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Effects of Ca and Nd addition on plastic instability in extruded Mg-Mn alloy deformed under various conditions

Journal of Magnesium and Alloys 2023年第2期11卷 543-552页

作者： Sang Kyu Woo Risheng Pei Talal Al-Samman Dietmar Letzig Sangbong Yi institute of Materials and Process Design Helmholtz-Zentrum hereon21502 GeesthachtGermany Institut für Metallkunde und materialphysik RWTH Aachen University52056 AachenGermany

Plastic instability, called Portevin-Le-Chatelier(PLC) effect, manifests itself as an unstable plastic flow during tensile tests of structural materials. This phenomenon has a strong influence on diverse properties, leading to unexpected vulnerabilities in the service *** various magnesium-based alloys, PLC phenomenon is most prominently observed in the Mg-Mn-Nd alloy under elevated temperature and low strain rate conditions. An important aim of the study is to clarify and compare the significance of the RE and Ca addition, which are known to cause a formation of a largely weakened non-basal type texture, in the occurrence of plastic instability. Due to the PLC phenomenon, there is a risk of weakening texture and formability improvement by the addition of RE and Ca elements in Mg alloys. Based on the understanding of the role of Nd to the PLC phenomenon in Mg-Mn alloy identified in previous studies, the PLC characteristics according to alloying elements and deformation conditions were compared and analyzed. To identify the micromechanical mechanisms of the PLC phenomenon, varies in the microstructure and mechanical properties during deformation of Mg-Mn binary and Ca or Nd-containing Mg-Mn-based ternary alloys in various conditions were systemically analyzed. The addition of Ca did not show a marked PLC effect due to the formation of low number density Mn-Ca and Ca-Ca solute clusters and an unbalanced Mn:Ca ratio. In contrast, the addition of Nd leads to the formation of a higher number density of Nd-Nd and Mn-Nd solute clusters than that of Ca-Ca and Mn-Ca solute clusters of the Mg-Mn-Ca alloy, resulting in a stable solute-dislocation interaction atmosphere under specific ranges of deformation temperature and strain rate. The deformation in the regime of PLC phenomenon, results in a decrease in ductility and an increase in strength, despite deformation at elevated temperatures with maintaining the weakened texture.

关键词： Magnesium Plastic instability Portevin-Le Chatelier effect Solute cluster Neodymium Calcium

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Plastic instability and texture modification in extruded Mg-Mn-Nd alloy

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Journal of Magnesium and Alloys 2022年第1期10卷 160-174页

作者： Sang Kyu Woo Risheng Pei Talal Al-Samman Dietmar Letzig Sangbong Yi Magic-Magnesium Innovation Center Institute for Materials and Process DesignHelmholtz-Zentrum GeesthachtGeesthacht 21502Germany Institut für Metallkunde und materialphysik RWTH Aachen UniversityAachen 52056Germany

Even though Mg alloys containing Mn and rare earth elements lead to higher ductility and lower yield asymmetry due to the weak texture after extrusion, plastic instability, commonly known as the Portevin–Le Chatelier(PLC) effect, causes unexpected fragility in the service environment. In the present study, the PLC phenomenon and texture development during the deformation of Mg-Mn and Mg-Mn-Nd extruded alloys were investigated under various temperatures and strain rates. The addition of Nd causes not only texture weakening but also severe PLC phenomenon. The PLC phenomenon was significantly affected by the temperatures and the strain rates, which causes a difference in mechanical properties and development of texture. In the conditions of high temperature and low strain rate, the strength increased while the elongation decreased significantly, and obvious PLC phenomenon with severe serration and negative strain rate sensitivity. The initial texture was maintained even after deformation only under severe PLC conditions, and this is due to the restriction of basal slip and suppression of lattice rotation in PLC conditions. The series of results indicate that the PLC phenomenon causes a reduction of formability even at high temperature.

关键词： Magnesium Plastic instability Portevin–Le Chatelier effect Manganese Neodymium Texture

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Application of cold drawn lamellar microstructure for developing ultra-high strength wires

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中国有色金属学会会刊：英文版 2007年第6期17卷 1129-1138页

作者： S. Goto R. Kirchheim T . Al-Kassab C. Borchers Faculty of Engineering and Resource Science Akita University Tegata Gakuencho Akita 010-8502 Japan institute fuer materialphysik University of Goettingen Friedrich-Hund-Platz 1 D-37077 Goettingen Germany

Composite materials having lamellar structure are known to have a good combination of high strength and ductility. They are widely used in the fields of automobiles, civil engineering and construction, machines and many other industries. An application of lamellar microstructure for developing ultra-high strength steel wires was studied and discussed. Based on the experimental results, the relationships between the strength increase and microstructure development during the cold wire drawing were studied to reveal the strengthening mechanism. As cold drawing proceeds, the wire strength extremely increases, the microstructure changes from large single crystal lamellar structure to very fine polycrystalline lamellar one which has nano-sized grains, high dislocation density and amorphous regions. From the results obtained, it is concluded that heavy cold drawing technique is an effective method for lamellar composite to get high strength wires. Furthermore, formation process of the best microstructure for producing the ultra-high strength wires was also discussed.

