航空材料学报

Electromagnetic Field of Continuous Melting and Directional Solidification of Ti Alloys in Cold Crucible

WANG Yan-li, GUO Jing-jie, FU Heng-zhi

2010, 30(1): 1-5.

[Abstract](1525) [PDF 626KB](257)

Abstract:
A model with a near rectangular cold crucible system was based by applying ANSYS software.The magnetic intensity distributions inside the crucible were simulated during cold crucible continuous melting and directional solidification.The effects of titanium alloys and in put current on the magnetic intensity distributions in the crucible were analyzed.It is found that adding titanium alloys doesn't affect the axial magnetic intensity distributions inside the crucible.The distributions of magnetic field are non-uniform across the defined calculation region.The magnetic field mainly acts on the slit area of the crucible,especially the density of electromagnetic force of the area surrounded by the coil and the crucible apparently higher than other positions.After the Ti6Al4V ingots are placed in the cold crucible,the original lines of magnetic force of hollow area in the crucible turns to concentrate on the surface of the ingots and aggregates in the region of ingot's melting and melt hump's electromagnetic confinement shaping.And the increase of input current causes the increase of magnetic intensity.

Influence of Cooling Rate on Phase Transformation of TC21 Alloy

WANG Yi-hong, KOU Hong-chao, ZHU Zhi-shou, CHANG Hui, ZHOU Lian, LI Jin-shan

2010, 30(1): 6-10.

[Abstract](1525) [PDF 710KB](265)

Abstract:
The effects of cooling rates from elevated temperature on phase transformations in TC21 alloy were investigated by using end quenching.Samples from different regions(cooling rates) were analyzed by using optical micrograph(0M),Xray diffractometry(XRD),transmission electron microscopy(TEM),and Vickers microhardness.The results show that cooling rates above 122℃/s result in a martensitic transformation,a massive transformation being observed between 122 and 3°C/s,this ransformation being gradually replaced by diffusion controlled Widmanst?tten α formation with decreasing cooling rate.These α layers was of two types,type 1 having a smoother appearance,type 2 having a zig-zagged appearance.With the cooling rates decreasing,the microhardness of TC21 alloy decreased after increased.When the cooling rates was smaller than 8℃/s,the microhardness of TC21 alloy decreased dramatically.

Microstructural Evolution of Near-α Titanium Alloy during Long-Term High Temperature Exposure and its Influence on Thermal Stability

CAI Jian-ming, HUANG Xu, CAO Chun-xiao, MA Ji-min

2010, 30(1): 11-18.

[Abstract](1611) [PDF 2713KB](246)

Abstract:
Microstructural evolution of a near-α titanium alloy TG6 disc forging processed in α+β phase field during long-term high temperature exposure and its influence on the thermal stability were studied.The results show that the room temperature tensile strength increased about 5% and the ductility reduced remarkably lower than 50% after 600℃/100h or 300h exposed for TG6 titanium alloy,and the fracture surface has a tendency of flat,terrace-like steps and secondary crack which showed an obvious cleavage fracture characteristic.During long-term exposure under 600℃ environment,the microstructural change is precipitation of the coherent ordered α2 phase and silicide.The microstructure and the tensile properties tend to be stable with increasing the exposure time.The precipitation of α2 phase is the main reason for the great loss of ductility during high temperature long-term exposure because the precipitated α2 may promote planar slip and inhomogeneous deformation while tensile deformation.The precipitation of silicide may promote the intensity of slip and is the minor reason for the ductility loss.

Study on Fabrication and Mechanical Properties of Powder Hot Extruded Al+Zn-Mg-Cu Alby

WANG Shao-qing, YU Hua-shun, ZHAO Qi, ZHANG Zhen-ya, MIN Guang-hui

2010, 30(1): 19-25.

[Abstract](1527) [PDF 1182KB](267)

Abstract:
In this study,an Al+Zn-Mg-Cu ultra strength aluminium alloy was fabricated by powder hot extrusion process,and the effects of powder granularity and extrusion ratio on microstructures and mechanical properties of alloys were investigated.The results show that the optimal powder median size(D50) for the consolidation of alloyed powder is 28.38μm,and the extrusion ratio(λ) is 25.By extrusion at 400℃,the best mechanical properties were obtained with the above as-optimized processing parameters.After T6 temper,i.e.460℃×2.5h water quenching+120℃×24h air cooling,the tensile strength,yield strength and elongation of the heat treated alloy are 731MPa,670MPa and 6.2%,respectively.The mechanical properties of extruded alloys increasing with the decrease of powder granularity are due to grain refinement.The mechanical properties of extruded alloys increase with the increase of extrusion ratio from 9 to 25.Coarse MgZn2 precipitated phases and complete dynamic recrystallization lead to the reducing of mechanical properties of the extruded alloy produced by extrusion ratio 36.

