航空材料学报

SOLIDIFICATION BEHAVIOUR OF Ni-BASE SINGLE-CRYSTAL SUPERALLOY DD2

Du Wei, Wei Pengyi, Li Jianguo, Fu Hengzhi, Sun Jiahua

1997, 17(2): 1-6.

[Abstract](1375) [PDF 440KB](245)

Abstract:
With the help of high-temperature-gradient directional solidification equipment (LMC), the solidification behavior under high temperature gradient of DD2 single crystal superalloy was investigated. The morphology of liquid/solid interface during solidification, primary dendrite arm spacing and side-branch coarsening kinetics, and microstructure were examined in specimens obtained under different growth rate. Theresults show that, when the temperature gradient keeps constant, with the increase of the growth rate,single crystal specimens of DD2 reveal the planar, cellular and dendrite interface structure in sequence-The primary dendrite arm spacing decreases with the increase of cooling rate. The amount of γ/γ’eutecticin fine dendrite is larger but smaller in size than that in the coarse dendrite. When the cooling rate is much higher, superfine columnar dendrite are formed, and the amount of γ/γ’eutectic decreased.

STRUCTURE AND PROPERTIES OF IN-SITU SURFACE COMPOSITES OF Al-20wt%Si ALLOY FABRICATED BY CENTRIFUGAL CASTING

Wang Qudong, Jin Junze

1997, 17(2): 7-13.

[Abstract](1330) [PDF 625KB](344)

Abstract:
In situ three-layer surface composites of Al-20wt%Si alloy which possesses the microstructure of accumulated thick primary Si in outer layer, accumulated fine primary Si in inner layer, and eutectic in middle layer,has been achieved by preheated metal mould centrifugal casting. The structure morphology of thecomposites has been investigated, the hardness,wearability and fracture model of the composites have been analysed.

INVESTIGATION ON PRIMARY CRYSTALLIZATION OF RAPIDLY SOLIDIFIED Al₈₈Ce₂Ni₇Fe₃ AMORPHOUS ALLOY

Song Guangsheng, Yang Gencang, Zhou Yaohe, Meng Qingcang, Shen Jun, Li Qingchun

1997, 17(2): 14-19.

[Abstract](1397) [PDF 484KB](188)

Abstract:
The early stage in the crystallization process of rapidly solidified Al88Ce2Ni7Fe3 amorphous aluminum alloy found by X-ray diffraction and transmission electron microscopy is a primary crystallization. The variation of volume fraction and partic1e size of nanocrystalline α-Al exhibit different behaviour:the former increases gradually and the latter keeps almost unchanged. From small angle X-ray scattering results of different annealed samples, it is concluded that nanocrystalline α-Al particles precipitated in the amorphousmatrix occur transformation of rare distribution at low temperature to concentrated distribution at high temperature-According to these results, the characteristics of volume fraction, grain number, particlesize and particle distribution of α-Al in the primary crystallization process have been analysed and dis-cussed, which provides a physical view for α-Al strengthening in the amorphous matrix.

THE MICROSTRUCTURE AND PROPERTY OF RAPIDLY SOLIDIFIED Al-Cr-RE ALLOYS

Mi Guofa, Zeng Songyan, Jiang Zuling, Li Qingchun

1997, 17(2): 20-25.

[Abstract](1385) [PDF 548KB](197)

Abstract:
Four kinds of alloy ribbons Al-(4~10wt%)Cr-4wt%RE(RE denotes La-richmisch metal) were madeon rapid cooling apparatus with monoroller under the similar experimental conditions. The phases presented and microstructure of the rapidly solidified alloy were studied. By X-ray diffraction, TEM, electronicprobe and energy spectrum analysis The microhardness of the alloy was measured with microhard-nessmeter. The strength limit of the ribbons were also measured with electronic tensometer. The experi-ment showed that Al-(4~6wt%)Cr-4wt%RE alloy appear to be prospects in the future.

STRESS INDUCED FORMATION OF MARTENSITE IN Ti-10V-2Fe-3Al ALLOY

Shen Guiqin, Zhang Hong, Wang Shihong, Liang Youming

1997, 17(2): 26-31.

