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Formation of twinned dendrites during unidirectional solidification of Al-32%Zn alloy

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Transactions of Nonferrous Metals Society of China 2018年第4期28卷 802-811页

作者： Zhong-wei CHEN Jian-ping GAO State Key Laboratory of solidification Processing Northwestern Polytechnical UniversityXi’an 710072China

The present study focused on the formation and crystallographic orientation of twinned dendrites coexisting with equiaxed grains in unidirectional solidification of Al-32%Zn(mass fraction)*** morphology was investigated by optical metallograph and electron back-scattered diffraction *** showed that the macrostructure of the alloy exhibited a typical feathery and fan-like structure while the microstructures were elongated lamellas,which were separated by coherent and incoherent twin *** the primary trunk and all lateral arms of twinned dendrites grew along〈110〉directions,unlike regular〈100〉α(Al)*** facet growth of crystals at solid/liquid interface was responsible for the origin of twinned dendrites during the weak local convection,and high thermal gradient and medium solidification velocity had significant contribution to the formation of twinned *** formation mechanism of twinned dendrites which consisted of three multiplication ways of new twin boundaries formation and one way of dendrite evolution in twin plane was shown schematically.

关键词： unidirectional solidification twinned dendrite growth direction aluminum alloy

Macrostructure and properties of thin walled copper tubes prepared by the downward continuous unidirectional solidification method

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International Journal of Minerals,Metallurgy and Materials 2010年第1期17卷 63-68页

作者： Xi Shen Hong Zhang Zi-dong Wang Hua-fen Lou Yi-ming Jia Ping-xia Hu School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China CHINALCO Luoyang Copper Co. Ltd. Luoyang 471000 China

The macrostructure and properties of the thin walled copper tube prepared by the downward continuous unidirectional solidification （DCUS） method were studied. The result shows that the macrostructure is closely related to the solid-liquid interface profile, which is influenced by the distance between the cooling water location and the solidification front. The mechanical properties of the thin walled copper tube prepared by the DCUS method are near those of the normal cast copper, and it has good relative density, electrical conductivity, and elongation, which are not greatly affected by casting speed. The thin walled copper tube prepared by the DCUS method also has good processing properties that can be taken to further drawing procedures directly without an intermediate process, and obtains good mechanical properties with the total processing rate of 89.8%.

关键词： unidirectional solidification copper tube short process macrostructure mechanical properties

Simulation of stray grain formation during unidirectional solidification of IN738LC superalloy

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Journal of Central South University 2011年第1期18卷 23-28页

作者：李响妹张捷宇王波任忠鸣周国治 Shanghai Key Laboratory of Modern Metallurgy and Materials Processing Shanghai University School of Metallurgical and Ecological Engineering Beijing University of Science and Technology

The influence of casting parameters on stray grain formation of a unidirectionally solidified superalloy IN738LC casting with three platforms was investigated by using a 3D cellular automaton-finite element （CAFE） model in CALCOSOFT package. The model was first validated by comparison of the reported grain structure of AI-7%Si （mass fraction） alloy. Then, the influence of pouring temperature, heat flux of the lateral surface, convection heat coefficient of the cooled chill and mean undercooling of the bulk nucleation on the stray grain formation was studied during the unidirectional solidification. The predictions show that the stray grain formation is obviously sensitive to the pouring temperature, heat flux and mean undercooling of the bulk nucleation. However, increasing the heat convection coefficient has little influence on the stray grain formation.

关键词： computer simulation unidirectional solidification stray grain grain structure

Effect of melt superheat on structural uniformity of lotus-type porous metals prepared by unidirectional solidification

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Transactions of Nonferrous Metals Society of China 2015年第3期25卷 1004-1010页

作者：刘源张华伟李言祥清华大学材料学院北京100084 先进成形制造教育部重点实验室北京100084

Structural uniformity is an important parameter influencing physical and mechanical properties of lotus-type porous metals prepared by directional solidification of metal-gas eutectic (Gasar). The effect of superheat on structural uniformity as well as average porosity, pore morphology of porous metals was studied. The experimental results show that, when the superheat is higher than a critical value (ΔTc), the bubbling or boiling phenomenon will occur and the gas bubbles will form in the melt and float out of the melt. As a result, the final porosity will decrease. In addition, a higher superheat will simultaneously cause a non-uniform porous structure due to the pores coalescence and bubbling phenomenon. Finally, a theoretical model was developed to predict the critical superheat for the hydrogen to escape from the melt and the corresponding escapement ratio of hydrogen content. Considering the escapement of hydrogen, the predicted porosities are in good agreement with the experimental results.

关键词： unidirectional solidification porous metals melt superheat structural uniformity

Microstructure Evolution of Cu-6%Ag Alloys by Modified unidirectional solidification Under a Horizontal Static Magnetic Field

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Journal of Iron and Steel Research International 2012年第S1期19卷 248-251页

作者： ZUO Xiao-wei ZHAO Cong-cong MA Ming WANG En-gang HE Ji-cheng Key Laboratory of Electromagnetic Processing of Materials(Ministry of Education) Northeastern University

The microstructure evolution of Cu dendrites in Cu-6%Ag alloys by modified unidirectional solidification under a static magnetic field has been investigated experimentally and *** results show that the proeutectic Cu dendrites are finer when they are closer to the water-cooling copper mould and the unidirectional effect is more obvious,which is attributed to the higher solidification *** quantitative analysis of the microstructure indicates that with increasing external magnetic flux density,the primary arms of the proeutectic Cu dendrites are refined and along a given *** analysis indicates that it is both the thermoelectromagnetic convection effect by the external magnetic field and the branch effect of the dendrites.

