航空材料学报

Study on Mechanism and Kinetics of Die Forming and Sintering Utilizing Hydrogenated TC4 titanium alloy Powder

TIAN Ya-qiang, HOU Hong-liang, REN Xue-ping

2010, 30(5): 1-7.

[Abstract](1729) [PDF 637KB](186)

Abstract:
The kinetics problems of consolidation process of hydrogenation titanium alloy powder were studied by means of establishing regular tetrahedron model for powder sintering and deducing expression of sintering neck and relative density of hydrogenated titanium alloy powder with sintering kinetics experiment.The results show that the transport mechanisms of hydrogenated TC4 titanium alloy powder sintering process was changed from the main transport mechanisms of volume diffusion to the interaction transport mechanisms between volume diffusion and grain boundary diffusion.And according to the transport mechanisms of hydrogenated TC4 titanium alloy powder sintering process,the kinetics equation for the consolidation process of hydrogenated TC4 titanium alloy powder by die forming and sintering was obtained.The hydrogen content was the most important factor of effecting sintered body relative density of hydrogenated TC4 titanium alloy powder.

Effects of External Stress During Aging on Microstructure and Properties of Al-Cu-Mg-Ag Alloy

LIU Xiao-yan, PAN Qing-lin, CAO Su-fang, LU Zhi-lun, HE Yun-bin, LI Wen-bin

2010, 30(5): 8-13.

[Abstract](1635) [PDF 2583KB](265)

Abstract:
The effects of external stress during aging on the microstructure and properties of Al-Cu-Mg-Ag alloy were studied by hardness test,optical microscopy(OM) and transmission electron microscopy(TEM).The results show that completely recrystallization occurs in the alloys aged with and without stress.The morphology of the alloy is not changed when treated by stress-aged but the precipitations are changed greatly.Both θ' phases and Ω phases precipitate to some preferred orientation,showing character of stress-orientation.The precipitation of θ' phases is accelerated while that of Ω phases is restrained,and the hardness of the alloy is decreased to a small extent.This might be due to that the large amounts of dislocations during stress-aging provide sites facilitating heterogeneous nucleation of θ' phases.Thereby,Ω precipitations with the same chemical constituents of θ' phases are retained.This is verified by the phenomenon that the density of θ'phases is increased while that of Ω phases is decreased,and the hardness is reduced when Al-Cu-Mg-Ag alloy is pre-deformed 6% before aged.During the stress-aging,the existence of the dislocations disrupts the diffusion of the solution atoms,correspondingly distance the formation of the clusters and the co-clusters.As a result,the precipitations of the strength phases are delayed.

Influence of Direct Aged Treatment on Creep Behaviors of Hot Continuous Rolling GH4169 Superalloy

TIAN Su-gui, ZHAO Zhong-gang, CHEN Li-qing, YU hui-chen, LIU Yang, BAO Xian-yu, LIU Xiang-hua

2010, 30(5): 14-18.

[Abstract](1662) [PDF 615KB](383)

Abstract:
By direct aged treatment,creep properties measurement and microstructure observation,the influences of the direct aged treatment on the creep behaviors of Hot Continuous Rolling GH4169 Superalloy are investigated.Results show that the creep resistance of Hot Continuous Rolling GH4169 Superalloy may be obviously improved by directly aged treatment.Under the applied stress of 700MPa at 660℃,the creep life of the alloy is enhanced to 126h from 60h.In the range of the applied stresses and temperature,the creep activation energy and stress exponent of the alloy during steady state stage are measured to be 559.2kJ/mol and 17.6,respectively.During hot rolling,the deformation features of the alloy are the twinning and the double orientations slipping of the dislocation activated within the twinning regions.And the alloy displays a smaller grain size.After direct aged treatment,the finer phase is dispersedly precipitated in the matrix of the alloy,which is a main reason of enhancing creep life of the alloy.During creep,the deformation features of the alloy are the twinning and dislocation slipping activated in the matrix of the alloy.In the later period of creep,the micro-cracks are appeared in the grain boundaries regions vertical to the applied stress axis,and the micro-cracks are expanded along the boundaries as creep goes on,Which is thought to be the mechanism of the alloy crept up to fracture.

Research on Microstructure of High Speed Steel Prepared by Spray Forming

ZHANG Yong, ZHANG Guo-qing, LI Zhou, YUAN Hua, XU Wen-yong, LIU Na, GAO Zheng-jiang

2010, 30(5): 19-24.

