航空材料学报

First-Principles Study on Elastic Properties of B₂-NiAl Intermetallic Compound with Ag Addition

CHEN L?, WEN Tao

2011, 31(2): 1-7.

[Abstract](1586) [PDF 1014KB](503)

Abstract:
Using the first-principles pseudopotential plane-wave methods based on the density functional theory,the elastic constants of B2-(Ni1-xAgx)Al(x=0~1%,atom fraction,) supercells with or without Ni vacancy or Ni anti-site defect were calculated in the framework of Virtual Crystal Approximation.Several parameters such as elastic constant C44,Cauchy pressure(C12-C44),Elastic modulus E,the shear modulus G and their ratio G/B0 were adopted to characterize and assess the effect of Ag alloying concentration on the ductility and hardness of NiAl intermetallic compounds.Ag addition with x1% is proved to be efficient to enforce the strength or hardness of NiAl intermetallic compounds either for perfect crystals or for defect crystals.Adding Ag in the range of 0 to 0.6% and 0.7% to 1%,especially about 0.6%,help to improve the ductility of perfect B2-NiAl.Ni vacancy or Ni anti-site defects make the intrinsic ductility of perfect B2-NiAl crystals without Ag addition to be weakened.Moreover,the ductility of B2-(Ni1-xAgx) Al crystals with Ni vacancies or Ni anti-site is obviously improved as Ag alloying concentration x is lower than 0.5%(0.32% to 0.48%,especially) or is in the range of 0.5% to 1%(0.73% to 1%,especially) respectively.The alloying effect attribute to solid solution hardening of Ag atom in low concentration and inteneration of Ag-rich phase in high concentration.

Static Recrystallization Kinetics of Haynes230 Superalloy

PENG Cong-Hui, CHANG Hui, HU Rui, FAN Jiang-kun, BO Guang-hai, FU Heng-zhi

2011, 31(2): 8-12.

[Abstract](1654) [PDF 963KB](269)

Abstract:
The static recrystallization behavior and kinetics of Haynes230 superalloy were investigated.The results show that homogeneous and fine grains of the alloy are obtained through annealing at 1100～1150℃ after cold rolling.The relationship between volume fraction of the recrystallization grains and annealing time can be described by the JMAK equation.Based on the experimental data,the calculated activation energy decreases range from 402kJ/mol to 318kJ/mol with the cold deformation increasing.As the temperature rose,the time for recrystallization completion shortened with range of 74.51～5.43min.The temperature had significant influence on the velocity of recrystallization.At the meantime,the recrystallization kinetics curve of Haynes230 superalloy was worked out,which is a theoretical guidance for the microstructural refinement.

Effects of Homogenization Treatment on Microstructure and Properties of 7A55 Aluminum Alloy

LI Zhong-sheng, PAN Fu-sheng, WU Hu-lin, CHEN Yun-ru

2011, 31(2): 13-17.

[Abstract](1337) [PDF 1185KB](295)

Abstract:
The effect of single homogenization treatment and two-stage homogenization treatment on microstructure and properties of the as-cast 7A55 aluminum alloy were investigated.The results show that the residual eutectic structure is still more after single homogenization treatment at 450℃.After 450℃/60h homogenization treatment,the area fraction of residual eutectic decreases from 15.2% to 7.2%,and hardness reduces from 72HRB to 60HRB,whereas elongation increases from 2.1% to 11.2%.The non-equilibrium eutectic significantly reduces after 450℃/60h+470℃ two-stage homogenization.It is found that a large number of equilibrium phase is precipitated during cooling.After 450℃/60h+470℃/12h two-stage homogenization,the area fraction of residual eutectic is only 2.3%,and hardness is reduced by about 17HRB compared to the as-cast alloy.In the meanwhile,the elongation is 15.3%.According to the experimental results,the proper homogenization treatment of 7A55 aluminum alloy is 450℃/60h +470℃/12h.

