航空材料学报

Effect of Element Hf and Cooling Rate during Solidification on Low Cycle Fatigue Properties of Directionally Solidified Superalloys

ZHENG Yun-rong, XIE Ji-zhou

2009, 29(6): 1-7.

[Abstract](1148) [PDF 1380KB](209)

Abstract:
The directionally solidified specimens of DZ22 superalloy and its Hf-free version were prepared by rapid or slow cooling solidification.The low cycle fatigue (LCF) properties of specimens at 760℃ and 1.0~1.4% total strains were determined.The optical metallography,quantitative metallography and scanning electron microscopy (SEM) were applied to observe the original microstructure,the changes of LCF microstructure and the fracture surface characteristics of specimens.The results show that the addition of Hf significantly increases LCF life of DZ22 alloy and the slow cooling solidification seriously impairs LCF properties of alloys.Most of LCF cracks appear in the late half lifetime and mainly distribute at the columnar grain boundaries,interdendrites,interfaces of slipping bands and MC carbide.The appearance of slipping bands can be considered to be the early signal of LCF damage.It is important characteristics of LCF rupture at intermediate temperature for this kind of alloy that the cluster of MC carbides cracks by slipping impact,than cracks propagate to periphery and leave the fatigue striations.In present paper,the practical operations to prolong the LCF lifetime by means of decreasing or refining MC carbides are also discussed.

Effect of Al on High Temperature Oxidation Resistance of Cr-20Nb Alloy

HUANG Yi, LU Shi-qiang, ZHENG Hai-zhong

2009, 29(6): 8-12.

[Abstract](903) [PDF 387KB](238)

Abstract:
The influence of Al on the high temperature oxidation of Cr-20Nb alloys,which were fabricated by mechanical alloy and hot press,has been studied at 1100℃ and 1200℃ in air,respectively.The results indicate that the proper addition of Al promote the formation of AlNbO4 complex oxide which retard the volatilization of Cr2O3 scales.Thus the compactability of Cr2O3 scales and the adherence of the oxide scale are improved,which lead to the oxidation resistance remarkably improved.The results also show that the oxidation kinetics of Cr-20Nb alloys with different Al content is similar to parabolic law.

Corrosion Behavior of Rapidly Solidified Mg-5Zn-1Y-0.6Zr Alloy

LIU Guang, ZHANG Zhen-zhong, CHEN Qian, YIN Chang-hao, ZHANG Shao-ming

2009, 29(6): 13-17.

[Abstract](1231) [PDF 1152KB](203)

Abstract:
The effects of rapidly solidification on the microstructure and the corrosion behavior of Mg-5Zn-1Y-0.6Zr alloys in the 3.5% NaCl solution were investigated.The microstructure and the corrosion surface of the alloy were observed using OM and SEM.The results show that the amorphous phase occurred and alloy microstructures are refined and more uniformed by rapidly solidification,then the corrosion resistance of the alloy is improved.At room temperature,the corrosion rate increased firstly and then reduced with increase of time.The main corrosive product was mainly Mg(OH)2 using XRD.Polarization curve test result shows the corrosion resistance is better as the cooling rate is higher.

Microstructure Features of Laser Deposited Ti-6Al-2Zr-Mo-V Alloy

HE Rui-jun, WANG Hua-ming

2009, 29(6): 18-22.

[Abstract](891) [PDF 1041KB](468)

Abstract:
Laser melting deposition (LMD) process was used to fabricate Ti-6Al-2Zr-Mo-V alloy directly.The metal powders were continuously melted and rapidly solidified layer upon layer directly into the near-net shape structure.The elements were fully melted and uniformly mixed in the molten pool that homogenized dense microstructure was obtained.Laser deposited Ti-6-Al-2Zr-Mo-V is characterized by a fine α/β lamellar microstructure with various random orientations,which should be related to the rapid solidification and phase transformation during the process.The influence of deposition layer on the fatigue strength is discussed.

Controllable Dendrite Growth Technology of Preparing Foamed Metal Material

WANG Gui-feng, HUANG Yin-hui, TIAN Zong-jun, LIU Zhi-dong, GAO Xue-song

2009, 29(6): 23-27.

