航空材料学报

Research on Effect of Laser Remelting on Properties of Jet Electrodeposited Nanocrystalline Nickel Coatings

WANG Dong-sheng, HUANG Yin-hui, TIAN Zong-jun, LIU Zhi-dong, ZHU Jun

2008, 28(3): 1-4.

[Abstract](1199) [PDF 890KB](220)

Abstract:
The nanocrystalline nickel coatings were prepared by jet electrodepositing on the substrate of 0.45% carbon steel,the effects of laser remelting on the properties of coatings were investigated.The surface morphology and the grain size of coating were analyzed by SEM and XRD,and the microhardness and corrosion resistance of coatings were also tested.The results show that the nickel coatings prepared by jet electrodepositing own a fine-grained structure(average grain size is 13.7 nm)with a smooth surface and high density under the optimum processing parameters.However,there are still some pores and other defects.After laser remelting,the grain size of coating is greatly reduced,the density of coating is also improved and the bonding state between the coating and substrate changes from mechanical combination to metallurgical combination.So the laser remelted specimen has higher hardness,better corrosion resistance than ad-deposited coating.

Effects of Long-Term Air Exposure on Microstructures and Mechanical Properties for W+Nb Containing Lamellar TiAl Alloys

CONG Tao, HUANG Ze-wen

2008, 28(3): 5-11.

[Abstract](1289) [PDF 854KB](188)

Abstract:
The effects of long-term exposure to 700℃ air on the microstructures of W+Nb containing TiAl alloy,obtained through different hot isostatic pressing treatments,were investigated.It was found that decomposition of metastable α2 lamellae occurred along the α2/γ boundary direction,which was in fact the phase transformation of α2→α2+γ.A small amount of α2+γ→B2+ω phase transformation was observed in the decomposing α2+γ lamellae packets at later exposure stage.Also found was Oswald coarsening of ω particles in retained B2+ω blocks during the 10000-hour long thermal exposure process,during which some of B2 was still retained.No significant changes in mechanical properties were produced throughout the 10000-hour air exposure process.This indicates that the W+Nb containing TiAl alloy is relatively stable in terms of its resistance against thermal deterioration.

Influence of Fe and Nb Addition on Two-Way Shape Memory Effect of TiNi Shape Memory Alloy Rings

YAN Ying, JIN Wei, CAO Ming-zhou

2008, 28(3): 12-15.

[Abstract](1238) [PDF 836KB](262)

Abstract:
The influence of pre-strains and number of thermal cycling on the two-way shape memory strains of TiNi,TiNiFe and TiNiNb alloy rings were investigated to provide theoretical basis for their applications in engineering.The results indicate that the two-way memory strains of TiNi alloy rings deformed at temperature less than Mf point increase with the increase of thermal cycling number within the range of 10.4%~13.8% pre-strains.The maximum two-way memory strain of 4.15% is obtained at pre-strain of 13.8% and thermal cycling number up to 4.And when Fe or Nb atoms are added to TiNi alloys,the two-way memory strains of alloy rings first increase and then decrease at the ranges of 10.71%~15.18% pre-strains,their maximums are 3.14% and 2.56%,respectively.At the same pre-strain and thermal cycling number,the two-way memory strains of TiNi alloy rings are the greatest,after pre-strain and cycling number are more than 12.50% and 2,the two-way memory strains of TiNiFe rings rapidly rise and are greater than that of TiNiNb alloy rings.

Synthesis of Heat Resistant Intermetallic Matrix Composites on Steel Surface Through Thermal Explosion

GAO Ming-juan, WANG Shu-qi, YANG Zi-run, CHEN Kang-min, CUI Xiang-hong, WEI Min-xian

2008, 28(3): 16-19.

[Abstract](1192) [PDF 682KB](163)

Abstract:
A layer of intermetallic compound matrix surface composite was fabricated through thermal explosion reaction of Ti-C-3Ni-Al system initiated by steel melt.The thermal dynamics and morphology of products in thermal explosion of Ti-C-3Ni-Al were analyzed.The phases,and microstructure of the composite as well as interface bond with steel were studied.The results show that the reaction of Ti-C-3Ni-Al is completed in liquid steel during poring to form TiC particulate reinforced intermetallic compound matrix surface composite on steel.TiC content is found to influence apparently the microstructure and the interface bond of the composite.With increase of TiC,the composite turns to be compact and have slightly larger TiC particulates.The metallurgical bonding of interface between the composite and steel is established.

