航空材料学报

DU Yu-xuan, ZHANG Xin-ming, YE Ling-ying, LUO Zhi-hui

2007, 27(2): 1-5.

[Abstract](1172) [PDF 647KB](309)

Abstract:
The microstructure of an Al-Cu-Li alloy was investigated by optical microscopy and transmission electron microscopy,and the superplastic behavior of both samples subjected by conventional rolling processing and thermo-mechanical processing was studied by tensile test at elevated temperatures.It was found that Al-Cu-Li alloy could achieve elongation-to-failure of 94%~130% after a short time molten salt bath annealing.In this case,the intragrain deformation played the predominant role due to being lack of high angle grain boundaries.On the other hand,the optimal elongation-to-failure of thermo-mechanical treated sample was 630% measured by condition of T=490℃,ε=10-3s-1.A mix of intergrain and intragrain deformation prevailed in the sample aged for 24h,while grain boundary sliding was presented in the sample aged for 48h.Furthermore,the thermo-mechanical treated samples without recrystallization annealing showed a better superplasticity.

High Temperature Oxidation Behavior of a Ni₃Al Base Alloy Containing High Contents of W and Mo

LI Qing, SONG Jin-xia, XIAO Cheng-bo, WANG Ding-gang, YU Qian, HAN Ya-fang

2007, 27(2): 6-12.

[Abstract](1275) [PDF 2014KB](316)

Abstract:
The isothermal oxidation behavior of a Ni3Al base alloy containing high contents of W and Mo at 1050℃ was studied.The morphology of oxide scale of this alloy after oxidized for various time were observed by the scanning electron microscope,and types and amounts of the oxides were also analyzed by a X ray diffraction-meter.The results showed that the oxidation kinetic of this alloy didn’t follow the parabolic rule,and the substitution of W for some Mo could improve the oxidation resistance of the alloy at 1050℃ in some extent.Oxidation products after oxidized at 1050℃ for 100h were mainly NiO,NiAl2O4 and NiWO4.Cracks were found at outer NiO oxides and the inner multi-oxides interfaces in large areas during the process of cooling after oxidized for only 1h,which might attributed to the weak connection of the two layers leading the spallation of the outer NiO layer in the end.An inner oxidation resistance NiAl2O4/Al2O3 formed gradually with time between the alloy and oxides interface,and became almost continuously after 100h,which reduced the oxidation rate of the alloy effectively.

Test Research of Residual Strength on Aluminum Panels with Multiple Site Damage

WANG Chuan-sheng, ZHANG Jian-yu, BAO Rui, FEI Bin-jun

2007, 27(2): 13-17.

[Abstract](1169) [PDF 797KB](393)

Abstract:
Tests of residual strength on aluminum panels with multiple site damage(MSD)were conducted.Three different kinds of typical specimens were used,which had multiple cracks under the same stress level.The failure load was recorded when the test specimens were broken.Five different failure criterions were used to predict the failure load,and the predict results were compared with the test results in order to study the validity of these failure criterions.The results indicate that the Swift and average stress criterion can give better results than net ligament loss,CTOD criterion and the fracture mechanics criterion.

Effect of Electromagnetic Stirring on the Shape, Structure and Mechanical Properties of Al-Cu Alloy MIG Weld

GUO Xu-ming, YANG Cheng-gang

2007, 27(2): 18-21.

[Abstract](1239) [PDF 545KB](444)

Abstract:
Effects of electromagnetic stirring on the shape,structure and mechanical properties of pulse metal inert gas(MIG) weld of 2219 Al-Cu alloy were investigated.The results show that electromagnetic stirring modifies the shape of aluminum alloy MIG weld,the finger-like shape penetration of weld changing to elliptical penetration.Electromagnetic stirring promotes the coarse and oriented columnar grains and the dendrites transforming into the equiaxed grains through increasing heterogeneous nuclei in weld metal and decreasing temperature gradient just ahead of the solid-liquid interface. As a result,the microstructures of weld are refined and the strength and ductility are increased.

Influence of Recrystallized Layer on High Cycle Fatigue Life of Directionally Solidified Superalloy

HE Biao, LI Yun-ju, ZHANG Wei-fang, LU Yu-xiang

2007, 27(2): 22-24.