[Abstract](1145) [PDF 736KB](280)

Abstract:
With the combination of fractal and electrodeposition,fractal growth process of dendrite in electrodeposition with parallel plate electrode was successfully stimulated.Using parallel plate Ni as anode and graphite plate as cathode,the fractal growing dendrite of Ni was manufactured to test the stimulation by fixed-point jet-electrodeposition.At a later time,the porous metal was manufactured by altering fractal growing of Ni in scanning jet-electrodeposition.The result proves that the porous metal can be successfully manufactured by scanning jet-electrodeposition.It would be helpful to use this method to manufacture high performance porous metal.

Effect of Over-Length Aging on Properties of 7075 Alloy

CHEN Xiao-ming, SONG Ren-guo, ZHANG Yu, HE Yuan, ZHAO Jian, LI Jie

2009, 29(6): 28-32.

[Abstract](1247) [PDF 1205KB](574)

Abstract:
The aging behavior,mechanical properties,stress corrosion resistance properties and microstructure of 7075 aluminum alloys with overlength aging were studied by means of Rochwell hardometer,electronic tensile machine,impact testing machine,scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS).The results show that the hardness,strength properties all has double peaks.Although the hardness and strength of two peaks is almost equal,the stress corrosion resistance properties of the alloy at the second ageing peak are higher than those at the first ageing peak.A "phase-changing-Mg-H" theory is put forward firstly,and the mechanics of high-SCR for 7075 alloy second-peaking aged is explained properly by it.

Microstructure and Creep Features of FGH95 Powder Nickel Base Superalloy after Heat Treatment

TIAN Su-gui, LIU Yang, ZHOU Xiao-ming, ZHAO Zhong-gang

2009, 29(6): 33-37.

[Abstract](1082) [PDF 787KB](283)

Abstract:
By means of the measurement of creep curves and microstructure observation,an investigation has been made into the microstructure and creep behaviors of FGH95 powder nickel-base superalloy.Results show that,after solution treated,microstructure of the alloy consists of the finer γ’ phase and γ matrix,and the finer (Nb,Ti)C carbide particles is discontinuously precipitated within the grains and grain boundaries.In the range of the applied temperatures and stresses,the alloy displays an obvious sensibility of the applied temperatures,and the creep activation energy and stress exponent of the alloy during steady state stage are calculated to be Q=542.07kJ/mol and n=14.8,respectively.The deformation mechanism of the alloy during creep is that the double orientation slipping of dislocation are activated in the alloy.The 110 super-dislocation which shears into γ’ phase may be decomposed into two of (1/3)112 super-shockleys dislocation to form the dislocation configuration of the partial+stacking fault.And in the further,the twinning plane activated during twinning deformation is determined as (111) plane.The boundaries and (Nb,Ti)C carbide particles which is discontinuously precipitated along the grain boundary may effectively hinder the movement of dislocation,which is thought to be one of the main reasons for the alloy displaying a better creep resistance.

Experiment Method of 2D70 Aluminum Alloy Larger Dimension Bar Hardenability in Commercial Process

WANG Guo-jun., XIONG Bai-qing, ZHANG Yong-an, NIE Bo, CONG Fu-guan

2009, 29(6): 38-42.

[Abstract](1163) [PDF 560KB](314)

Abstract:
The variation curve of hardness and mechanical property with different distance from core of the 2D70 aluminum alloy larger dimension bar has been drawn by monitoring different site temperature changes on the same cross section during quenching process in lab,and through testing and analyzing hardness and mechanical property of the materials.The same variation curve of the same specification material which produced by commercial process has been described.The curves of different material have been compared and analyzed.The feasibility of the experiment method applied to commercial process product has been discussed.The study shows that the temperature of core and edge on the cross section of the 2D70 aluminum alloy of φ250mm×250mm during quenching process is uniform.The general cooling velocity during quenching process is 4℃/s,The sufficiency solution has been occurred.The quenched depth of the alloy is greater than 125mm.

Compatibility of SiC_p/Al Composites with Titanium Alloy Integrated Synchronously by Pressureless Infiltration Technique

CUI Yan, ZHANG Lei, ZHAO Hui-you

2009, 29(6): 43-47.

[Abstract](1278) [PDF 523KB](230)

Abstract:
High volume fraction SiCp/Al composites and titanium alloy component (cylinder) were integrated synchronously by Al melt pressureless infiltration technique,and microstructures and properties of the scale-span and ultra-hybrid aluminum metal matrix composite were investigated,in particular,the compatibility of SiCp/Al composite with titanium alloy component.The results show that the composites possess excellent properties,homogeneous and full dense microstructures.The interface between SiCp/Al composite and titanium alloy is bonded tightly,appearing Ti diffusion into Al matrix in a limited distance and continuous interfacial reaction product thin layer without crack or porosity,the reaction product was identified as Al2Ti by SEM and XRD analysis.The shear strength of the interface is more than 200MPa,and it can meet the requirements of machining assembly hole on titanium alloy component in composites.

