航空材料学报

Melt Treatment Time on Microstructure and Mechanical Properties of As-cast Ni-based Superalloy K465

YU Qian, XIAO Cheng-bo, SONG Jin-xia, WANG Ding-gang, XING Zhan-ping, ZHANG Hong-wei, QU Shi-yu, LI Qing

2005, 25(1): 1-4.

[Abstract](1543) [PDF 823KB](247)

Abstract:
The changes of size,distribution and morphology of carbides and γ' phases in Ni-based superalloy K465 after 1-10min melt treatment were investigated by optical metallography and scanning electron microscopy.The tensile properties at R.T.and high temperature stress rupture properties of alloy K465 were carried out to evaluate the effect of melt treatment.The results show that the size of carbides and γ' phases in dendritic areas can be decreased by melt treatment.The good comprehensive properties can be achieved by the melt treatment of 5-7min by improving the homogeneity distribution of carbides and cubic effect of γ' phases in dendritic areas.

Microstructure Evolution and Fracture Behavior in Superplastic Deformation of Hot-rolled AZ31 Mg Alloy

ZHANG Kai-feng, YIN De-liang, WANG Guo-feng, HAN Wen-bo

2005, 25(1): 5-10.

[Abstract](1489) [PDF 1473KB](245)

Abstract:
Fine-grained AZ31 magnesium alloy sheets were prepared through hot rolling process.The super-plastic deformation behavior of hot-rolled AZ31 magnesium alloy was investigated at a temperature range 250-450℃ and an initial strain rate range 0.7 ×10-3~1.4 ×10-1s-1.Optical microscope and scanning electronic microscope(SEM)were employed to observe the microstructure evolution and fracture behavior in superplastic deformation of AZ31 Mg alloy and the values of deformation activation energy at various temperatures were calculated.It is shown that the hot-rolled AZ31 Mg alloy begins to exhibit superplasticity from 300℃ and the maximum elongation of 362.5% is obtained at 400 ℃ and an initial strain rate of 0.7 × 10-3s-1.In the temperature range 300-400℃ for super plastic deformation of AZ31 Mg alloy,the predominate deformation mechanism is grain boundary sliding(GBS)controlled by grain boundary diffusion and the influences of strain rates and temperatures on the fracture behavior of AZ31 Mg alloy are embodied by the transformation of deformation mechanism from intracrystalline slip to GBS.

Study on Microstructure and Properties of a Ni-Cr-Al Alloy by EB-PVD

GUAN Chun-long, HE Xiao-dong, LI Yao, SUN Ye

2005, 25(1): 11-14.

[Abstract](1484) [PDF 1003KB](270)

Abstract:
Ni-Cr-Al alloy with 0.5mm thickness was deposited by EB-PVD process.Microstructure and mechanical properties were investigated on as-deposited and long-term aged alloy.The results indicate that grain size on surface of as-deposited alloy was about 185nm,and a laminated structure in cross-section was observed.After aging for 16h,72h,120h at 760℃,the laminated structure was dissolved,and the individual grains can been seen clearly.Columnar crystals formed in the surface of alloy ajacent to the substrate,and exquiexed grains apart from the substrate for the alloy after aging for 16h.The major precipitate was γ'phase after prolonged aging at 760℃.Factograghs of as-deposited alloy show that the fracture was mixed type at room temperature.Brittle fracture took place along boundaries of columnar crystals formed in the side adjacent to the substrate.However,in the side apart from the substrate the equiaxed dimples were dominant.Brittle-ductile transition occurred after aging treatment in vacuum condition.Room temperature microhardness of alloy decreased with an increase in temperature mainly due to the growth of-γ'phases.Test results show that compared with as-deposited alloy,mechanical properties of annealed alloy were improved significantly.

Effect of Aging on a Hypoeutectoid CuAlBe SMA

ZHOU Jian, WANG Hai-long, SUN Yang-shan

2005, 25(1): 15-18.