[Abstract](1167) [PDF 423KB](329)

Abstract:
Using cantilever-rotation-bending method,the influence of recrystallized layer formed by shot peening and heat treatment on high cycle fatigue life of directionally solidified DZ4 superalloy was studied.The results showed that recrystallized layer would formed in the DZ4 superalloy after predeformationg and high-temperature heat treatment,and recrystallized layer would weaken the high cycle fatigue life of DZ4 to a certain extent.In a certain extent of the pressure of shot peening,along with the increase of the pressure of shot peening,the fatigue life was first reduced and after increased.

Effect of Anodizing on Fatigue Performance of Aeronautic Aluminum Alloys

CAI Jian-ping, LI Bin, LIU Ming-hui, XIONG Jia-jin, ZHENG Liang

2007, 27(2): 25-28.

[Abstract](1271) [PDF 1157KB](396)

Abstract:
The effect of sulfuric acid,chromate acid and boric/sulfuric acid anodizing on fatigue performance of aeronautic aluminum alloys was studied by using S-N curve.The results illustrated that,different anodized cladding aluminum alloys had almost same fatigue limits;however,sulfuric acid anodizing greatly decreased fatigue limits of aluminum alloys,chromate acid also decreased fatigue limits of materials;boric/sulfuric acid anodizing did not decrease fatigue limits of aluminum alloys.The reason of above results was discussed.

Investigation of the Microstructures and Thermal Barrier Properties of YSZ Thermal Barrier Coatings

MU Ren-de, HE Li-min, HE Shi-mei, LU Feng, TAO Chun-hu

2007, 27(2): 29-32.

[Abstract](1145) [PDF 1060KB](403)

Abstract:
Thermal barrier coatings(TBCs) with Y2O3 paritally stablized zirconia(YSZ) ceramic top layer were deposited on the DZ125 superalloy substrates by using electron beam-physical vapor deposition(EB-PVD) technology.The microstructures of the EB-PVD TBCs were investigated by scanning electron microscopy(SEM),and laser pulse method was used to evaluate their thermal diffusion coefficients.Prior to the coefficient measurement,several thin sheltered layers on the surface of TBCs were adopted to prevent laser beam from penetrating the ceramic top layer.It was found that EB-PVD TBCs presented a typical columnar morphological features perpendicular to the substrate/coating interface.The thermal diffusion coefficient of the EB-PVD ceramic top layer slowly decreased with the elevation of the testing temperature,whereas the coefficient of the substrate increased rapidly.The coefficient value of the ceramic top layer was less than one third of the value of substrate at room temperature,and was about one sixty-seventh at 1200℃.With proper shelter layers,the instability and penetration issues in thermal diffusion coefficient measurement were resolved perfectly.If the sheltering requirement was satisfied,the variance of the shelter layer materials did not affect the measuring results in this study.

Effect of Processing Condition on the Tribological Property of Sputtered TiAlN Thin Films

LUO Fei, HE Xin, YANG Hui-sheng, GAO Ke-wei, WANG Yan-bin

2007, 27(2): 33-36.

[Abstract](1308) [PDF 220KB](308)

Abstract:
TiAlN thin films were deposited on high speed steel substrate by reactive magnetron sputtering.The microstructure was characterized by X-ray diffractometer.Friction coefficient of the films was measured on the UMT micromechanics test system.The effect of Al content,direct current negative bias and post treatment on the friction coefficient of the films was studied.The result showed that all the films were composed of fcc structure and hcp structure.With the increase of Al content,the proportion of fcc structure decreased.The increase of the Al content also caused the enhance of hardness and the decrease of the friction coefficient between the TiAlN thin films and GCr15 ball.The introduce of the direct current negative bias and post treatment bettered the friction resistant property observably.

High-Temperature Oxidation Resistance of Chromium Carbide/Ni₃Al Composite

LUO He-li, LI Shang-ping, FENG Di, CAO Xu, ZHANG Xi-e

2007, 27(2): 37-41.