Joining of C_f/SiC Composite to Ti Alloy using AgCuTi-W Composite Filler Materials

XIONG Jin-hui, HUANG Ji-hua, XUE Hang-yan, ZHANG Hua, ZHAO Xin-ke, LIN Guo-biao

2009, 29(6): 48-52.

[Abstract](1217) [PDF 941KB](268)

Abstract:
Cf/SiC was successfully joined to Ti alloy with AgCuTi-W mixed powder by some suitable brazing parameters.Microstructures of the brazed joint were investigated by SEM,EDS and XRD.The mechanical properties of the brazed joints were measured by mechanical testing machine.The results showed that Ti element in the interlayer can reaction with the brazed composite,a mixture of Ti3SiC2,Ti3Si and TiC composites finally formed the reaction layer between composite and interlayer.Ti alloy constantly dissolves and Cu diffuses into the Ti alloy,forming the diffusion–reaction layers between interlayer and Ti alloy.The performed joints have dense bonding layers reinforced by W.These composite brazing layers relaxed the thermal stress of the joint effectively.These characteristics were beneficial to the joint,of which the shear strength were remarkably highly than the optimal shear strengths of the joint brazed with pure AgCuTi.

Study on Microstructure and Mechanical Properties of Fine Grain TC21 Alloy in TIG

ZHOU Shui-liang, TAO Jun, GUO De-lun

2009, 29(6): 53-58.

[Abstract](1138) [PDF 1008KB](261)

Abstract:
Fine grain TC21 alloy with various grain sizes were welded by conventional TIG welding.The mechanical properties of welded joint were investigated.The results showed that the tensile strength of welded joint of fine grain TC21 with various grain sizes was about 95% one of the base metal,the weldability of TC21 alloy was good by and large.But welded joint was seriously brittle,the specific elongation and reduction of cross section area of welded joint were more lower than that of the base metal.The microstructure of fusion zone (FZ)and heat-affected zone(HAZ) were similar,which were called α’ martensites.With the same parameters,the microstructure of FZ and (HAZ) of 2μm TC21 alloy were lamellar or long granular α’ structures,whereas the microstructure of welded joint of 7μm TC21 alloy was needle or small granular α’ structure,which α’ clusters was small and crossed.Hardness measurements showed there was a softened zone in fine grain heat-affected zone(FHAZ) near the base metal,the hardness of softened zone was the lowest.However,the boundaries between FZ and coarse grain heat-affected zone(CHAZ) of welded joint was another softened zone,but hardness decreased slightly in this zone.Tensile fractures of welded joint presented character of quasi-cleavage crack.Cleavage features of fractography of weld joint were more obvious with increasing grain size of the base metal.

Effect of Technological Parameters on Formation Process of Ceramic Films Fabricated by Micro-arc Oxidation

SUN Zhi-hua, LIU Ming, GUO Da-peng, GUO Meng-qiu, LU Feng, TAO Chun-hu

2009, 29(6): 59-65.

[Abstract](1201) [PDF 928KB](383)

Abstract:
Effect of technological parameters,such as anodic current density(Ia)/cathodic current density (Ic),frequency,cathodic duty ratio,on the formation process of micro-arc oxidation films on 2A12 aluminum alloy are studied and the microstructure,morphologies,composition and phase constituents under different oxidation time were studied by scanning electron microscope (SEM) and X-ray diffraction (XRD).The results show that film thickness increases with the current density and the increasing of Ic is beneficial to the film growth.With frequency and cathodic duty ratio,the film thickness increases firstly then decreases.The thickness of total film increases linearly and the growth speed towards outer space is faster than that towards substrate with the oxidation time.The results of SEM show that many crater-mouth like traces formed by the plasma discharge are observed on the coatings surface,and the thickness on the cross section become same and the film/substrate interface even with MAO time.The results of XRD reveal that the content of γ-Al2O3 in the ceramic coatings decreases,and the content of α-Al2O3 increases with oxidation time.

Improvement of Surface Porosity and Properties of MAO Ceramic Coatings by Incorporation of SiO₂ Nanoparticles

SUO Xiang-bo, MA Shi-ning, QIU Ji, LüQing-xing

2009, 29(6): 66-69.