Study on Surface Heat Transfer Coefficients of FGH96 P/M Superalloy Disk during Heat-Treatment Process

ZHANG Jia-feng, ZOU Jin-wen, KANG Jin-wu, LIU Bai-cheng

2010, 30(1): 26-29.

[Abstract](1509) [PDF 413KB](263)

Abstract:
Heat extraction behaviors of a FGH96 P/M superalloy disk under static air cooling,forced air cooling and oil quenching conditions were studied by experiments and the surface heat transfer coefficients were obtained by solving the inverse thermal problems.Numerical simulation of the heat-treatment process of a real disk was then carried out.The results showed that the heat extraction rates of oil quenching were much higher than those in the other two conditions,and the peak value was almost 10 times of that in the static air cooling.The heat-treatment process was appropriate as the stress generated in the quenching process was lower than the yield strength of the disk material.

Process of 316L stainless steel Coarse Powder by Injection Molding

QIAO Bin, SHANG Feng, DING Mei, LI Hua-qiang, HE Yi-qiang, YANG Jian-ming

2010, 30(1): 30-35.

[Abstract](1658) [PDF 1162KB](368)

Abstract:
316L stainless steel by injection molding using coarser powder with particle size of 30um was studied.The effect of injection parameters to the quality of green was studied by orthogonal arrays design and statistical analysis method according to the density and strength of the green part.The right debinding and sintering processes were got.The sintered part is provided with the ideal mechanical property,tensile strength is 630MPa,yield strength is 280MPa,elongation is 52%,hardness is 69.5HRB,corrosion resisting property was evaluated.

High Temperature Deformation Behavior of Fine-Grained AZ31 Magnesium Alloy

HU Yan-hui, LI Jian-guo, TAN Dun-qiang, CAO Cou-xian

2010, 30(1): 36-40.

[Abstract](1604) [PDF 1737KB](542)

Abstract:
Unidirectional hot compressive tests of AZ31 magnesium alloy after grain refinement were performed by Gleeble-1500 machine at strain rates changed among 0.01~1s-1 and deformation temperature varied among 300~450℃.Each parameter of the constitutive equation was gained by analyzing and calculating the results of samples,and a complete constitutive equation of AZ31 magnesium alloy for high temperature was fabricated,furthermore,the microstructures of compressive samples were studied.The results show that the hot deformation activation energy Q is 177.181 kJ/mol and the stress exponent n is 6.24.Compared with the edge of the compressive samples,the center has more intense degeneration.With the temperature increasing,obvious recrystallization is observed in the compressive organization.The new grain forms toward the crystal boundary and then grows up.

Study on Friction Plug Welding of 2014 Aluminum Alloy FSW Joint

ZHAO Yan-hua, LIU Jing-duo, ZHANG Li-na, SUN Zhong-shao, WANG Guo-qing

2010, 30(1): 41-46.

[Abstract](1517) [PDF 1554KB](282)

Abstract:
Friction plug welding of 2014 Al alloy FSW joints in 4 mm thickness have been successfully completed.The metallurgy experiment demonstrates that the FPW joint microstructures could be divided into three different regions:welding line zone,HAZ and base metal zone.The dynamic recrystallization occurs in the welding line zone,which consist of refined,equiaxed grains.Mechanical property measurements demonstrate that the peak tensile strength of the joint can reach more than 330MPa,reach or exceed the joint strength of the FSW welding joint when the suited parameters were used.The microhardness analysis shows that the hardness of the welding line zone is higher than the other zones,but the changes of the FPW joint microhardness is not very acutely.

Strengthing Mechanism of in-situ Synthesized Particles in Friction Stir Processed Aluminum Alloy

WEI Yan-ni, LI Jing-long, XIONG Jiang-tao, ZHANG Fu-sheng, QIAN Jin-wen, LI Xue-fei

2010, 30(1): 47-51.

[Abstract](1403) [PDF 421KB](306)

Abstract:
Friction stir processing(FSP) was conducted by using aluminum alloy plate 1100-H14.Prior to stiring,a rectangular groove was machined on the plate along the center of stir pass,in which nickel powder was filled.Via in-situ synthesis during the processing thermal cycle,Ni particles in Al base metal would react with Al to form hard particles of NiAl intermetallics.Thus,a composite layer would be fabricated.The results show that Ni particles were stir-crushed to pieces and NiAl3 reactive particles,in submicron size,were formed.A portion of NiAl3 particles were further refined by stir-crushing.The microhardness test shows evident increase of the hardness distributions in the composite layer.Compared with ceramic powders added in FSP,physical models were proposed to describe both particle-strengthing mechanisms.In-situ synthesesed intermetallic particles have the crystal boundaries to base metal with strong metallic bonds(twinned crystal boundary,for example),which makes difficulty for dislocatons to pass around that forms crystal boundary strengthing mechanism,whereas the stir-crush refined particles issue fine particle dispersive strengthing mechanism.However,in the friction stir processing by adding hard ceramics particles,much weak bonds between particles and base metal contributes little material strengthing as dislocations may easily pass around.