[Abstract](1328) [PDF 1267KB](249)

Abstract:
The oxidation resistance of chromium carbide/Ni3Al composite and conventional high temperature wear-resistant material stellite 12 alloy at 1000℃ was investigated comparatively.For stellite 12 alloy,the oxides scale mainly consisted of Cr2O3,and some of them scaled off the alloy.For chromium carbide/Ni3Al,the protective oxides that mainly consisted of α-Al2O3 were formed and the chromium carbides exhibited good anti-oxidation stability and oxidation synergism with Ni3Al matrix.The analyse showed that the chromium carbides were dissolved during welding and some dissolved Cr enter into Ni3Al matrix.The existence of Cr promotes α-Al2O3 formation,which improved the oxidation resistance of the composite obviously.The oxidation rate of the stellite 12 alloy was two times greater than that of the composite in air.The different oxidation behavior of two materials was mainly attributed to different oxides scale characters.

Study on the Fabrication and Properties of the 2D C_f/SiC-Si Composites

LIU Jing-yu, CHEN Zhao-hui, JIAN Ke

2007, 27(2): 42-45,51.

[Abstract](1159) [PDF 706KB](210)

Abstract:
Based on the high temperature and short-term oxidation environments,2D Cf/SiC-Si composites were prepared by precursor infiltration and pyrolysis.Effects of the pyrolysis temperature at the first cycle and Si content on the mechanical properties and anti-oxidation properties were investigated.The results showed that 2D C/SiC-Si composites exhibited weak interface bonding and better mechanical properties when the pyrolysis temperature of the first cycle was 1200℃,and the flexural strength and fracture toughness reached 305.4MPa and 15.7MPa·m1/2,respectively.At the same time,with the increase of the Si content,the mechanical properties of the composites decreased slightly,while the anti-oxidation properties of the composites were remarkably improved.The better anti-oxidation properties of the composites were attributed to the decrease of the free carbon in the composites and Si could transfer to SiO2 at high temperature in air which could heal the crack and prevent the diffusion of the oxygen.

Influence of Warm and Wet Environment on Adhesive Shear Strength of Sulfur Silane Coupling Agent Pretreated Aluminum Sheet/Epoxy

CHEN Ming-an, XIE Xuan, LI Hui-zhong, YANG Xi, ZHANG Xin-ming

2007, 27(2): 46-51.

[Abstract](1156) [PDF 1253KB](314)

Abstract:
The adhesive shear strengths, the load-displacement curves and the features of the shear fracture surfaces of sulfur silane coupling agent pretreated LY12 aluminum alloy sheets/epoxy immersed in boiling water and NaCl water solution respectively were investigated.The results show that immersion in boiling water for 20～60h the adhesive shear strengths are about 15.3MPa,and for 80h it is 13.39MPa,which is 66.3% of the initial value.When immersion in NaCl water solution at 50℃ the adhesive shear strengths increase.The maximum value is 21.8MPa for immersion of 60h,and then decrease to 18.4MPa with the immersion time to 180h.Fewer cracks are observed on the fractured surfaces after treatment in boiling water and in the NaCl water solution as compared to that of without immersion treatment.These could be ascribed to plasticization and strengthening of the epoxy respectively.

Irregular Section Carbon Fiber and its Effects on Mechanical Properties of Composite

XU Zhi-wei, HUANG Yu-dong, LIU Li, ZHANG Chun-hua

2007, 27(2): 52-57.

[Abstract](1230) [PDF 1251KB](370)

Abstract:
A kind of irregular section carbon fiber and its epoxy composite were involved.The surface performance and fabric of carbon fiber were tested,and mechanical properties,damaged pattern and fiber arrange way of composite were analyzed.The irregular section fiber and its composite were compared with T300 and T300/epoxy composite.It was shown that the cross-section shape of irregular fiber was kidney-shaped,the surface of irregular fiber was smooth,the surface chemical activity of irregular fiber was weak and the degree graphitization of irregular fiber was low.But it was revealed that the irregular fiber had a larger specific surface area and greater wetting ability with liquid than T300.By the mechanical property measure,the performance of irregular fiber/epoxy composite approached to T300/epoxy composite.It was indicated by SEM that the interfacial adhesion of irregular carbon fiber/epoxy composite was poor and the distribution of irregular fiber in composite was uneven.