[Abstract](1465) [PDF 978KB](157)

Abstract:
The thermal stability of a hypoeutectoid CuAlBe SMA was studied in this paper.The aged specimens were performed by measuring phase transformation temperature,and observed by OM,SEM and XRD.Firstly,the phase transformation temperature of the alloy shortly aged at 200℃ up to 300℃ ascended with the evolving of the disorder to order transformation.Subsequently,the phase transformation temperature of the alloy sharply dropped with the equilibrium phase a or the nonequilibrium phase α precipitating on condition that the specimens were aged at 200℃ up to 300℃ for a long time or aged over 300℃.

Computer Simulation of Effects of Pouring Temperatures on Cast Grain Structures of Superalloy K4169

YAN Wei-dong, LIU Lin, CHEN Qun-zhi, XIONG Yu-hua, YANG Ai-min

2005, 25(1): 19-24.

[Abstract](1617) [PDF 850KB](245)

Abstract:
Using FDM Fortran program,the temperature evolution on a cross section of superalloy K4169 cylinder ingots was simulated through solving the heat diffusion equation with enthaply formulation.It reflected temperature evolution on the cross section of castings under various founding processes correctly.Using the fraction of solid,the simulation of temperature fields,the continuous nucleation model and growth kinetics model of the dendritic tip were coupled to calculate grain structure features of superalloy K4169 cylinder ingots during solidification at different pouring temperatures.Based on a two-dimensional Cellular Automaton technique and the grain structure features of superalloy K4169 cylinder ingots,the grains nucleation and growth of these castings were displayed on computer screen dynamically.The calculated effect of the pouring temperature on the resultant grain structure agrees well with experimental observations.

Synthesis of Heat-resistant Silicone Resin and Studies on its Thermal and Curing Properties

SUN Ju-tao, HUANG Yu-dong, CAO Hai-lin, GONG Gui-fen

2005, 25(1): 25-29,35.

[Abstract](1686) [PDF 521KB](564)

Abstract:
The silicone resin is synthesized using hydrolysis-polycondensation method from phenyl and methyl chlorosilane,and the factors influencing this synthesis are investigated.The results indicate that silicone resin can be synthesized when the hydrolysis temperature is 70℃ and n(H2O)/n(Cl)is between 5:1 and 8:1.And the IR analysis shows that silicone resin possesses hydroxyl end group.The thermal properties are investigated using thermo-gravimetric analysis(TG),differential thermogravimetric analysis(DTG)and muffle furnace test,and the effects of curing agents,such as KH-CL and triethanolamine,on the thermal properties of silicone resin were also discussed.It is found that silicone resin possesses excellent thermal stability with onset degradation temperature at about 400 ℃,and its mass loss is mainly caused by the "unzipped degradation" occurred between 400-500 ℃,and the "rearranged degradation" occurred after 500 ℃.But it thermal properties decreases at air atmosphere duo to the oxidative-degradation of organic groups.Silicone resin can cure at room temperature with KH-CL,and its thermal stability is improved after cured.

Finite Element Simulation of Key Properties of Three-dimensional and Four-step Braided Composite

WAN Qiong, LI Fu-guo, LIANG Hong, ZHANG Li-li

2005, 25(1): 30-35.

[Abstract](1366) [PDF 811KB](261)

Abstract:
A "lemniscates" micro model is established according to the fabric of the three-dimensional and four-step braided composite.On the base of this model,the distribution of thermal stress and strain of the three-dimensional and four-step composite during the preparation process is analyzed by using FEM software.The effective elastic modulus and the effective thermal expansion coefficient of the three-dimensional and four-step composite at room temperature are simulated and compared with their analytic solution.These results provide an accurate simulation method and give reference to design,process and use this kind of composite.

Preparation of Magnetic Multilayers Microwave Absorbent

ZHU Sheng-bin, LI Yong-qing, CHENG Hai-feng, CAO Yi

2005, 25(1): 36-39,44.

[Abstract](1565) [PDF 621KB](495)

Abstract:
A kind of magnetic multilayers microwave absorbent is prepared with magnetron sputtering.The structure is characterized with scan electric microscope and X-ray diffraction.The permittivity,permeability and density of the absorbent samples are tested.The optimization design of single layer material is performed.The results show that the absorbent has better microwave absorbing capability.