[Abstract](1601) [PDF 1447KB](290)

Abstract:
The microstructure before and after heat treatment of high speed steel(HSS) T15 prepared by spray forming was researched.The result indicated that the high-quality billet of HSS T15 exhibited high-density,much fine grains than that of common HSS and segregation-free macrostructure.The average density of billet before heat treatment(HT) is 8.208g/cm3 which is 99.8% of theoretical density.The hardness of SFT15 billet was HRC56.5,after HIP and HT it was improved to HRC67,and fracture toughness was 11.8J/cm2.By means of Scanning Electron Microscopy(SEM) and transmission Electron Microscopy(TEM),we found that the structure of HSS SFT15 after heat treatment is constituted by tempered martensite and carbide.And most grain is less than 20μm.Much carbide whose structure is M6C is distributed in grains and grain boundary.

Structure and Properties of Diffusion Bonded TA2 to 1Cr18Ni9Ti Joints with Ni+Nb Composite Interlayer

LI Peng, LI Jing-long, XIONG Jiang-tao, ZHANG Fu-sheng

2010, 30(5): 25-29.

[Abstract](1568) [PDF 687KB](342)

Abstract:
Diffusion bonding in vacuum was carried out between commercially pure titanium TA2 and austenitic stainless steel 1Cr18Ni9Ti by using Ni+Nb composite interlayer at the temperature of 840℃,880℃ and 920℃ for 60min under 4MPa axial pressure.The tensile strengths of the joints were tested,meanwhile the fracture surfaces were analyzed by SEM and XRD.The microstructure and element distribution of the joints were analyzed by OM,SEM and EDS.The results show that Ni+Nb composite interlayer successfully suppresses interdiffusion of Ti and Fe,so that the sound joints were formed.Five reacted-layers are presented at the joint.They are FeCrNi solid solution,residual Ni,Ni3Nb,residual Nb,TiNb widmanstatten structure from 1Cr18Ni9Ti to TA2.The residual Ni is critical to strength of the joint,the strength reaches up to 261MPa and changes a less with temperature.

Effect on structure and Properties of Aluminium Alloy Containing Minor Scandium and Zirconium TIG Welded Joint by Using Different Filler Metals

WANG Shao-gang, WANG Zong-xiang, GU Bing-fang

2010, 30(5): 30-34.

[Abstract](1629) [PDF 631KB](255)

Abstract:
The microstructure and mechanical properties of aluminium alloy containing minor scandium and zirconium joint were investigated by using different filler metals in tungsten inert gas arc welding(TIG),and the optimized welding parameters were obtained in the experiment condition.The tensile test results show that the joint tensile strength with Al-Mg wire or base material wire is obvious higher than that of with Al-Si wire or pure Al wire.Microstructure analysis of welded joint suggests that the joint structure with Al-Mg wire or base material wire is dense and no weld defects such as micro-crack and inclusion can be found in weld metal,and the tensile fracture of joint presents the characteristics of toughness.XRD test indicates that there are some strengthening phases of Al3Sc,Al3Zr,Al3Zr4,and etc in the weld metal,which are advantageous to improve the joint strength.

Microstructures and Properties of Ti₃Al/Ti₃Al and Ti₃Al/GH536 Joints Using Ti-Zr-Cu-Ni Brazing Filler

CHEN Bo, XIONG Hua-ping, MAO Wei, CHENG Yao-yong

2010, 30(5): 35-38.

[Abstract](1590) [PDF 604KB](308)

Abstract:
Vacuum brazing of Ti3Al/Ti3Al and Ti3Al/GH536 joints using Ti-Zr-Cu-Ni brazing filler was carried out at 960℃ for 1min,10min and 60min and at 960℃ for 5min and 20min respectively.The results showed that the shear strengths were increased as holding time prolonged and the incremental value was about 10MPa for Ti3Al/Ti3Al joints.Ti3Al,NiTi2,CuTi3 phases formed in the brazing seams and the distribution of NiTi2 and CuTi3 brittle phases affected the mechanical properties of the joints.A large number of Fe-Ti,Ni-Ti brittle phases led to lots of longitudinal cracks in Ti3Al/GH536 joints and the average value of shear strength was 86.4MPa.