Effects of HIP Temperature on Microstructures of a New P/M Superalloy

JIA Jian, TAO Yu, ZHANG Yi-wen, ZHANG Ying

2008, 28(3): 20-23.

[Abstract](1179) [PDF 1381KB](383)

Abstract:
The HIPed microstructures of a new P/M superalloy under different temperatures are studied.The effects of HIP temperature on the grain size,prior particle boundary,remained dendrites and γ' in the HIPed alloy ingot are described.The results of present study indicate that at a HIP temperature of 1140℃,the alloy showed an incompletely recrystalized microstructure with clear residual dendrites and PPB,gamma prime precipitates were distributed unevenly and varied in size and shape;At a HIP temperature of 1180℃,the alloy showed a uniformly recrystalized microstructure without residual dendrites and PPB basically,gamma prime precipitates were distributed quite evenly,mainly existed as butterfly-shape within grains and long strip-shape in grain boundaries.

Effect of Furnace Cooling after Hot Iso-static Pressing on Microstructure and Mechanical Properties of Cast Superalloy K488

LIU Xiao-gong, RAO Yang, XIAO Cheng-bo, TANG Ding-zhong

2008, 28(3): 24-27.

[Abstract](1209) [PDF 1634KB](602)

Abstract:
The effect of different heat treatment processing including hot iso-static pressing(HIP)on microstructure,high temperature tensile and stress-rupture properties of superalloy K488 was investigated.The results show that the tensile and stress-rupture properties at 900℃ of specimens through furnace cooling after HIP(1180℃/150MPa/4h)decrease compared with the properties of as-cast specimens,which is due to the irregular and decreasing volume percentage of γ' in dendritic areas and the remained γ-γ' eutectic phases in interdentritic areas.The properties of the HIPed specimens can be improved by standard heat treatment(1170℃/4.5h+1050℃/4.5h+850℃/16h)because that irregular γ' phases in dendritic area are returned to be cubic and in homogeneous distribution,the γ-γ' eutectic phases in interdentritic areas disappear.The best properties among the different processing can be achieved by standard heat treatment,during which the finest γ' phases can be precipitated homogeneously in dendritic areas.

Microstructure of IC10 Superalloy

ZHAO Xi-hong, HUANG Zhao-hui, TAN Yong-ning, ZHANG Qiang, JIA Xin-yun, XU Hui-bin

2008, 28(3): 28-33.

[Abstract](1267) [PDF 2367KB](307)

Abstract:
The microstructures of cast IC10 superalloy are composed of γ',γ,γ+γ' eutectics and MC carbides.The volume fraction of γ' phase is 64 percent,and the MC phase are mainly TaC and HfC,existing in form of spot,Chinese script and blocky.The eutectics show sunflower shape,and γ' phase spheroidization occurs during the heat treatment.The carbides decompose and wrapps up γ'.After heat treatment there still exist some residual γ+γ' eutectics.At the grain boundary Hf-rich MC2 is precipitated.It is found that no harmful TCP phase forms even after aging for 3000 h at 950℃.The microstructural evolution during the aging treatment is characterized by γ' coarsing and fine HfC precipitation in the inerdendritic area,as well as precipitation of M23C6 and M6C phases in small volume along the grain boundary.

Research on Low Temperature and High Strain Rate Superplasticity of ZrO₂/Ni Nanocomposite Produced by Electrodeposition

DING Shui, ZHANG Kai-feng, WANG Guo-feng

2008, 28(3): 34-38.

[Abstract](1136) [PDF 1507KB](190)

Abstract:
Superplasticity of ZrO2/ Ni nanocomposite with a mean grain size of 45nm produced by pulse electrodeposition was investigated under the tensile test and bulging test.The elongation values obtained by tensile test at temperatures ranging from 420℃ to 500℃ and strain rates ranging from 8.33×10-4s-1 to 1.67×10-2s-1 are larger than 200%.A maximum elongation of 605% was obtained at a temperature of 450℃ and a strain rate of 1.67×10-3s-1.SEM was used to observe the microstructures of the samples before and after tensile test.The results indicate that grain growth occurs obviously by the effect of temperature.Superplastic bulging tests were subsequently performed using dies with diameters of 5mm.The values of H/d exceed 0.5 at temperatures ranging from 420℃ to 500℃,indicating the good superplasticity of ZrO2/ Ni nanocomposite.

