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Microstructure Evolution of Cu-Pb Monotectic Alloys Processed in Drop Tube

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Journal of Materials Science & Technology 2002年第1期18卷 73-76页

作者： Cao, CD Wei, BB Northwestern Polytech Univ Dept Appl Phys Xian 710072 Peoples R China

Rapid solidification of Cu-Pb monotectic alloys has been accomplished during free fall in a 3 m drop tube. Both macrosegregated and uniformly dispersed structures are observed in Cu-40 wt pct Pb alloy droplets, whereas droplets of composition Cu-64 wt pct Pb exhibit only macrosegregation morphologies. The microstructures are strongly dependent on droplet size. The higher undercooling tends to facilitate liquid phase separation and results in more extensive macrosegregation in smaller droplets. There exists a pronounced tendency for the Pb-rich liquid to occupy the surface of the droplets of both compositions, resulting from the quite lower surface tension of the Pb-rich phase and causing a Pb-rich layer at the surface of the solidified droplet. The nucleation of monotectic cells in the Cu-40 wt pct Pb droplets with dispersed structures preferentially occurs at the droplet surface. A single nucleation event takes place more frequently as droplet size is reduced.

关键词： Rapid solidification Undercooling Immiscibility containerless processing Low-gravity Monotectic

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

Electrostatic levitation under the single-axis feedback control condition

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Science China(Physics,Mechanics & Astronomy) 2010年第8期53卷 1438-1444,0页

作者： HU Liang WANG HaiPeng XIE WenJun WEI BingBo Department of Applied Physics Northwestern Polytechnical UniversityXi’an 710072China

An electrostatic levitator with a single-axis feedback control system was developed on the basis of electric field analysis and optimum design for levitation electrodes. In order to realize the stable levitation of various types of materials such as metals, inorganic materials and polymers, we made both experimental and theoretical investigations to solve the four key problems of electric field optimization, sample position detecting, sample charging control and levitation voltage minimization. Under the capacitive induction charging condition, a sample with the size of 2.6–4.5 mm usually bears positive charges amounting to 10-9 Coulomb. Because the single-axis feedback control system responds quickly, it takes the levitated sample only 0.1 s from leaving the bottom electrode until attaining a stable levitation in the upright direction. The levitated sample displays satisfactory levitation stability in both the upright and the horizontal directions owing to the constraining force produced by spherical electrodes.

关键词： electrostatic levitation containerless processing feedback control space science

Geometric optimization of electrostatic fields for stable levitation of metallic materials

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Science China(Technological Sciences) 2013年第1期56卷 53-59页

作者： HU Liang WANG HaiPeng LI LiuHui WEI BingBo Department of Applied Physics Northwestern Polytechnical University

Experimental and computational methods are used to optimize the electrostatic field for levitating metallic *** calculated launch voltage increases linearly with the distance between top and bottom *** combination of a larger top electrode diameter with a smaller bottom diameter may enhance the levitation ability because the electric field intensity near the levitated sample is *** convex and bottom concave electrodes can guarantee good levitation stability but decrease the levitation *** design of bottom electrode is crucial to attain not only a stable levitation state but also a higher levitation *** a measure characterizing the intrinsic levitation ability of various materials,the product of density and diameter of levitated samples can be used to determine the launch voltage for counteracting gravity according to a power relationship.

关键词： electrostatic levitation containerless processing capacitive induction space science

STUDY ON DYNAMIC CHARACTERISTICS OF ACOUSTIC LEVITATION

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Chinese Journal of Aeronautics 1998年第3期11卷 69-75页

作者：高建荣曹崇德魏炳波 Lab. of Materials Science in Space Department of Applied Physics NW Polytechnical University Xi' an 710072 China

The dynamic characteristics of acoustic levitation were investigated for the purpose of containerless processing of materials. Experimental measurements were accomplished on the variations of sound pressure level with both axial position z (6.5mm≤ z ≤27.5mm) and radial position r (1mm≤ r ≤16mm) in a cylindrical resonant tube(34mm×45mm) of a single axis acoustic levitator. The results showed that the minimum sound pressure levels in both axial and radial directions occur at the centres of two transverse intercepting planes with z =8.5mm and z =21.5mm, which were identified as the sound pressure nodes not only of the axial direction but also of the radial direction, and hence were expected to have good levitation stability. This was further proved by experimental observations.

关键词： containerless processing acoustic levitation sound pressure levitation stability

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 CoaSi 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 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

Rapid dendritic growth of Al-Ge hypoeutectic alloy in a drop tube

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Progress in Natural Science:Materials International 2003年第2期 79-82页

作者： LIU Xiangrong, CAO Chongde and WEI Bingbo(Department of Applied Physics, Northwestern Polytechnical University, Xi’an 710072, China) Department of Applied Physics Northwestern Polytechnical University Xi'an 710072 China

Abstract Dendritic growth in Al-45% Ge hypoeutectic alloy has been investigated during free fall in a 3 m drop tube. Calculationsindicate that the undercooling obtained for the falling Al-45% Ge droplets ranges from 13 K to 201 K. The maximum undercooling attains0. 27 TL. With the increase of undercooling, the primary (Al) phase undergoes a "columnar dendrite to equiaxed dendrite" structural tran-sition. According to the current rapid dendritic growth theory, the growth of primary (Al) phase is always controlled by solute diffusion.

关键词： dendritic growth undercooling containerless processing Al-Ge alloy.

Rapid Solidification from the Undercoold Melt of Fe-Rare Earth Magnetostriction Alloys

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Rapid Solidification from the Undercoold Melt of Fe-Rare Ear...