[Abstract](1423) [PDF 517KB](232)

Abstract:
The Characteristics of stress-induced martensitic transformation in various solution treated Ti-1023 alloy during tensile deformation had been studied.The crystallographic structure of trans formation products and the triggering stress have been measured lt was found that the transformation behaviors are closely related to both solution treating temperature and cooling rate. Finally, the effects of stress-inducedmartensite transformation on tensile properties were discassed.

STUDY ON FRACTURE OF SUPERPLASTIC DEFORMATION IN LF6

Long Nidong

1997, 17(2): 32-39.

[Abstract](1348) [PDF 637KB](233)

Abstract:
The microstructural change and fracture morphology during superplastic deformation of LF6 Aluminium alloy have been examined. The experimental results show that cavities mainly nucleate at triple points and grow continuously with the increase of strain, at the same time, new cavities occllred. Grain boundarysliding is the main cause of cavity growth. Because of high strain rate sensitivity, the alloy can preventcavitise from propagation and interlinkage along transverse grain boundaries. Only at the later stage of deformation, cavities begin to interlink and propagate extensively along transverse grain boundaries, which isdue to the increase in local stress of the weakpart of the tensile sample, causing the fracture of the alloy.The grain growth and elongation in the tension direction during deformation may promote cavity nucleation. A physical model of superplastic de formation fracture of the alloy is presented.

NUMERICAL ANALYSIS OF THE EFFECTS OF INTERLAYER WIDTH ON THE STRESS DISTRIBUTION IN DIFFUSION BONDED CERAMICS JOINTS

Chang Baohua, Shi Yaowu

1997, 17(2): 40-44.

[Abstract](1438) [PDF 312KB](156)

Abstract:
Stresses distributions of diffusion bonded joints with interlayer are studied using the finite element method. the curves of normal stress and shear stress distribution are obtained for joints with different interlayer width under plane stress condition and plane strain condition. The results show that when thewidth of the interlayer is small the normal stress and shear stress distribute almost uniformly, with the increase of the interlayer width, where the normal stress increases and has a peak value in the middle part ofthe specimen under plane strain condition, and has a peak value on the edge of the free end of a specimenunder plane stress condition. the shear stresses of both stress conditions increase with the increase of thedistance from the central line of a specimen. The maximum of the shear stress near the edge of a specimenincreases with the increase of interlayer width. lt is concluded that a small width of interlayer should beadopted under the condition that the joints are well bonded.

DESIGN OF THE SPECIMENS FOR MODELING MULTIAXIAL STRESS STATES FOR Ni-BASE SINGLE CRYSTAL SUPERALLOYS

Yue Zhufeng, Han Hongxian, LüZhenzhou

1997, 17(2): 45-49.

[Abstract](1445) [PDF 288KB](253)

Abstract:
Based on the anisotropic crystallographic finite element analyses, some mulitiaxial stress specimens are considered. The thin-walled tubular specimens and plate shear specimens are not suitable for the single crystal superalloys, owing to the single shear stress state could not be occured. With a special sizes, thenotched double shear specimens can he used to model the multiaxial stress stares. In this paper, the size of the specimen has.been analyzed, and the analytical equations for resolved shear stress and shear strain are presented. The experimental results of double shear tests show that there are striking dependence of creep behavior on crystallographic orientations in the multiaxial stress states.

THE PROPERTIES AND SUPERPLASTIC DEFORMATION OF SPRAY-ATOMIZATION AND CO-DEPOSITION SiC_p/LY12 MMCs

Li Miaoquan, Chen Dunjun, Chen Yanyun, Tang Cairong

1997, 17(2): 50-55.

[Abstract](1407) [PDF 436KB](182)

Abstract:
In the paesent paper, the micrographs and limited strength of 10vol% SiCp/LYl2 spray atomization and co-deposition MMCs are investigated. The superplasticity of this materiaI after HIP and hot extrution is also studied. This spray-atomized material has good superplasticity after pretreatment and the strain rate sensitivity index m and the limited elongation were found to be 0.53 and 345%, respectively. The nucleation and growing of cavities do exist all the time during the superplasitc deformation and the growing and interlinkage of the cavities have important influence on the fracture of the material.

1997 Vol. 17, No. 2