Effects of Presintering on Properties of Reaction-Bonded Porous Silicon Nitride Ceramics

XU Jie, LUO Fa, ZHU Dong-mei, ZHOU Wan-cheng

2008, 28(3): 39-43.

[Abstract](1262) [PDF 1769KB](269)

Abstract:
This paper presents the dielectric and mechanical properties of porous silicon nitride ceramics.Silicon powders were mixed with pore-forming agent of 30wt% and agglomerant(PVA)of 1wt% and shaped into discs of Φ70 mm×5 mm by mould pressing under pressure of 40 Mpa.After volatilization of pore-forming agent at 200℃,the green bodies were subjected to presinter at different temperature for different holding time and then sintered at a maximum nitridation temperature of 1380℃ for 28 h in a home-made furnace in a flowing gas mixture of 95% N2/5% H2 under a positive pressure of 0.1 MPa.The heating-up rate is 3℃/min.The experimental results demonstrate that the dielectric constant ε',the dielectric loss tanδ increase diminutively but the bending strength of the samples increase evidently with increase of temperature and holding time of presintering.The dielectric constant ε' of porous silicon nitride ceramics with 5wt%Y2O3 and 5wt%Al2O3 presintered in vacuum atmosphere at 1200℃ for different holding time before sintered in a home-made furnace with same sintering technology reduce evidently with increase of holding time of presintering.

Preparation and Investigation on Microstructure and Properties of Ultra-fine Grained Laves Phase NbCr₂ Particulate Reinforced Nb Matrix Composites

XIAO Xuan, LU Shi-qiang, HU Ping, HUANG Ming-gang, LI Xin

2008, 28(3): 44-48.

[Abstract](1202) [PDF 395KB](196)

Abstract:
Laves phase NbCr2 reinforced Nb matrix composites were prepared by mechanical alloying followed by hot pressing.Microstructure and properties were investigated on Nb/NbCr2 composites prepared from 30h mechanically alloyed powders of elemental chromium and niobium powders with the Nb:Cr=77.5:22.5 atom ratio by hot pressing at 1250℃ for 10min,20min and 30min.The results indicate that Nb/NbCr2 composites with high relative density and homogeneous microstructure are obtained for three hot pressing time.The near equiaxed Laves phase NbCr2 granules with the volume fraction of 30% are distributed dispersedly in Nb solid solution matrix.The sample hot pressed for 20min has the optimum microstructure and properties,the grain sizes of Laves phase NbCr2 reach the sub-micron level,the sample has a relative density of 99.2%,Vickers hardness of 9.41GPa,yield strength of 2950MPa,compress strength of 3345MPa and strain of 7.01%.The effect of both Laves phase NbCr2 particulate reinforcement and fine grain strengthening and toughening has been fully realized.

Solidification Kinetics Of Alumina Suspension By Gel-Casting

TONG Jian-feng, CHEN Da-ming, LI Bao-wei, HUANG Hao

2008, 28(3): 49-52.

[Abstract](1158) [PDF 485KB](177)

Abstract:
Gel-casting is a novel net-shape method for forming ceramic green bodies,which is based on the principle of the in situ coagulation of a powder suspension via a reaction-rate-controlled macromolecule polymerized reaction after casting.The coagulation kinetics of alumina suspension for gel-casting forming were investigated through noting the change of temperature during gelling.The experimental results indicate that the coagulation kinetics can be successfully studied by the dynamic relaxation experiments intrems of "coagulation time",which provide a convenient and practicable way to research the coagulation kinetics of ceramic suspension.After optimizing the processing conditions of the alumina nitride suspension for gel-casting forming,a green body with uniform,narrow and unimodal pore size distribution was prepared.

Investigation of Novel Flame-Retardant Shell Compound Materials Use for Filling Microwave Absorbing Materials

YANG Wei-wei, LIU Shun-hua, DUAN Yu-ping

2008, 28(3): 53-56.