关键词：薄片复合物金属丝加固装置机械性质

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Solute drag-controlled grain growth in magnesium investigated by quasi in-situ orientation mapping and level-set simulations

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镁合金学报(英文) 2023年第7期11卷 2312-2325页

作者： Risheng Pei Yujun Zhao Muhammad Zubair Sangbong Yi Talal Al-Samman Institut für Metallkunde und materialphysik RWTH Aachen University52056 AachenGermany institute of Materials and Process Design Helmholtz-Zentrum Hereon21502 GeesthachtGermany Department of Metallurgical and Materials Engineering Faculty of ChemicalMetallurgical&Polymer EngineeringUniversity of Engineering&Technology(UET)LahorePakistan institute for Materials Ruhr-Universität Bochum44801 BochumGermany

Critical properties of metallic materials,such as the yield stress,corrosion resistance and ductility depend on the microstructure and its grain size and size *** atoms that favorably segregate to grain boundaries produce a pinning atmosphere that exerts a drag pressure on the boundary motion,which strongly affects the grain growth behavior during *** the current work,the characteristics of grain growth in an annealed Mg-1 wt.%Mn-1 wt.%Nd magnesium alloy were investigated by advanced experimental and modeling *** quasi in-situ orientation mappings with a scanning electron microscope were performed to track the evolution of local and global microstructural characteristics as a function of annealing *** segregation at targeted grain boundaries was measured using three-dimensional atom probe ***-set computer simulations were carried with different setups of driving forces to explore their contribution to the microstructure development with and without solute *** results showed that the favorable growth advantage for some grains leading to a transient stage of abnormal grain growth is controlled by several drivers with varying importance at different stages of *** longer annealing times,residual dislocation density gradients between large and smaller grains are no longer important,which leads to microstructure stability due to predominant solute *** fluctuations in residual dislocation energy and solute concentration near grain boundaries cause different boundary segments to migrate at different rates,which affects the average growth rate of large grains and their evolved shape.

关键词： Magnesium alloys Grain growth Quasi in-situ EBSD Level-set simulation Solute drag Dislocation density gradient

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Microstructure Evolution during Friction Stir Welding of Aluminum Alloy AA2219

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Journal of Materials Science & Technology 2010年第8期26卷 747-753页

作者： K.S.Arora S.Pandey M.Schaper R.Kumar Mechanical Engineering Department Indian Institute of Technology Institut fuer Werkstoffwissenschaft Technische Universitaet Dresden Institut fuer Sicherheitsforschung Forschungszentrum Dresden-Rossendorf Engineering Division National Metallurgical Laboratory

The characterization of microstructure evolution in friction stir welded aluminum alloy was carried out by optical microscopy （OM） and transmission electron microscopy （TEM） and electron backscatter diffraction （EBSD）. The weld nugget consisted of very fine equiaxed grains and experienced dissolution of nearly half of metastable precipitates into the matrix during welding. Thermomechanically affected zone （TMAZ） also experienced dissolution of precipitates but to a lesser extent whereas coarsening of precipitates was observed in heat affected zone （HAZ）. Grain boundary misorientation measurements using EBSD indicated continuous dynamic recrystallization as the underlying mechanism for the fine equiaxed nugget grains. The yield and tensile strength of the weld decreased with comparison to base material. But due to the decrease of grain size and the dissolution of second phase precipitates, an increased Charpy energy value was observed in the weld n u gget.

关键词： Friction stir welding AA2219 Precipitates Vickers hardness Tensile testing Charpy impact energy

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Experiments on Gas Jet in the Wendelstein 7-AS Stellarator

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Plasma Science and Technology 2003年第5期5卷 1933-1938页

作者：姚良骅 J.Baldzuhn Southwestern institute of Physics Chengdu 610041China Max-Planck Institut fuer Plasma physik EURATOM Ass.17491 GreifswaldGermany

Wendelstein 7-AS (W7-AS) pertains to an advanced helical stellarator. A new fuelling method, the supersonic molecular beam injection (SMBI, named Gas Jet in Germany) system was installed in W7-AS in May 2001 as a cooperation research item co-supported by the National Nature Science Foundation of China and the Max-Planck institute of Plasma Physics, Garching, Germany. The experiments of the gas jet with hydrogen or deuterium on W7-AS were implemented. The experimental results exhibit the following features such as high fuelling efficiency, stable high-density plasmas and reduction of the recycling fluxes from the vessel wall during injection. These crucial points show that the new fuelling method can be applied to long and stable discharges.