[Abstract](994) [PDF 973KB](474)

Abstract:
Ceramic coatings incorporated with SiO2 nanoparticles were fabricated on 7A52 aluminum alloy during micro-arc oxidation by mixing SiO2 nanoparticles into the electrolyte.The porosity and properties of the ceramic coatings were investigated.The results show that coatings embedded with SiO2 nanoparticles exhibit lower porosity and improved compactness,which lead to higher microhardness and better corrosion resistance.The enhancement of compactness can be attributed to SiO2 nanoparticles deposited in discharge pores during the micro-arc oxidation process.

Microstructure and Properties of NiCr/Cr₃C₂-BaF₂·CaF₂ Coatings Prepared with Three Kinds of Thermal Sprayed Technologies

HUANG Chuan-bing, DU Ling-zhong, ZHANG Wei-gang, WANG Lu, HOU Guang-ku

2009, 29(6): 70-76.

[Abstract](1274) [PDF 1854KB](365)

Abstract:
Microstructures,composition,porosity,hardness,bonding strength and tribological properties of NiCr/Cr3C2-BaF2·CaF2 coatings prepared with plasma spraying (APS),detonation spraying (DS) and high velocity oxy-fuel spraying (HVOF) was systematically investigated.The results show that using coated spray powders,the decarburization of carbide,oxidation and ablation are reduced in thermal spray process.The NiCr/Cr3C2-BaF2·CaF2 coatings deposited by HVOF and detonation spraying have higher density,hardness and bond strength with comparison to plasma spraying.The friction coefficients of three kinds of NiCr/Cr3C2-BaF2·CaF2 coatings decrease with the increasing temperatures,and the high temperature friction coefficients are significantly lower than that at room temperature.The friction coefficients of HVOF and detonation spraying coatings are lower than plasma spraying coating,and HVOF and detonation spraying coatings show better wear-resistance.The friction coefficients and wear rates of three coatings as well as the wear rates of coupled Si3N4 balls are reduced due to the formation of BaF2·CaF2 lubrication layer at elevated temperatures.

Effect of EB-PVD Thermal Barrier Coating on Mechanical Properties of IC10 Alloy

WU Xiao-mei, HE Shi-mei, LI Jian-ping, HE Li-min

2009, 29(6): 77-80.

[Abstract](1238) [PDF 1094KB](291)

Abstract:
The Y2O3 stabilized ZrO2 thermal barrier coatings with arc ion plated NiCrAlYSi bond coating were deposited by EB-PVD technique on the IC10 alloy substrate.The effect of YSZ thermal barrier coating on the tensile strength,yield strength at 900℃ and the rotating bending fatigue life were studied.Compared IC10 alloy with thermal barrier coating to IC10 alloy,the results of the stress rupture life under 980℃/200 MPa conditions,the tensile intension and yield intension at 900℃ and the rotating bending fatigue life under 800℃/447 MPa were identical.But it’s room temperature tensile strength and yield strength decreases in some sort.So the EB-PVD TBCs process does not affect the mechanical properties of IC10 substrate.

Quantitative Characterization of Subgrain Structure of Martensitic Cr Steel

ZHAO Qing, QIN Yong, ZHU Xiao-guang, FENG Chang-jie

2009, 29(6): 81-84.

[Abstract](1225) [PDF 897KB](209)

Abstract:
Quantitative characterization of the martensitic Cr steel subgrain was conducted by TEM under different crept states.The crept subgrain’size distribution and their microstructure,as well as their effects on the microhardness were investigated.The results show that the subgrain of the martensitic Cr steel are coarsened under high stress creep,and more coarsened under low stress creep.The coarsened subgrain structure in the crept steel decreased their microhardness and their relationship obeyed the Hall-Petch formula.

Effect of Ho₂O₃ Doped on Micro-Structures and Properties of In-Situ HoAl-Al₂O₃/TiAl Composites

XU Hong-ya, WANG Fen, XIE Yu-xing, ZHU Jian-feng

2009, 29(6): 85-88.

[Abstract](1230) [PDF 341KB](196)

Abstract:
HoAl-Al2O3/Ti aluminide composites reinforced by Ho2O3 were prepared by in-situ hot-pressing method with the exothermic reaction of Al,Ti,TiO2 and Ho2O3 powder.The effect of Ho2O3 doping on the microstructures was analyzed by XRD,SEM.Bending strength and fracture toughness properties were tested.The refinement mechanism of rare-earth oxide was investigated as well.The results show the phases of the composites are composed of TiAl,Ti3Al,Al2O3 and HoAl.The HoAl particles distributed at grain boundary of the matrix and Al2O3 particles.At the same time,it restricted particle size and increased particle dissemination of the HoAl,Al2O3.The mechanical property of composites reinforced by Ho2O3 were increased.