Research on Quench Sensitivity of B93 Aluminum Alloy for Large Sized Bars

JIAN Hai-gen, JIANG Feng, LI Jin-long, ZHENG Xiu-yuan, WEI Li-li

2011, 31(2): 18-23.

[Abstract](1275) [PDF 1282KB](230)

Abstract:
The quench sensitivity of the Al-Zn-Mg-Cu alloy for large sized bars were studied by means of hardness test,X-ray diffraction analysis,finite element simulation and microstructure observation.The results show that,the closer to the centre of the quenching bars,the larger quantities of equilibrium MgZn2 are observed in the grain inner and on the grain boundary and keep growing up.And small quantity of hardening precipitates are exhibited in the 120℃/24h aging samples.It results in the decline of the age-hardening effect.For the surface of the bar,the second phase was not observed and the homogeneous content in the grain inner was obtained,which may attribute to the super saturated solid solution.A number of η′dispersoid were found at the surface.The dispersive phases are able to promote the precipitation strengthening effect and the hardness of the alloy reach the peak.The value of the quenching depth is 30mm,and the critical quench cooling rate is 15℃/s.

3D Finite Element Simulation and Experimental Test on Residual Stress Field by Hole Cold Expansion

LIU Xiao-long, GAO Yu-kui, LIU Yun-tao, CHEN Dong-feng

2011, 31(2): 24-27.

[Abstract](1345) [PDF 1070KB](299)

Abstract:
The residual stress field of 7050-T7451 aluminum alloy with different thickness caused by hole cold expansion was simulated by FEM using ANSYS codes.The results show that the residual compressive stress of the hole edge exists grades across the thickness and the residual compressive value is smallest at the entrance,so the entrance becomes the most weakest region.With the increment of the thickness,the residual compressive stress at the entrance increases until reaching the maximum,then decreases and gradually tends to a stable value.The residual stress of the specimen was measured by the X-ray.The results show that residual stresses are obviously less compressive on the entry surface compared to the exit surface.The measurement was consistent with the FEM simulation.

Influence of Ultrasonic Impact Treatment on Fatigue Properties of 2A12 Aluminum Alloy Welded Joints

LI Zhan-ming, ZHU You-li, XIN Yi

2011, 31(2): 28-32.

[Abstract](1372) [PDF 1233KB](354)

Abstract:
2A12 aluminum alloy welded joint was full coverage strengthened by ultrasonic impact treatment(UIT).The S-N curves of welded joint samples with and without UIT were set up by making bending fatigue test.The effect of UIT on fatigue properties of aluminum alloy welded joint was analyzed.The fatigue fracture mechanisms of these samples with and without UIT were studied by microstructure,residual stress and fracture surface analysis.The results showed that the fatigue limit of 2A12 aluminum alloy butt-welded joints was increased 38.5%.At the same time,the surface defects of welded joints were reduced substantially after ultrasonic impact treatment.The coarse-grained microstructures of top-surface layer of welded joint were refined after the UIT.The metallurgical structure of the near surface material of the joint was thus density.Compressive residual stress was induced at the surface of welded joints by UIT.

Study of Deposition Process and Properties of PbSe Films Grown by Chemical Liquid Deposition

LUO Fei, WANG Jin-peng, TAO Chun-hu, LI Zhi, LIU Da-bo

2011, 31(2): 33-36.

[Abstract](1311) [PDF 1130KB](246)

Abstract:
Chemical liquid deposition of PbSe semiconductor thin films in solutions of lead acetate were carried out.The effects of deposition time on the crystal structure,morphology and optical properties were investigated by XRD,SEM and Optical Transmittance Spectra.It revealed that highly crystallized PbSe films grew at different deposition time with cube structure.With increasing of deposition time,films turn compact and Pb/Se atom ration increased.All the films were Se rich in the surface.The thickness of the films had an effect on their optical properties,the absorbance grew up with the thickness increase.