关键词： gas jet (Supersonic Molecular Beam) injection wendelstein 7-AS stellarator fuelling

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微重力环境下二元复杂等离子体界面上的密度波研究

微重力环境下二元复杂等离子体界面上的密度波研究

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第十八届全国等离子体科学技术会议

作者：杜诚然杨利张菁 Mierk Schwabe Sergey Zhdanov Hubertus Thomas 东华大学理学院 Institut fuer materialphysik im Weltraum Deutsches Zentrum fuer Luft-und Raumfahrt (DLR)

在弱电离气体中加入两种大小不同的颗粒可以形成二元复杂等离子体。颗粒由于体积不同,在与等离子体发生相互作用时的带电量也不同,在一定条件下,两种颗粒会发生相分离。实验发现,在微重力环境下,即使亚稳态相分离的条件没有达到,由于等... 详细信息

在弱电离气体中加入两种大小不同的颗粒可以形成二元复杂等离子体。颗粒由于体积不同,在与等离子体发生相互作用时的带电量也不同,在一定条件下,两种颗粒会发生相分离。实验发现,在微重力环境下,即使亚稳态相分离的条件没有达到,由于等离子体放电腔内存在定向的离子流,两种颗粒也会自发的分离开来,形成两个相对独立的颗粒云,并在其接触部分形成一个界面。在复杂等离子体中,密度波有多种激发方式,包括利用外界调制电场激发、光场激发、由Heartbeat不稳定性激发、以及由于双流不稳定性导致的自激发。利用激光微摄技术,密度波传播的动力学过程可以被记录下来。本报告介绍了国际空间站微重力复杂等离子体实验室PK 3-Plus中进行的一系列二元复杂等离子体界面上的密度波研究。在大颗粒云中,波动由双流不稳定性自激发产生,在小颗粒云中,密度波由heartbeat不稳定性诱发。波动的频率和波长与所在位置的颗粒尺寸、带电量以及颗粒密度、所在位置的电场强度都有关联。我们在实验中首次发现密度波在界面传播的前后存在一个"碰撞区"和"融合区"。这项工作为研究两种不同介质界面上的波动与波动相互作用提供了一个宏观的图像。

关键词：复杂等离子体自激发波

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Propagating disturbances along fan-like coronal loops in an active region

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Research in Astronomy and Astrophysics 2015年第11期15卷 1832-1842页

作者： Sudip Mandal Tanmoy Samanta Dipankar Banerjee S.Krishna Prasad Luca Teriaca Indian institute of Astrophysics Astrophysics Research Centre School of Mathematics and Physics Queen’s University Belfast Max-Planck-Institut fuer Sonnensystemforschung (MPS)

Propagating disturbances are often observed in active region fan-like coronal loops. They were thought to be due to slow mode magnetohydrodynamic waves based on some of the observed properties. However, recent studies involving spectroscopy indicate that they could be due to high speed quasi-periodic upflows which are difficult to distinguish from upward propagating slow waves. In this context, we have studied a fan loop structure in the active region AR 11465 using simultaneous spectroscopic and imaging observations from the Extreme Ultraviolet Imaging Spectrometer onboard Hinode and Atmospheric Imaging Assembly onboard Solar Dynamics Observatory. Analysis of the data shows significant oscillations at different locations. We explore the variations in different line parameters to determine whether the waves or flows could cause these oscillations to improve the current understanding of the nature of these disturbances.

关键词： wavelet simultaneous distinguish Extreme propagating Solar fitting pixel spectroscopic Roberts

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Experimental and numerical study on energy dissipation in freely cooling granular gases under microgravity

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Chinese Physics B 2018年第8期27卷 324-330页

作者：王文广厚美瑛陈科虞培东 Matthias Sperl Key Laboratory of Soft Matter Physics Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of Sciences School of Physical Sciences University of Chinese Academy of Sciences Institut für materialphysik im Weltraum Deutsches Zentrum für Luft-und Raumfahrt

Energy dissipation is one of the most important properties of granular gas, which makes Its behavior dltterent trom that of molecular gas. In this work we report our investigations on the freely-cooling evolution of granular gas under microgravity in a drop tower experiment, and also conduct the molecular dynamics （MD） simulation for comparison. While our experimental and simulation results support Haff＇s law that the kinetic energy dissipates with time t as E（t）（1 ＋ t/v） 2, we modify ~＂ by taking into account the friction dissipation during collisions, and study the effects of number density and particle size on the collision frequency. From the standard deviation of the measured velocity distributions we also verify the energy dissipation law, which is in agreement with Haff＇s kinetic energy dissipation.

关键词： granular gas freely coolin microgravity

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APPROXIMATE CALCULATION OF SOLAR RADIATION TRANSFER IN CLEAR ATMOSPHERE

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Chinese Science Bulletin 1989年第11期34卷 930-932页

作者：赵高祥汪宏七 B.ROCKEL E.RASCHKE institute of Atmospheric Physics Academia Sinica Beijing Institut fuer Geophysik und Meteorologic der Universitaet zu Koeln

Bsaed on two-stream approximation, the upward and downward diffuse solar radiation flux densities, M_i^+ and M_i^-, in a plane-parallel atmosphere can be expressed

关键词： solar radiation atmosphere diffuse radiation.

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