关键词： Cu-Ag unidirectional solidification microstructure evolution static magnetic field

INTERFACE MORPHOLOGIES AND SOLUTE SEGREGATION OF Al-Li ALLOY 8090 DURING unidirectional solidification

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Acta Metallurgica Sinica(English Letters) 1993年第2期6卷 73-77页

作者： LIU Yulin ZHANG Yun ZHAO Hong’en HU Zhuangqi SHI Changxu Institute of Metal Research,Academia Sinica,Shenyang,China Associate Professor,Institute of Metal Research,Academia Sinica,Shenyang 110015,China

The solid-liquid interface morphology and solute segregation behaviour of AI-Li alloy 8090 during unidirectional solidification were studied by the liquid metal quenehing method under varied processing *** solidification rate,RO.75 mm/min (temper- ature gradient,G_L=130℃/cm),the structure revealed of planar or dendritic interface *** the increase of R,the interface morphology becomes cellular from planar gradually,within a narrow *** the greater the R,the,finer the *** of element Cu and impurity elements Fe and Si are quite severe,the interface morphology markedly influences on solute *** solidification at coarse dendrite interface, their segregation ratios are rather great and solidified structure is coarse.

关键词： Al-Li alloy unidirectional solidification interface morphology solute segregation alloy 8090

History-dependence of cellular-dendritic transition during unidirectional solidification

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Progress in Natural Science:Materials International 1997年第6期 111-114页

作者：丁国陆黄卫东周尧和 China Northwestern Polytechnical University State Key Laboratory of solidification Processing Xi’an 710072

Recently, both theoretical analyses and experimental researches of planar-cellular transition found a subcritical bifurcation for k00.45, where K0is the equilibrium solute partition coefficient. Therefore, it is not difficult to argue that cellular-dendritic transition, which deviates farther from equilibrium than the planar-cellular one, should have similar bifurcation characteristics and happen not at a unique velocity point but in a

关键词： cellular-dendritic transition unidirectional solidification history-dependence.

Analysis on the Ceasing Mechanism of the YBCO Crystal Growth during Melting Growth Process by unidirectional solidification

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Analysis on the Ceasing Mechanism of the YBCO Crystal Growth...

Nature of large (Ti, Nb)(C, N) particles precipitated during the solidification of Ti, Nb HSLA steel

International Conference on Superconducting Materials(ICSM 2006)

作者： Haitao Cao,Rui Hu,Hongchao Kou,Jinshan Li,Enzhi Gao, Hengzhi Fu,Lian Zhou State Key Lab. of solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China Northwest Institute for Nonferrous Metal Research, Xi'an 710016,China

The unidirectional solidification technology by a zone melting method was performed to obtain the large single domain YBCO. The interface morphology and chemical composition at the growth front of the YBCO crystal were investigated in order to make clear the growth characteristic of the YBCO crystal during melting growth by unidirectional solidification. It was found that YBCO crystal would cease growing when yttrium was depleted in the liquid phase at the YBCO crystal growth front. For maintaining the continuous growth of YBCO crystal, compositions of Y, Ba and Cu in raw samples have to be adjusted so as to make yttrium rich in the liquid phase at the YBCO crystal growth front during the melting growth process. It is very useful for the study on the mechanism of the YBCO crystal growth.

关键词： unidirectional solidification Ceasing mechanism YBCO Single domain

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Journal of University of Science and Technology Beijing 2007年第2期14卷 112-117页

作者： Xiaojun Zhuo Xinhua Wang Wanjun Wang Hae-Geon Lee Metallurgical and Ecological Engineering School University of Science and Technology Beijing Beijing 100083 China Graduate Institute of Ferrous Technology Pohang University of Science and Technology Pohang 790-784 South Korea

To investigate the microsegregation phenomena and complex （Ti, Nb）（C, N） precipitation behavior during continuous casting, a unidirectional solidification unit was employed to simulate the solidification process. The samples of Ti, Nb-addition steels after unidirectional solidification were examined using field emission scanning electron microscope （FE-SEM） and electron probe X-ray microanalyzer （EPMA）. In such specimens, dendrite structure and mushy zone can be detected along the solidification direction. It shows that the addition of titanium, niobium to high-strength low-alloyed （HSLA） steel results in undesirable （Ti, Nb）（C, N） precipitation because of microsegregation. The effect of cooling rate on （Ti, Nb）（C, N） precipitation was investigated. The composition of large precipitates was determined using FE-SEM with EDS. Large （Ti, Nb）（C, N） precipitates could be divided into three kinds according to the composition and morphology. With the cooling rate increasing, Ti-rich （Ti, Nb）（C, N） precipitates are transformed to Nb-rich （Ti, Nb）（C, N） precipitates.

关键词： carbonitride microsegregation dendritic region unidirectional solidification cooling rate