Microstructure and Properties of in-situ Synthesis TiC Reinforced 2A14 Al Matrix Material

ZHU Li-jie, SUN Yang-shan, ZUO Ai-jun, XUE Feng

2009, 29(6): 89-93.

[Abstract](1045) [PDF 741KB](221)

Abstract:
TiC particulate reinforced 2A14 aluminum alloys were prepared,using the technique of in-situ synthesis reaction.Microstructure revealed that TiC particles in the alloys were equiaxed morphology with size of 1~3μm in diameter.Addition of TiC particles to 2A14 aluminum alloy caused significant refinement of as cast microstructure and increase of tensile strength,but decrease of ductility of the alloy.At the elevated temperature of 150℃,the variation of tensile properties with addition of TiC particles were similar with that in ambient temperature.The wear resistance of the alloy was remarkably improved when small amount TiC particles was introduced.Under the condition of oil lubrication,the wear resistance of TiC particulate reinforced 2A14 alloy was much higher than that of some typical wear resistant alloys,such as wear resistant brass,ZA30 zinc alloy and Al-30Si high silicon alloy.

Acoustic Absorption Properties and Theoretics of Polyimide Foams

PAN Pei-chang, ZHAN Mao-sheng, SHEN Yan-xia, WANG Kai

2009, 29(6): 94-97.

[Abstract](1290) [PDF 1015KB](391)

Abstract:
The closed cell polyimide foams were fabricated by foaming the precursor balloons,and the foams’acoustic absorption properties were tested.The results show that the acoustic absorption properties of closed cell polyimide foams have the typical resonance acoustic absorption characteristic.The acoustic absorption properties of polyimide foams were researched,and the influence of thickness and density on its acoustic absorption properties were also studied,the acoustic absorption theoretics of polyimide foams was analyzed.The combination of closed cell and open cell polyimide foams can notable enhance the acoustic absorption coefficient.

Processing Conditions and Mechanical Property of Long Glass Fiber Reinforced Injection-moulded PEEK Composites

WU Xin-ming, QI Shu-hua, HE Jie, LI Sha-sha, MO Jun-lian

2009, 29(6): 98-101.

[Abstract](1197) [PDF 752KB](403)

Abstract:
The processing conditions of 30% long glass fiber reinforced PEEK including cooling rate,forming pressure,forming temperature,mold temperature and mechanical property were studied by using injection-moulding method.Experimental results prove that the tensile strength of PEEK composites is to 81MPa,the impact strength is to 62.7MPa,the surface is smooth and PEEK composites is excellent comprehensive properties when the cooling rate is middle slow,forming pressure is 120MPa,forming temperature is 375℃,425℃,425℃ and mold temperature is 180℃.

Design of Single and Double-layer Microwave Absorbing Materials Containing Left-handed Materials

WANG Zheng-ping, ZHANG Zhen-hui, WANG Li-hui

2009, 29(6): 102-106.

[Abstract](1137) [PDF 2178KB](288)

Abstract:
Design schemes of single layered and double layered microwave absorbers with left handed materials and different structures were proposed.The physical models of the absorbers were built up to describe their wave-absorbing properties.Their working principles were successively derived employing transform matrix method,the design criteria,which had to follow during the design procedures,for each scheme of them were stated.General processes of designing the wave-absorbers were introduced,some theoretically derived formulae were given,which may be used in the design.

Study on Accelerated Ageing of Aeronautical Perspex(PMMA) in Ultraviolet

CHEN Xin-wen, PEI Gao-lin, JIN Yu-shun

2009, 29(6): 107-112.

[Abstract](1256) [PDF 1544KB](420)

Abstract:
The accelerated ageing experiment of Perspex (PMMA) YB-DM-11 were done for nearly two months in both 254nm and 313nm wave length ultraviolet.Tensile stress and mass were measured during the experiment.Thus the changing rules of both parameters were obtained.The samples structure difference were founded between before ageing and after ageing by methods of IR,TG/DTA,GPC and SEM.Analyzed results above all,the ageing mechanisms of PMMA in ultraviolet were clarified qualitatively.

2009 Vol. 29, No. 6