Effect of Post-Welded Annealing on Microstructure and Properties of Welding Joint for 5B70 Al-Mg-Sc Alloy Sheet

HE Zhen-bo, YIN Zhi-min, CHEN Ji-qiang

2010, 30(5): 39-43.

[Abstract](1671) [PDF 1256KB](417)

Abstract:
5B70 Al-Mg-Sc alloy sheets with 6 mm thickness at H32 heat treatment condition were welded using 5B71 Al-Mg-Sc welding wire and then the welded joints were annealed at 280～340℃ for 1h.The microstructures and mechanical properties of the welded joints at different condition were analyzed by tensile test,micro-hardness test,OM and TEM.The results show that the welding joints have apparent dendrite grain structure,while after post-welded annealing,the kind of dendrite grain structure disappeared.During post-welded annealing,large amounts of coherent Al3(Sc,Zr) particles precipitate and distribute uniformly within the matrix,which increase the strength of the welded joint.At the range of 280～340℃ annealing,the higher the annealing temperature,the higher the strength of the welded joints,and the elongation ratio of welded joints also increased.The Al3(Sc,Zr) strengthening precipitates should be responsible for the improvement of mechanical properties of the welded joints with post-welded annealing.

Effects of Cold Hole-expansion on Microstructure and Fatigue Property of 7055-T7751 Aluminum Alloy Plate

ZHANG Kun, GONG Peng, Song De-yu, RU Ji-gang

2010, 30(5): 44-48.

[Abstract](1687) [PDF 1315KB](300)

Abstract:
Cold hole-expansion processing was employed on the 7055-T7751 aluminum alloy plate using a mandrel.The effects of the processing on fatigue life and microstructures of 7055-T7751 specimens were analyzed by fatigue tests under cyclic loading.The fatigue striation spacing were measured by scanning electron microscopy.The residual stresses and dislocation introduced into the specimens due to cold hole-expansion were evaluated by X-ray diffraction and transmission electron microscopy.The results show that the 7055-T7751 aluminum alloy specimens were extremely strengthened by cold hole-expansion of 3-5% shrink and the maximum fatigue life was increased to 33 times of the non-cold-worked specimens.The strengthening layer depth was almost 7mm,and the maximum residual compressive stress of ? 554MPa was observed at a distance of 0.5mm to the border of the hole.The residual compressive stress and dislocation cell structure around the cold-worked holes retarded the fatigue crack growth rate in the initial and propagation stages,and then improved the whole fatigue life.

Erosion Resistance of Laser Remelted Al₂O₃-13% TiO₂ Composite Ceramic Coatings

WANG Dong-sheng, TIAN Zong-jun, DUAN Zong-yin, WANG Jing-wen, SHEN Li-da, HUANG Yin-hui

2010, 30(5): 49-53.

[Abstract](1635) [PDF 715KB](284)

Abstract:
In order to improve the erosion resistance of the Al2O3-13%TiO2 composite ceramic coatings fabricated by plasma spraying on TiAl alloy surface,laser remelting experiment was carried out and the effects of laser remelting on microstructure and erosion resistance on coatings were studied.Meanwhile,the erosion mechanisms of the ceramic coatings were discussed based on the experimental results.The results show that the laser-remelted coating exhibits a compact remelted zone which is composed of fine equiaxed grains.The laser-remelted coating has better erosion resistance than the plasma-sprayed coating and shows a brittleness erosion mechanism.During erosion process,cracking occurs within region near the surface of the laser-remelted ceramic coating and that erosion occurs by removal of these small blocks.

Microstructures and Properties of Ceramic Layer on 7A55 Aluminium Alloy by Micro-Arc Oxidation

LI Zhong-sheng, WU Hu-lin, PAN Fu-sheng, ZHANG Long-ping, HE Qing-bing

2010, 30(5): 54-57.

[Abstract](1568) [PDF 1033KB](250)

Abstract:
Ceramic oxide coatings were fabricated on 7A55 aluminium alloy surface by micro-arc oxidation(MAO) at the constant current density of 6A/dm2 in phosphate electrolyte.The Growth curves,microphotoes,element linear distributions,phase composition and adhesion to the substrate s of the micro-arc oxidation coatings were investigated.The results indicate that the thickness of ceramic coatings increases with increasing of oxidation time,while the growth rates are different during processing.The coating is only a layer and grows towards outer surface mainly.EDX analysis reveals that Al and O as the major constituents are distributed uniformly throughout the coating thickness.The coating is composed of α-Al2O3 and γ-Al2O3,while the γ-Al2O3 phase is high content.Micro-scratch test reveals that there is an excellent adhesion between coating and substrate.