Investigation of Curing Characterization of Acetylene-Terminated Polyisoimide Oligomer

LI Bin-tai, XING Li-ying, ZHAO Tong, LIU Feng, CHEN Xiang-bao

2011, 31(2): 37-42.

[Abstract](1306) [PDF 1433KB](290)

Abstract:
The curing of acetylene-terminated polyisoimide oligomer was investigated using DSC and FTIR spectroscopy.Through dynamic and isothermal FTIR method,the isoimide-imide isomerization and crosslinking reactions of the oligomer was monitored individually and the temperature ranges of these two reactions were clearly determined.The fact that the isomerization occurred at a lower temperature ranges than the crosslinking is attributed to the difference between the activation energies of the two reactions,79.635kJ/mol for isomerization and 106.469kJ/mol for crosslinking.For the acetylene-terminated polyisoimide oligomer considered here,curing reaction was achieved to a sufficient extent at the temperature range of 200~220℃.Posture temperature is in the range of 300~350℃.

Study on Interface Compatibility of T700S/QY8911 Composite

PENG Gong-qiu, YANG Jin-jun, CAO Zheng-hua, XIE Fu-yuan

2011, 31(2): 43-48.

[Abstract](1561) [PDF 1344KB](255)

Abstract:
T700S/QY8911 composite was prepared by hot melt mixing prepreg using autoclave processing.The viscosity-temperature property of QY8911 was studied,and then the interface compatibility of T700S and QY8911 composite was synthetically investigated by surface tension and contact angle measurement,interfacial shear stress test,glass transition temperature(Tg) determination before and after moisture absorption,basic mechanical properties tests and fracture morphology analysis.Results show that QY8911 bismaleimide possessed longer temperature and time range at low viscosity,excellent technological applicability of T700S/QY8911 prepreg,and the optimal temperature for making prepreg is 90～110℃.The interfacial shear stress of T700S/QY8911 composite has good retention ratio at high temperature,and its Tg descend only 19℃ after 360 hours′ immersion.In addition,the retention ratio of basic mechanical properties was above 50% under high temperature and humidity,and close connection between the fibers and resin was observed from fracture morphology of interlaminar shear samples.Therefore,all the results indicate that the T700S/QY8911 composite has good interface compatibility.

MicroCT Characterization on Microstructure of C/SiC Composites

FENG Yan-jian, FENG Zu-de, LI Si-wei, ZHANG Wei-hua, LUAN Xin-gang, LIU Yong-sheng, CHENG Lai-fei

2011, 31(2): 49-54.

[Abstract](1565) [PDF 1469KB](312)

Abstract:
Nondestructive three-dimensional structure of 3D C/SiC composites fabricated by chemical vapor infiltration(CVI) was characterized using X-ray microcomputed tomography(MicroCT).The current study was undertaken to assess the capabilities and limitations of MicroCT for the characterization of C/SiC composites.Results demonstrate that MicroCT can facilitate characterization of fabric morphology,defects(porosity and the different densities of SiC matrix) in 3D C/SiC composites.A gas retention and viscous flow formation in the preform was revealed in the light of three-dimensional porosity.A nodular surface morphology of SiC matrix fabricated by CVI was observed by reconstructing the matrix porosity-wall.Comparing with the SEM surface morphology of SiC coating fabricated by chemical vapor deposition(CVD),pressure difference between the inner and outer preform was demonstrated.

Comparison on Optical Properties of Injection Molded and Injection Compression Molded Transparencies

CHEN Yu-hong, YUAN Yuan, LIU Xiao-yan, GUO Dan-dan, BAI Yi-feng

2011, 31(2): 55-60.