[Abstract](1188) [PDF 892KB](188)

Abstract:
In order to improve the flame-retardant of shell of the absorption materials.A novel compound shell material(CSM)which based on the fiber-glass was synthesized.In the same time,the rectangular shell were prepared by polypropylene cored slab(PCS).The reflection loss(RL)of CSM and PCS were measured using a reflection method in a range from 2 to 18 GHz.The result indicated that containing CSM composite material exhibited good absorption property at low frequency compared to PCS.Whereas,the RL of the composite material was decreased at high frequency.

Investigation on Effects of Processing Parameters on Infiltration of Composite RFI

TANG Bang-ming, LIANG Zi-qing, AN Xue-feng, LI Yan-liang, ZHANG Ming, YI Xiao-su

2008, 28(3): 57-61.

[Abstract](1175) [PDF 1347KB](216)

Abstract:
In this paper experimental processes are carried on to investigate the effects of resin viscosity and pressure on infiltrated heights and qualities of RFI composites.The results show that totally a higher viscosity will decrease the height of infiltration.Depending upon the resins of various viscosities and pretreatment of fabrics,the pressure leads two different effects on driving pressure of resin infusion and the compaction of fiber bed to decrease its permeability.Higher pressure always improves the quality of infiltration and lower void content.Analysis also shows that actually the influence of pressure on infiltration height is the results of cooperation of infiltrate pressure and compaction of fiber bed.

Hot-Work Processes Affect on Mechanical Properties and Weldability of Ti₃Al Based Alloy

LIU Wei-hong, CAO Chun-xiao, LI Yan, MAO Wei, LI Xiao-hong

2008, 28(3): 62-65.

[Abstract](1116) [PDF 497KB](198)

Abstract:
The microstructures and mechanical properties of Ti-24Al-15Nb-1Mo alloy under different hot-work processes(forging,hot-rolling and solution treatment)and weldability by tungsten inert gas(TIG)welding of the alloy have been investigated.The experimental results show that,compared with solution treatment,the different hot-work processes affect on the microstructures and mechanical properties of the alloy more markedly.Under forging condition this alloy has lower cold-crack susceptibility and higher mechanical properties of the joint.Decreasing constrain degree of joint,controlling post-welding cooling rate and carrying out post-welding heat treatment in time may be important ways to prevent cold-crack of the joint.

Microstructure and Mechanical Properties of K640 TLP Bonded Joint

ZHANG Lei, HOU Jin-bao, WEI You-hui

2008, 28(3): 66-70.

[Abstract](1289) [PDF 730KB](266)

Abstract:
In order to study the applicability of Transient Liquid Phase(TLP)bonding method to Cobalt-based superalloy K640,the bonding test adopting amorphous interlayer was carried out.Microstructure observation and mechanical property testing of joints,as well as fracture surface analysis were conducted after the test.The test results confirmed that the adoption of TLP method contributed to a satisfying jointing with perfect tightness and uniformity.The joint had homogeneous composition and structure similar to the parent material.The elevated tensile strength of the joint reached 74% of that of the parent metal and the fracture surface exhibited obvious dimple characteristic.The elevated endurance strength of the joint also reached 70% above that of the parent metal.

Corrosion Behavior of Pure Mg and Mg-Li Alloy in 3.5%NaCl of pH=7

HUANG Xiao-mei, ZHANG Chun-hong, ZHANG Min-lin

2008, 28(3): 71-76.

[Abstract](1219) [PDF 2042KB](437)

Abstract:
Corrosion behavior of pure Mg and Mg-Li Alloy in 3.5% NaCl solution of pH=7 was investigated through open circuit electrode potential vs time curve,polarization curve and impedance spectroscopy.The corrosion surface appearances were analysed by SEM,the surface components of pure Mg and Mg-Li alloy before and after corrosion were characterized by XRD,and the average corrosion velocity was detected by means of weight loss.The results indicated that pure Mg had less corrosion current,larger corrosion potential and electrochemistry reactive resistance than those of Mg-Li alloy in early stage of corrosion,but average corrosion velocity of pure Mg was larger than that of Mg-Li alloy after 24 h corrosion and the corrosion appearances were different.A few big and deep corrosion pits were formed on the surface of pure Mg,while the surface of Mg-Li alloy turned black and there were many little and shallow corrosion pits on it.The corrosion product on pure Mg surface was mainly Mg(OH)2,the corrosion products on Mg-Li alloy surface were consisted of Mg(OH)2,LiOH,MgLi,Mg3Li7,Al2O3.