Study on Films of Zinc Immersion on AZ91D Magnesium Alloy

QIAN Jian-gang, XU Min, TENG Xiao-ming, HUANG Wei

2010, 30(5): 58-62.

[Abstract](1638) [PDF 1097KB](318)

Abstract:
Magnesium alloy usually needs the process of zinc immersion before electrop lating or electroless plating.The corrosion resistance and the adhesion of the subsequent metalcoatings are directly influenced by the quality of the zinc mimersion.The traditional mimersion process usually needs hydrofluoric acid which is harmful to the environment.The influences of the main components and the parameters in the zinc mime rsion process which didntuse the hydro fluoricacidas the pre activation on the perform ance of the zinc coatings were investigated by cross cuttes,tneutral salt spray test and other tests.Results show that the concentration of the zinc sulfate and potassium pyropho sphate,the temperature,pH and the time greatly in fluence the quality of the zinc film.The main components and the parameters in the zinc mimersion process are as follows:zinc sulfate 40g/L,potassium py rophosphate 125g/L,inhibitor 20g/L,additive 80g/L,temperature 75±5℃,pH 10.5±0.5,tmie 2~3m in;An excellent adherent zinc alloy coating can be obtained by using the optimal process and the corrosion resistance tmie in neutral salt spray testis 28min.AZ91D Mgalloy is electrop lated with copper after using the zinc immersion process.The adhesion of the subsequent metal coatings and the corrosion resistance are both excellent

High Temperature Resistance of Al-Si Coating on DZ40M Superalloy

ZHANG Peng-fei, LI Jian-ping, LU Feng, CAI Yan

2010, 30(5): 63-66.

[Abstract](1521) [PDF 477KB](298)

Abstract:
The Al-Si coating on DZ40M superalloy was prepared by slurry process.The high temperature oxidation behaviors at 1000℃ and the hot corrosion behaviors at 900℃ were studied.The results indicate that the Al-Si coating has excellent high temperature oxidation resistance,the coating consists of CoAl phase,as the oxidation time extending,the degradation of CoAl phase take place,transform to α-Co phase gradually;both of the superalloy and coating have excellent hot corrosion resistance.

Impact on Fatigue Properties by Salty Spray of Bonded Composite Repair of Aluminum Substrates

WANG Yue-ran, XIAO Jia-yu, XIAO Xi-hai, ZENG Jing-cheng, JIANG Da-zhi, XING Su-li

2010, 30(5): 67-72.

[Abstract](1594) [PDF 1300KB](217)

Abstract:
Taking vacuum bag techniques for patches of carbon fiber/epoxy(Cf/epoxy) composites,this study tested the corrosion fatigue properties of bonded and non-bonded aluminum alloy plate with different time of salty spray.The fatigue life,critical crack length and constant C and m in the Paris law are investigated under different corrosion time.The results show that bonded Cf/epoxy patches repair increase fatigue life.After 1700h's corrosion,the fatigue life of non-bonded center-cracked aluminum alloy decreases by 53.8%,while the bonded ones only by 38.6%.The critical crack length turns longer after bonding.Along with the extending of corrosion,the critical crack dimension of bonded and non-bonded aluminum alloy change little.Both constant C and m in Paris law depress with the extending of corrosion.Paris law is suitable to predict the fatigue life and the behavior of crack-growth in the region of Paris,but the errors between prediction and experiment increase form 5%(0h) to 10%(1500h).

Effect of Pulsed Bias on Microstructure and Mechanical Properties of CrN_x Coatings Deposited by Arc Ion Plating

ZHANG Xiao-ning, CHEN Kang-min, ZHENG Chen-chao, HUAN Yan, GUAN Qing-feng, GONG Lei, SUN Chao

2010, 30(5): 73-77.

[Abstract](1649) [PDF 963KB](360)

Abstract:
CrNx coatings were deposited on the Ti-6Al-4V substrate by arc ion plating process.The effects of pulse bias voltage on the microstructure and some mechanical properties of thin films were studied.The results show that the number and the size of macroparticles decrease significantly when the pulsed bias increases within a certain range,and the surface flatness is improved greatly.Simultaneously,the phases of CrNx are changed CrN phase into CrN phase along with the bcc-Cr and hcp-Cr2N with increasing negative substrate bias.The hardness and the adhesion of CrNx coatings could reach 2479kg/mm2 and 43N.The coefficient of friction of CrNx coatings achieves its minimum 0.43 at a pulsed bias of-300V.