[Abstract](1307) [PDF 1411KB](288)

Abstract:
Optical properties,residual stress and thickness distribution of injection molded(IM) and injection compression molded(ICM) transparencies were tested and molding principles of the transparencies were also studied.The results showed that ICM transparencies had similar appearance quality,transmittance and haze to IM parts,as a result of the same material and close surface roughness.But ICM parts possessed much smaller birefringence,optical distortion and angular deviation than IM parts.ICM parts exhibited little molecular orientation,thus having well-distributed residual stresses and low birefringence.Low optical distortion and angular deviation of ICM parts were not only associated with small and well-distributed residual stresses,but also related to even shrinkage.Consequently,optical quality of ICM transparencies was superior to that of IM transparencies.

Effects of Honeycomb Cell Size on Performances of Sandwich Panels

SUN Shi-ping, LAI Yu-dong

2011, 31(2): 61-66.

[Abstract](1344) [PDF 1433KB](227)

Abstract:
Honeycomb sandwich panel was studied to reveal the effects of the cell size in the static analysis and the free vibration analysis.The response of the sandwich panel with the homogenized cores was used as the standard of comparison.The ratio of the responses of the detailed finite element models of sandwich panels to the corresponding comparison solutions was defined as a Size Influencing Index that reflects the influences of the size variation of different cell configuration.Based finite element technique,the static and the free variation response of honeycomb sandwich panels with the different cores and the homogenized cores were analyzed comparatively,under three typical boundary conditions,including the hexagonal,triangular and square honeycomb core.The computed results reveal the size effect of the honeycomb cell on the stiffness and the frequency behavior of sandwich panel.It is shown that when the ratio of the macrostructure size to the cell size is larger than 12,the influence of the cell size on the sandwich panel performances tends to gentle weakening.Meanwhile,when the cell size and macrostructure size are comparable with each other,the size effect is quite obvious,and the degree of influence is significantly dependent on the boundary condition and the cell configuration.

Effect of Yttrium Aluminum Garnet on High-Temperature Properties of Alumina-Based Ceramic Cores

XU Dong-yang, LI Di-chen, WU Hai-hua, XING Jian-dong, SUN Bo

2011, 31(2): 67-71.

[Abstract](1424) [PDF 1491KB](317)

Abstract:
A new strengthening process was developed to improve the high-temperature properties of alumina-based ceramic cores by vacuum pressure impregnation(VPI) with yttrium sol as reinforcing agent.The experimental results showed that the high-temperature properties of the cores were improved significantly as impregnating times increasing.After three times impregnation strengthening,the deformation at 1550℃/0.5h decreased from 7.38 mm to 0.72 mm and the flexural strength at 1550℃ increased from 0.95MPa to 4.61MPa.Meanwhile the apparent porosity still kept above 40% to guarantee the core leach property.X-ray diffraction revealed that the content of YAG(yttrium aluminum garnet,a high-temperature strengthening phase)was increased through VPI,which was obviously observed by SEM.

Oxidation Resistance at High Temperature of Fe₃Si Intermetallic

ZHOU Qi, JIA Jian-gang, ZHAO Hong-shun, LIU Jian-jun, WU Hai-tao

2011, 31(2): 72-78.

[Abstract](1438) [PDF 1586KB](232)

Abstract:
Fe3Si intermetallic was prepared using vacuum arc melting.The oxidation products of Fe3Si intermetallic were characterized by XRD,SEM,EPMA.Meanwhile,Fe3Si oxidation resistances were studied at temperature 800℃ and 900℃.The results show that the oxidation resistance of Fe3Si intermetallic is better than AISI 304 stainless steel at temperature 800℃ and 900℃.The oxidizing dynamics curves of Fe3Si was complex curves conforming to parabolic rule and linear rule at temperature 800℃.But at temperature 900℃ it was single parabolic curves.The initial growth mechanism of oxide layer was diffusion process of Si at temperature 800℃,and then with the crumbling of oxide layer,the growth mechanism was diffusion process of Si.The process of the oxidation kinetics was controlled by diffusion process at 900℃.Diffusion process of Si played a leading role in growth mechanism of oxide layer,with a mass transfer of Fe moved away from SiO2 of film.