Study on Fatigue Crack Propagation in Different Zones of TA15 Electron Beam Welded Joint

LI Xing-zhi, HU Shu-bing, XIAO Jian-zhong, WANG Ya-jun, LI Qing-hua, JI Long-bo

2010, 30(1): 52-56.

[Abstract](1489) [PDF 733KB](396)

Abstract:
The microstructure,hardness,fatigue crack propagation and fatigue fractograph in the fusion zone(FZ) and heat affection zone(HAZ) of TA15 electron beam welded(EBW) joint were studied in this paper.The results indicate that the microstructure in FZ is characterized by bulky aciculate martensite,and in HAZ,the microstructure is composed of α'martensite+lamellar α and β.That is,it shows a transition from FZ to base material(BM).The hardness of FZ is largest,that of BM is the lowest,and HAZ with between them.The fatigue crack propagation rate is closely relative with their microstructure.The HAZ containing more plastic lamellar α exhibits a better resistance to the fatigue crack propagation than FZ.

Structure and Oxidation Behavior of ZrN Diffusion Barrier Prepared by Arc Ion Plating

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

2010, 30(1): 57-61.

[Abstract](1490) [PDF 1101KB](172)

Abstract:
Al has been deposited between HY3(NiCrAlYSi)coating and K5 Nickel super-alloy substrate as a diffusion barrier layer by ARC ion plating(AIP)technology.The inhibition effects of diffusion barrier layer on the interdiffusion of the alloy elements and coating system were studied.The influences of the barrier layer on the oxidation kinetics were also investigated.The tests of coating for high-temperature oxidation resistance were conducted.The coatings were characterized by scanning electron microscopy and X-ray diffraction.The results indicated that the Al2O3 layer inhibited the inter-diffusion between the coating and the substrate,thus the Al2O3 layer could improved the high temperature oxidation resistance of HY3 coatings and K5 super-alby.

Corrosion Behavior of Magnesium Alloys AZ91D in NaCl Solution

BAI Li-qun, SHU Kang-ying, LI Di

2010, 30(1): 62-66.

[Abstract](1604) [PDF 1175KB](416)

Abstract:
Magnesium alloys have been used wide applications for their excellent properties.the corrosion and electrochemical behaviors of casting and die-casting Mg alloys AZ91D in 5% NaCl solution were investigated.The quantity of H2 gas evolution and mass loss were measured and both showed that the corrosion resistance of die-casting AZ91D was higher than that of casting AZ91D.This result was further proved by EIS and the difference of corrosion resistance between these two materials was also explained by monitoring Rt and Y during immersion time.Whatever Mg alloys,major corrosion products were composed of 'nubbly' compound [Mg(OH)2] and pine 'needle' compound [Mg2Cl(OH)3·4H2O].

Effect of Neutral Salt Spray Precorrosion on Fatigue Life of AF1410 Steel

HAO Xue-long, LIU Jian-hua, LI Song-mei, YU Mei, WANG Zong-wu

2010, 30(1): 67-71.

[Abstract](1563) [PDF 892KB](410)

Abstract:
The corrosion resistance of AF1410 steel in the neutral salt spray environment was studied using the methods of weight loss and XRD.After different precorrosion time in the neutral salt spray,the fatigue properties of the specimens were tested,and the influences of the different precorrosion time on the fatigue life of the material were investigated.The results showed that serious all-around corrosion happened on the AF1410 steel,and the corrosion products are mainly FeO(OH) and Fe3O.The corrosion weight loss curve was plotted,and the fatigue fracture morphology was observed.It was shown that with the increasing of the corrosion time,the degree of the corrosion damage increased and more fatigue crack initiations were apt to take shape,which led to the final fatigue rupture.Finally,the fatigue life properties of AF1410 steel after neutral salt spray corrosion were obtained and the influence coefficient C(t) of the pre-corrosion on the fatigue life was plotted.

Test Research on Low-Cycle Fatigue Damage of Parts by Metal Magnetic Memory Methods

LIU Chang-kui, CHEN Xing, ZHANG Bing, REN Ji-lin, DONG Shi-yun, TAO Chun-hu

2010, 30(1): 72-77.

