC composite were investigated under monotonic and stepwise incremental loadings and unloadings.The experimental data show that the relational curves of the residual strain and unloading modulus versus the tensile stress have analogous form with the tensile stress-strain curve.Based on the micromechanics,a concise constitutive equation and a strength calculation model of the damaged material were established.The analysis reveals that the residual strain mainly depends on the crack opening displacement and the crack spacing,while the unloading modulus is significantly dependent on the interface debonding rate.Moreover,the uniaxial tensile behavior of 2D-C/SiC composite is mostly dominated by the longitudinal fiber bundles;the contributions of the transverse fiber bundles to the material's modulus and strength are obviously small.The predictions given by the presented model are in good agreement with the experimental data.

Comparison between 2-D Deterministic Model and Random Model of Voids in Composite Materials

ZHANG Xiang, LIN Li, CHEN Jun, GU Guang-ping, LI Xi-meng

2010, 30(6): 93-97.

[Abstract](1461) [PDF 826KB](377)

Abstract:
The principles and results were compared between the traditional 2-D deterministic model and random model of voids in the composite materials.The former assumed that all voids had regular shapes with the same size or fixed mathematical distributions distributed in isotropic homogeneous media.Based on the random medium theory,the latter investigated the random morphology of voids utilizing statistical method and characterized the elastic fluctuations from voids as small scale heterogeneities superimposed on the matrix,which is described by a spatial autocorrelation function with zero mean and some statistic parameters.It is found that,in terms of the random void model,not only good agreement of the geometry of voids between the modulations and microscopic images is observed,but also the predicted ultrasonic attenuation coefficient matches well the experimental results.It is concluded that the random void model is significantly superior to the traditional deterministic model for describing the morphology of voids in the composite materials.

2010 Vol. 30, No. 6