Investigation on Curing Kinetics and Dielectric Properties of Nano-TiO₂/BMI/CE Composites

WU Guang-lei, KOU Kai-chang, CHAO Min, JIANG Yang, ZHANG Dong-na, ZHANG jiao-qiang

2011, 31(2): 79-84.

[Abstract](1345) [PDF 1483KB](253)

Abstract:
The non-isothermal curing kinetics of nano-TiO2/BMI/CE copolymers were studied by using the differential scanning calorimetry(DSC).The curing kinetics parameters of the modified system were obtained by Kissinger equation,Ozawa equation and Crane′s theory.The effects of different curing processes and post-process temperatures on the dielectric performances of nano-TiO2/BMI/CE system were investigated.The results show that better dielectric properties of microwave curing system are also compared with these of conventional heat curing system under the same content of nano-TiO2/BMI/CE.Dielectric properties of microwave curing nano-TiO2/BMI/CE composites get more increasing via controlling post-process temperatures and post-process time.

Approach Study of Improving Surface Corrosion Resistance of 6063 Aluminum Alloy

ZHANG Jian-xin, GAO Ai-hua

2011, 31(2): 85-88.

[Abstract](1246) [PDF 1310KB](260)

Abstract:
The approach to improving surface corrosion resistance of 6063 aluminum alloy was studied,and the mechanism of surface corrosion resistance was discussed in theory.The results indicate that reasonable chemical composition is of advantage to corrosion resistance,its property is better as Mg,Si mass ratio at about 1.55.The necessary homogenizing treatment of cast ingot subserves corrosion resistance of aluminum extrusion,and the cast ingot should be cooled quickly after heat treatment.Significant effect of extrusion technology on erosive property is observed for aluminum alloy,aluminum extrusion has good corrosion resistance when outlet temperature is at about 510℃.

Hot Cracking Behavior of A206/1%Al₂O₃ Aluminum Base Nanocomposite

LI Ke, WANG Qian, ZHOU Nai-geng, GAO Ting

2011, 31(2): 89-94.

[Abstract](1472) [PDF 1520KB](220)

Abstract:
A206 aluminum alloy is rarely used in critical applications because of its high propensity for hot cracking.A206/1% Al2O3 nanocomposite was prepared with ultrasonic dispersion method.The hot cracking susceptibility(HCS) was evaluated using constrained rod casting in a steel mold.And microstructure of the alloys was analyzed by Optical Microscopy(OM) and Scanning Electron Microscopy(SEM).It was observed that the grain structure of α-Al in A206 alloy was changed from large dendritic crystal to small equiaxed one and the grain size was decreased from 164 μm to 26 μm with addition of Al2O3 nanoparticles.In addition,large number of flake-like(Fe,Mn)-rich intermediate phases were formed and coarse CuAl2 phases were eliminated in A206/1% Al2O3 aluminum composite,which significantly decreases its HCS.

Charpy Impact Properties of C/C and C/SiC Composties

YAN Ke-fei, ZHANG Cheng-yu, QIAO Sheng-ru, HAN Dong, LI Mei

2011, 31(2): 95-98.

[Abstract](1238) [PDF 1336KB](238)

Abstract:
The charpy impact properties of C/C and C/SiC composites were investigated.The specimens were impacted with the knife radius of 2 mm at a linear velocity of 2.9 m/s.The fracture morphologies were examined by Optical Microscope and Scanning Electron Microscope.The results indicate that a linear relationship is present between the impact energy and the density of both composites.The composites with higher density failed at smaller impact energy and their fractured surface are characteristic of few pull-out fibers.Whereas,the fractured surface is rougher for the sample with a lower density,in dicating a large amount of fibers or fiber bundles were pulled out from the matrix.

2011 Vol. 31, No. 2