[Abstract](1532) [PDF 830KB](339)

Abstract:
Low-cycle fatigue tests of notched 18CrNi4A steel specimens were carried out under three different fatigue stresses,and metal magnetic memory(MMM) signals were detected.The effects of stress concentration,fatigue damage and fatigue stress on the MMM signals were investigated.The results show that fatigue-damaged locations can be predicated effectively according to the mutational characters of the MMM signal Hp(y) curve and K curve.It is found that the zero-crossing points of the MMM signal H'p(y) curve(H'p(y)=Hp(y)N-Hp(y)0) have the same positions as the fracture points,so it can be concluded that fatigue-damaged locations can be predicated more effectively by zero-crossing points.The absolute value of the MMM signal feature parameter Kmax increases with the aggravation of the fatigue damage.The fatigue damage can be assessed effectively by the value of Kmax.In addition,there is an inherent relationship between the fatigue stress and the MMM signal feature parameters Hp(y)max ,Hp(y)min and Hp(y)sub;the larger the fatigue stress is,the larger the absolute values of the feature parameters are.

Comparison of Tensile Behavior of Plain-Woven Carbon/Silicon Carbide Composites at Room Temperature and High Temperature

WANG Kun, CHEN Liu-ding, ZHENG Xiang

2010, 30(1): 78-84.

[Abstract](1455) [PDF 976KB](293)

Abstract:
Monotonic tensile experiments at room temperature and 1300℃ were performed to investigate the macro-mechanical behavior of plain-woven C/SiC ceramic matrix composites(CMCs) produced with CVI technique.Two environments including inert atmosphere and wet oxygen atmosphere were simulated at 1300℃.The microstructure of specimens were observed by optical microscope and scanning electron microscope to analyse its damage mechanism.The results indicate that,the responses of C/SiC composite under tensile loading at both room temperature and 1300℃ are nonlinear to rupture and damage appears at very low stress level.The tensile strength and failure strain at room temperature are lower than at 1300℃ in inert atmosphere but higher than at 1300℃ in wet oxygen atmosphere,respectively.The main reason of the former is the decrease of interfacial sliding resistance at 1300℃ in inert atmosphere.The main reason of the latter is fiber oxidation at 1300℃ in wet oxygen atmosphere.The tensile specimens all break in a ductile manner.Fractography analysis shows that the fracture surfaces are almost the same in the three environments except the obviously oxidative trace in wet oxygen atmosphere.The specimens in inert atmosphere have the longest pull-out length of fiber.Matrix cracks around the 0° fiber bundles,interlaminar cracks,fracture and pullout of 0° fiber and 0° bundles along with the pullout of 90°bundles are the main damage mechanisms.

Modeling of Electrical Resistance Influence in Carbon/Epoxy Composites Result from Drilling and Impact

XIE Xiao-lin, QUAN Hong-ying, LI Zhi-peng, WANG Gao-chao, Zhang Jian-chao

2010, 30(1): 85-89.

[Abstract](1425) [PDF 919KB](220)

Abstract:
Electrical resistance of carbon /epoxy composites were measured before and after they were drilled or impacted separately,the mechanism of electrical resistance change in composites were analyzed,the calculating model of resistance influence in composites were established.The results show that electrical resistance of composites was changed after they had been drilled or impacted,it can be ascribed to the change of contact point among carbon fibers(sectional region of electrical current)and charge conducting route in composites.Impact calculating model derivate from drilling model can greatly simplify the calculating of influence from impact on electrical resistance in composites.According to the modeling of electrical resistance influence in carbon /epoxy composites resulting from drilling and impact,the fractional change in resistance of composites can be calculated,and they coincided with the experimental results.

Studies on Mechanical Properties of Polyurethane Elastomer with Low Smoke Ablation-Resistant

ZHOU Yan-ming, GAO Jian-feng, SUN Zhong-zhan, YIN Wei-feng

2010, 30(1): 90-94.

[Abstract](1560) [PDF 874KB](333)

Abstract:
The polyurethane elastomer was prepared through the reaction of HDI,PPG and MOCA.And then,the functional filler with smoke suppression and anti-ablation material was doped in to the polyurethane elastomer.The effect of the soft segment length and the crosslinked degree on the mechanical properties of the polyurethane elastomer was investigated in detail.The tensile strength、shore hardness and Spring back rate of the polyurethane elastomer decreased with the increase in the soft segment length.However,the elongation at break increased.At the same time,the results showed that the breaking elongation and shore hardness decreased,and the spring back rate increased with the incrensement of the crosslinked degree.In addition,the polyurethane elastomer containing functional filler has low-smoke and ablation-resistance.

2010 Vol. 30, No. 1