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Effects of Strontium,Magnesium Addition,Temperature Gradient,and growth Velocity on Al-Si eutectic growth in a Unidirectionally-solidified Al-13 wt%,Si Alloy

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Journal of Materials Science & Technology 2014年第2期30卷 146-153页

作者： Hengcheng Liao Wanru Huang Qigui Wang Fang Jia School of Materials Science and Engineering Southeast UniversityJiangsu Key Laboratory for Advanced Metallic Materials Materials Technology GM Global Powertrain Engineering School of Mechanical Engineering Southeast University

Al-Si eutectic growth mechanism was investigated in a directionally-solidified AI-1 3 wt% Si alloy with different strontium （Sr） and magnesium （Mg） additions, growth velocities and temperature gradients. Macro- and micro- scale metallographic analyses revealed that addition level of Sr and Mg, temperature gradient and growth velocity are important factors affecting stability of solidifying AI-Si eutectic front and the final morphology of eutectic grains in the solidified A1-13 wt% Si alloys. By varying （tailoring） these factors, a variety of eutectic grain structures and morphologies such as planar front, cellular structure, a mix of cellular and columnar, or equiaxed dendrites, can be obtained. Increasing temperature gradient, reducing growth velocity, or decreasing Sr and Mg contents is beneficial to stabilizing planar growth front of eutectic grains, which is qualitatively in accordance with constitutional supercooling criterion for binary eutectic growth. In contrast, adding more Sr and Mg, increasing growth velocity, or decreasing temperature gradient produces large constitutional supercooling, leading to columnar-equiaxed transition （CET） of eutectic structure, which can be interpreted on the basis of Hunt＇s Model. It is also found that both solute concentration and solidification variables have significant impact not only on eutectic growth, but also on gas porosity formation.

关键词： Al-Si alloy Directional solidification eutectic growth Strontium Magnesium Temperature gradient growth velocity

Study on Lattice Parameter Variance and eutectic Reaction during Crystal growth of Nd,Cr∶GSGG by Czochralksi Method

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Journal of Rare Earths 2006年第z1期24卷 140-143页

作者： Zhang Qingli Yin Shaotang Sun Dunlu Shao Shufang Gu Changjiang Crystal Laboratory Anhui Institute of Optics and Fine MechanicsChinese Academy of SciencesHefei 230031China

During the crystal growth of Nd,Cr∶GSGG by Czochralski method,in some cases eutectic reaction occurred in the nether region of the crystal,and the boule was divided into two obvious different parts,which is upper Nd,Cr∶GSGG crystal and the nether coexisting Nd,Cr∶GSGG and GdScO_(3).By X-ray powder diffraction,the structure change of NdCr∶GSGG crystal ofΦ27 mm×120 mm with eutectic along its grown directionwas *** the least square method and extrapolation function f=sinθ-sinθ^(1-t)(t is an adjustable parameter),the lattice parameters of Nd,Cr∶GSGG and additional GdScO_(3)phase were *** results indicate that the lattice parameters of Nd,Cr∶GSGG increase along its growth direction,which changes from a=(1.25650±0.00007)nm of the top to(1.25798±0.00010)nm of the *** the process of Nd,Cr∶GSGG growth,Gd^(3+)in Nd,Cr∶GSGG is partly replaced by Nd^(3+)with larger ionic radii,and the volatilization of Ga component results in its composition variance,which cause the lattice parameters increase along growth *** the eutectic section,there are the Nd,Cr∶GSGG and the second phase orthorhombic GdScO_(3).The lattice parameters of GdScO_(3)are a=0.5443±0.0007,b=0.5699±0.0005 and c=(0.7865±0.0009)nm,and that of Nd,Cr∶GSGG is(1.25798±0.00010)*** the final growth stage,excessive volatilization of Ga composition during the crystal growth causes the growth melt deflect of the Nd,Cr∶GSGG solid solution range seriously,and results in the eutectic reaction,and the outgrowth of Nd,Cr∶GSGG and GdScO_(3).So it is necessary to decrease the effect of gallium volatilization during the growth in order to avoid eutectic growth and obtain a high-quality Nd,Cr∶GSGG.

关键词： Nd,Cr:GSGG eutectic growth lattice parameter X-ray diffraction

Microstructural Evolution of Rapidly Solidified Co-Mo and Ni-Mo eutectic Alloys

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Journal of Materials Science & Technology 2003年第6期19卷 553-556页

作者： Xiujun HAN, Wenjing YAO and Bingbo WEDepartment of Applied Physics, Northwestern Polytechnical University, Xi’an 710072, China Dept. of Appl. Phys. Northwestern Polytech. Univ. Xi'an 710072 China

Droplets of Co-37.6 wt pct Mo and Ni-47.7 wt pct Mo eutectic alloys were rapidly solidified during containerless processing in a 3 m drop tube. A kind of anomalous eutectic appears in these two eutectic alloys when undercooling is beyond 56 and 61 K, respectively. The two eutectic phases in anomalous eutectic were observed to grow in dendrite manner. The formation of anomalous eutectic is ascribed to the cooperative dendrite growth of the two independently nucleated eutectic phases. Current dendrite and eutectic growth theories are applied to describe the observed processes.