Acceleration Corrosion Factor For Aluminum Alloys:Model and Analysis

HE Xiao-fan, LIU Wen-ting, YANG Hong-yuan

2008, 28(3): 77-81.

[Abstract](1180) [PDF 1736KB](273)

Abstract:
The statistical analysis of acceleration corrosion factor for accelerated aging test to service or natural exposure environment on aluminum alloys is performed.The acceleration corrosion factor is the ratio of service time to accelerated time corresponding to the same corrosion depth.Assuming the corrosion depth follow the logarithmic normal distribution,and the relationship between the corrosion depth and the corrosion time can be expressed as a power function,the expression for acceleration corrosion factor are established.The acceleration corrosion factor is proved to be a constant regardless of reliability degree and corrosion time.The distribution of test acceleration corrosion factor is gained,and the confidence intervals of acceleration corrosion factor for LY12CZ aluminum alloys are obtained.

Tensile Behavior of Ti-3Al-4.5V-5Mo Titanium Alloy with α" Martensite

LI Xing-wu, SU Sheng-ming, LU Min-xu, SHA Ai-xue, CHU Jun-peng

2008, 28(3): 82-86.

[Abstract](1206) [PDF 664KB](219)

Abstract:
The tensile behavior of Ti-3Al-4.5V-5Mo with α" martensite was studied.The results show that the alloy with α" microstructures has lower yield strength and higher plasticity.Reorientation of α"martensite occurs during tensile deformation:[010]α"direction parallel with tensile axis while [100]α"direction perpendicular to tensile axis.The increasing of b/√3a shows that the transition of rhombic α" to close-packed hexagonal α' occurs.The transition of α"→α' induced by strain may be second order phase transformation of displacement type,during which the system free energy calculated decreases.

Friction and Wear Behavior of SiC_p/Al Composites Dry Sliding Against GCr15 Steel

LüYi-zhong, WANG Bao-shun, CUI Yan, QU Jing-xin

2008, 28(3): 87-92.

[Abstract](1306) [PDF 711KB](259)

Abstract:
The Al matrix composites reinforced with SiC particles of different volume fraction(15%、25%、35%、45%、55%、65%)were fabricated by pressureless infiltration technique.Effect of SiC particle volume fraction and applied loads on the friction and wear behavior of the composites sliding against GCr15 steel was investigated under dry condition.The wear tests were carried out using a block-on-ring tester at two loads of 196N and 392N under a constant sliding speed of 0.47m/s.The worn surfaces and subsurfaces of composites were analyzed by scanning electron microscope equipped with energy dispersive X-ray spectroscopy.It is observed that the friction coefficient of SiCp/Al composites increased with increasing volume fraction of SiC particle and decreased with increasing applied load.The wear rates of SiCp/Al composites were decreased with increasing SiC volume fraction.The results showed that the wear rates of SiCp/Al composites were much lower than those of aluminum alloy,since a mechanical mixed layer(MML)was found on the worn surface of SiCp/Al composites.The thickness of MML increased with increasing volume fraction of SiC particle and applied load.When increasing applied load,cracks were found in the MML which results in delamination wear.The wear mechanism of the composites is characterized by abrasive wear,oxide wear and delamination wear.

Study on Contact Fatigue Behavion of 9Cr13Ni6Co5Be Steel

JIN Jian-jun, GU Bao-zhu, FENG Shen-tian, GU Li-xin, RUN Chang-shen, MENG Wei-dong, ZHAO Yan-ming, LEI Jian-zhong

2008, 28(3): 93-96.

[Abstract](1158) [PDF 292KB](221)

Abstract:
Using thrust stressed device,the contact fatigue behavior of 9Cr13Ni6Co5Be steel has been studied.The relationship between the contact stress and fatigue life under different failure probabilities has been secured,and the P-S-N curves are provided.As failure probabilities are equal to 0.01,0.05,0.10 and 0.50,the relationship between the contact stress and fatigue life are N=3.0930×1042×S-9.9602、N=2.9196×1039×S-9.0090、N=1.6505×1038×S-8.6133 and N=1.0679×1035×S-7.5988 respectively,the contact fatigue limits(specified fatigue life 5×107)are 3112 MPa,3358 MPa,3493 MPa and 3950 MPa,respectively.

2008 Vol. 28, No. 3