Study on Influence Factors of Contact Corrosion Between Aluminum Alloys and Antiaging Coatings of Rubber

LI Bin, TAO Chun-hu, LI Di, LU Feng, CAI Jian-ping, ZHANG Xiao-yun

2005, 25(1): 40-44.

[Abstract](1463) [PDF 829KB](239)

Abstract:
The effect of environmental temperature,relative humidity,time and the contact type on the contact corrosion between aluminum alloys and antiaging coatings of rubber were studied by the orthogonal experiments.The results demonstrated that environmental temperature,relative humidity,the tightness of contact were the remarkable influential factors for the aluminum alloy corrosion;The contact corrosion happened in environment with high humidity and high temperature when 7A04-T6 aluminum alloy(clad),7A04-T6 aluminum alloy(bare)were contacted compactly with antiaging coatings of rubber.

Study on the Cure Kinetics of Middle Temperature Curing 3234 Epoxy Resin System

LIU Tian-shu, ZHANG Bao-yan, CHEN Xiang-bao

2005, 25(1): 45-47,52.

[Abstract](1339) [PDF 325KB](267)

Abstract:
The cure kinetics of middle temperature curing 3234 epoxy resin system was studied under isothermal and dynamic curing conditions by Differential Scanning Calorimetry(DSC)technique.The cure kinetic equations were established.By simulating practical temperature procedure of curing,the cure kinetic equations were verified by means of determining the residual heat of reaction of samples with different cure degrees.The results showed that the cure kinetics can be described by the autocatalytic kinetic model.The cure kinetic equation obtained from dynamic test agreed well with the experimental results.

Study on Binder Removal Process of Green Bodies of Aqueous Gel-casting

LIU Xiao-guang, TONG Jian-feng, LI Bao-wei, CHEN Da-ming

2005, 25(1): 48-52.

[Abstract](1456) [PDF 718KB](372)

Abstract:
The binder removal process is one of critical steps in the fabrication of aqueous gel casting materials.Effects on binder removal were particularly studied in this paper,and microstructures,and pore distributions of green bodies of aqueous gel casting were also studied.Results show that temperature-increasing rate,holding time,thickness of green bodies and surface areas have a great influence on binder removal process.According to curve of DTA-TG,physical and chemical reactions under binder removal process were analyzed,meanwhile several binder removal processes were compared.

Damping Analysis of Cocured Composites with Interleaved Viscoelastic Layers

ZHANG Shao-hui, CHEN Hua-ling

2005, 25(1): 53-57.

[Abstract](1565) [PDF 446KB](523)

Abstract:
The modal loss factor of cocured laminated composites with embedded viscoelastic layers is predicted using the finite element based modal strain energy method with consideration of frequency dependency of viscoelastic materials.The contribution of energy dissipation of fiber-reinforced composites to the loss of whole system is taken into account in numerical analysis for more accurate results.Good agreements between the present results and those published have suggested the validity of the proposed approach.The effects of damping of fiber-reinforced composites,compliant layering and location of damping layers on the loss factor of damped composite beams have also been studied.Some ways to improve damping properties of cocured laminated composites are presented.

Stress Concentrations and Strengths of Unidirectional Composites at Cryogenic Temperature

ZENG Qing-dun, ZOU Bo

2005, 25(1): 58-62.

[Abstract](1565) [PDF 429KB](231)

Abstract:
Using a modified shear-lag model taking into account the tensile force in the matrix,the stress redistributions induced by the fracture of some fibers and matrix elements for unidirectionally fiber-reinforced composites subjected to axial tension at cryogenic temperature were studied.On the basis of this,utilizing the random critical-core theory,the micro-statistical analysis for the tensile failure of unidirectionally fiber-reinforced composites at cryogenic temperature was performed.The influence of low temperature on the tensile strength was studied quantitatively.The calculating results show that the variation of the stress concentration factors for both E-glass and carbon fiber composites at cryogenic temperature is different and their strengths are higher than those at normal temperature.

2005 Vol. 25, No. 1