Frication and Wear Mechanism of BaSO₄/PTFE Composites under Dry Conditions

YAN Lü-ke, LI Wei-guang, Kou Kai-chang, SUN Zeng-zhi, XU Ou-min

2010, 30(5): 78-81.

[Abstract](1646) [PDF 855KB](377)

Abstract:
BaSO4/PTFE composites were prepared using barium sulfate(BaSO4) particles filling polytetrafluoroethylene(PTFE) by high speed mechanically mixture,cold moulding and sintering in the air.The tribological properties of the composites were evaluated on an M-200 tester under dry sliding condition.The effects of BaSO4 amount on the friction and wear properties of the BaSO4/PTFE composites were investigated.The results showed that,the wear resistance of PTFE was improved by filling BaSO4 particles remarkably,30%BaSO4/70%PTFE composites' was increased two orders of magnitude compared to neat PTFE.And the worn surface morphologies of composites were characterized and analyzed by scanning electron microscope.The results indicated that,the friction and wear mechanism of the BaSO4/PTFE composites was changed from the adhesive wear to the abrasive wear and the fatigue wear with increasing amount of BaSO4.

Joint Properties of 2D/3D Basalt Fabric Reinforced Composites

KE Qian-lan, YAO Lan, ZHU Tian-gang, ZHOU Dong-chun, DENG Tian-ming, QIU Yi-ping

2010, 30(5): 82-87.

[Abstract](1450) [PDF 707KB](233)

Abstract:
The joint properties of 2D and 3D basalt fiber reinforced composites were investigated in this paper.The reinforcement of the joint composites was fabricated on the 3D orthogonal weaving machine.The single and double ladder 3D basalt fabric were both designed and woven by adjusting the weaving method.Two types of lap methods of single-face lap and double-face lap were applied in the joint processing,and four lap lengths were chosen.The final composites were obtained by using vaccum assistant resin transfer molding technology.The tensile and bending properties of the two types of lap composites were compared respectively.The results showed that the double-face lap composites had better mechanical properties than the single-face ones.

Experimental Study on Low Cycle Fatigue of Directionally Solidified Superalloy DZ125 with Different Holding Time

LIU Jin-long, YANG Xiao-guang, SHI Duo-qi, WANG Jing-ke

2010, 30(5): 88-92.

[Abstract](1747) [PDF 871KB](338)

Abstract:
Low cycle fatigue(LCF) tests of directionally solidified superalloy DZ125 were conducted with different holding time at 850℃.The tensile holding time of experiment was 1s,60s,120s and 240s.Analysis of cyclic stress-strain,strain response,fatigue life,micro-fracture was carried out.The results indicated that holding time had significant effect to low cycle fatigue behavior.With the increase of holding time,the fatigue life decreased,but when the holding time exceeded a value,the fatigue life had the trend of becoming stable.In addition,creep damage played more important role as holding time increased.

Effect of Phase Angle on High-cycle Fatigue Failure of 2A12-T4 Aluminum Alloy under Tension-torsion Non-proportional Loading

SHI Xin-hong, ZHANG Jian-yu, BAO Rui, FEI Bin-jun

2010, 30(5): 93-96.

[Abstract](1650) [PDF 1364KB](216)

Abstract:
Fatigue experiments were carried out to investigate the effect of phase angle on multi-axial high-cycle fatigue failure of 2A12-T4 aluminum alloy under tension-torsion non-proportional loading.The change of fatigue life with phase angle under different ratio of stress amplitude was discussed.The failure mode of specimen was studied under different phase angle when τa/σa=1based on macro-analysis of fracture.The results showed that when ratio of stress amplitude τa/σa=1,fatigue life raised gradually with the increasing of phase angle and had an exponential relation with the sin of phase angle under the same Von-Mises equivalent stress.When phase angle increased,fatigue life raised under different ratio of stress amplitude and the change was more obvious when τa/σa=1 than others.By analysis,fracture presented a mixed mode of modelⅠand modelⅡ.The dominant mode had a transition from modelⅠto modelⅡwhen phase angle increased.

2010 Vol. 30, No. 5