Electromagnetic Characteristics of Carbon Black Doped with Nanometer Manganese Dioxide

ZHANG Xin, LIU Shun-hua, DUAN Yu-ping, GUAN Hong-tao, WEN Bin

2007, 27(2): 58-61.

[Abstract](1349) [PDF 484KB](323)

Abstract:
A novel absorbing medium of carbon black doped with nanometer sized manganese dioxide were prepared.The microstructure,dielectric constant(ε′,ε″) and microwave absorption property of samples were measured by means of transmission electron microscopy(TEM),transmission/reflection coaxial method from 2GHz to 18GHz and HP 8720B vector network analyzer(VNA).The results show that manganese dioxide belongs to dielectric loss medium with flake and strip shaped while carbon black belongs to erratic current loss medium with sphere and multi-hole shaped.It is notable that manganese dioxide has a great effort to intensify microwave absorption capability of carbon black due to not only its flake and strip shaped microstructure which can increase the reflection and scatter cross section of electromagnetic wave but also its high resistance which can improve the impedance matching of samples.

Characterization of Boride Ceramic Powders Prepared by SHS

YU Zhi-qiang, YANG Zhen-guo

2007, 27(2): 62-67.

[Abstract](1274) [PDF 887KB](250)

Abstract:
Self-propagating high-temperature synthesis(SHS) method with reductive process was used to produce TiB2,TiB2-Al2O3 and ZrB2-Al2O3,etc.borides and composite ceramic powders.X-ray diffraction,XPS,SEM and TEM analysis means were used to analyse microstructure of the synthesized powders.The results showed that TiB2,ZrB2 and Al2O3 as primary crystalline phase existed in synthesized powders,respectively.By comparison,the particle size distribution of TiB2 monolithic powder was wider.Owing to the high temperature of SHS,most of them formed aggregates and made the macroscopical particle size big (5μm).While the particles size distribution of TiB2-Al2O3and ZrB2-Al2O3 composite powders was obviously narrow and free-agglomerate,and the composite particles decreased in the particle size.It could be suggested that it was mainly related to the good interface formation between the different particles in composite powders during the synthesis reaction.

Preparation and Structure Properties of ZnMnO₃ and LaZnMnO₃

ZHOU Zheng-you, LUO Guang-sheng, WU Ben-wen, JIANG Feng-yi

2007, 27(2): 68-73.

[Abstract](1309) [PDF 771KB](414)

Abstract:
The preparation and structural properties of ZnMnO3 and La1-xZnxMnO3 were investigated.The results indicate that ZnO react MnO2 to form ZnMnO3 spinel structure above 1300℃ and 12h.Solid-state reaction is closely related to sintering temperature and time.La1-xZnxMnO3 was prepared by solid reaction of ZnO,MnO2 and La2O3 with different ZnO concentrations.X-ray diffraction patterns shows that La1-xZnxMnO3 has perovskite structure when sintering temperature and time exceeds 1300℃ and 12h,respectively.The concentration is between 50% to 70%,a few new diffraction peaks appear,which indicates a new phase probably formed.further study is necessary to investigate the new phase and magnetoresistance effect.

New Advancement of Oxidation Protective Coatings for C/C Composites

HUANG Jian-feng, ZHANG Yu-tao, LI He-jun, ZENG Xie-rong, CAO Li-yun

2007, 27(2): 74-78.

[Abstract](1319) [PDF 1241KB](737)

Abstract:
The recent advancement of the oxidation protective coatings of C/C composites in China was reviewed.New technologies and new improvements of the traditional coating preparation technologies for C/C composites were introduced.According to the application conditions of C/C composites,the development trend of anti-oxidation coatings was also proposed.It was showed that the present research results could not meet the requirements of the coated C/C composites in severe work environments.The further researches would be focused on the preparation of suitable coating that could protect C/C composites from oxidation from room temperature to 1700℃ in high speed gas-fired environments.To reduce the cost of preparation,the coating that could works at 1800℃ for long time should be exploited.

2007 Vol. 27, No. 2