关键词： Rapid solidification eutectic growth Dendrite growth Containerless processing

Effect of Rare Earths on Solidification Microstructure and High Temperature Mechanical Property of Sn60-Pb40 Solder alloy

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Journal of Rare Earths 2000年第4期18卷 289-292页

作者：马鑫钱乙余 Harbin Inst Technol Natl Key Lab Welding Harbin 150001 Peoples R China Natl Key Lab Reliabil Phys Elect Prod Guangzhou 510610 Peoples R China Hiroshima Univ Dept Mech Engn Higashihiroshima 724 Japan

Trace rare earth elements were used in order to strengthen the Sn60 Pb40 solder alloy. The experimental results show that the high temperature tensile strength of near eutectic Sn60 Pb40 solder alloy is increased by about 70% after adding trace rare earth elements. Analysis shows that the high affinity between rare earth element and Sn leads to the variation of contact angle at the three phase junction of S/L interface during eutectic growth and further changes the Pb concentration at the S/L interface needed for coupled eutectic growth. Thus the eutectic microstructure can directly grow upon the primary Pb rich phase and the formation of coarse Sn rich halo is suppressed. Therefore homogeneous metallurgical microstructure can be obtained.

关键词： rare earths high temperature tensile strength eutectic growth microstructure

Microstructural evolution of ternary Ag33Cu-42Ge25 eutectic alloy inside ultrasonic field

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Progress in Natural Science:Materials International 2014年第5期24卷 642-648页

作者： Wei Zhai Xiaoyu Lu Bingbo Wei Department of Applied Physics Northwestern Polytechnical University

Ultrasonic field with a frequency of 20 k Hz is introduced into the solidification process of ternary Ag33Cu42Ge25 eutectic alloy from the sample bottom to its top. The ultrasound stimulates the nucleation of alloy melt and prevents its bulk undercooling. At low ultrasound power of 250 W,the primary ε2phase in the whole alloy sample grows into non-faceted equiaxed grains, which differs to its faceted morphology of long strip under static condition. The pseudobinary(Ag t ε2) eutectic transits from dendrite shape grain composed of rod type eutectic to equiaxed chrysanthemus shape formed by lamellar structure. By contrast, the ultrasound produces no obvious variation in the morphology of ternary(Ag t Ge t ε2) eutectic except a coarsening effect. When ultrasound power rises to 500 W, divorced ternary(Ag t Ge t ε2) eutectic forms at the sample bottom. However, in the upper part, the ultrasonic energy weakens, and it only brings about prominent refining effect to primary ε*** microstructural evolution mechanism is investigated on the cavitation, acoustic streaming and acoustic attenuation.

关键词： Dynamic solidification Cavitation effect Ternary alloy Nucleation eutectic growth

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Microstructural evolution during containerless rapid solidification of Co-Si alloys

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Chinese Physics B 2003年第11期12卷 1272-1282页

作者：姚文静魏炳波 LaboratoryofMaterialsScienceinSpace DepartmentofAppliedPhysicsNorthwesternPolytecbnicalUniversityXi'an710072China

The Co-12%Si hypoeutectic, Co-12.52%Si eutectic and Co-13%Si hypereutectic alloys are rapidly solidified in a containerless environment in a drop tube. Undercoolings up to 207K (0.14TE) are obtained, which play a dominant role in dendritic and eutectic growth. The coupled zone around Co-12.52%Si eutectic alloy has been calculated, which covers a composition range from 11.6 to 12.7%Si. A microstructural transition from lamellar eutectic to divorced eutectic occurs to Co-12.52%Si eutectic droplets with increasing undercooling. The lamellar eutectic structure of the Co-12.52%Si alloy consists of εCo and Co3Si phases at small undercooling. The Co3Si phase cannot decompose completely into εCo and αCo2Si phases. As undercooling becomes larger, the Co3Si phase grows very rapidly from the highly undercooled alloy melt to form a divorced eutectic. The structural morphology of the Co-12%Si alloy droplets transforms from εCo primary phase plus lamellar eutectic to anomalous eutectic, whereas the microstructure of Co-13%Si alloy droplets experiences a `dendritic to equiaxed' structural transition. No matter how large the undercooling is, the εCo solid solution is the primary nucleation phase. In the highly undercooled alloy melts, the growth of εCo and Co3Si phases is controlled by solutal diffusion.

关键词： rapid solidification containerless processing Co-Si alloy eutectic growth