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Revealing the Diversity of dendritic morphology Evolution During Solidification of Magnesium Alloys using Synchrotron X-ray Imaging:A Review

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Acta Metallurgica Sinica(English Letters) 2022年第2期35卷 177-200页

作者： Yanan Wang Sansan Shuai Chenglin Huang Tao Jing Chaoyue Chen Tao Hu Jiang Wang Zhongming Ren State Key Laboratory of Advanced Special Steels School of Materials Science and EngineeringShanghai UniversityShanghai 200444China School of Materials Tsinghua UniversityBeijing 10084China

In this paper,the diversity of complicated dendrite microstructure and its evolution behavior during solidification in different magnesium alloys under various processing conditions were illustrated using synchrotron X-ray imaging technique.A variety of dendritic morphologies and branching structures were revealed,i.e.,sixfold plate-like symmetric structure in Mg-Al-based structure,12-branch structure in Mg-Zn-based alloys and 18-branch structure in Mg-Sn-and Mg-Ca-based alloys as well as seaweed like hyper-branched structure in Mg-38wt%Zn *** addition,a dendrite morphology and orientation transition with increasing addition of Zn content were also observed in Mg-Zn alloy,with dendrite growth pattern transform from anisotropy(low Zn addition)with sixfold symmetric snow-flake structure to relative isotropy(intermediate Zn addition)where seaweed morphology presented and then back to anisotropy(high Zn addition)when only 12 branches with preferredorientations were *** phase-field model representing the typical dendritic morphologies and branching structures under various conditions was also depicted and ***,the two-dimensional(2D)real-time dendrite growth dynamics in different Mg-based alloys captured using synchrotron X-ray radiography for unveiling the originate of theα-Mg dendrite was *** this,the four-dimensional(3D+time)synchrotron X-ray tomographic in situ observation of dendritic morphology evolution indicating the formation mechanism of the diverse dendritic morphology during Mg-Sn-and Mg-Zn-based alloys was also ***,the future study on exploring the complicated dendritic morphologies and their origination during solidification of Mg-based alloys is prospected.

关键词： Magnesium alloys Solidification microstructure dendritic morphology Synchrotron X-ray imaging Growth pattern

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A Modified Cellular Automaton Method for the Modeling of the dendritic morphology of Binary Alloys

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Tsinghua Science and Technology 2006年第5期11卷 495-500页

作者：刘影许庆彦柳百成 Department of Mechanical Engineering Tsinghua University

A cellular automaton （CA）-based model for the precise two-dimensional simulation of the dendritic morphology of cast aluminum alloys was developed. Compared with previous CA models, the new model considers the solidification process in more detail, solving the solute and heat conservation equations in the modeling domain, including calculation of the solid fraction, the tip velocity, and the solute diffusion process, all of which have significant influence on the dendrite evolution. The rotating grids technique was used in the simulation to avoid anisotropy introduced by the square grid. dendritic grain profiles for different crystallographic orientations show the existence of a great number of regular and parallel secondary and tertiary arms. The simulation results for the secondary arm spacing and grain size were compared with experimental data and with results reported in the literature. A good agreement was found between the simulated results and the experimental data. It can be concluded that the model can be used to predict the dendritic microstructure of aluminum alloy in a quantitative manner.

关键词： Al alloy dendritic morphology modified cellular automaton grain size secondary arm spacing

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Influence of periodic pressure on dendritic morphology and sidebranching

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China Foundry 2020年第4期17卷 279-285页

作者： Shan Shang Zhi-peng Guo Zhi-qiang Han Xin-yu Zhang Yi-nuo Cheng Jun Li State Key Laboratory of Automotive Safety and Energy Tsinghua UniversityBeijing 100084China School of Vehicle and Mobility Tsinghua UniversityBeijing 100084China School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China HiRain Technologies Co. Ltd.Beijing 100191China

The influence of periodic pressure with low and high frequencies on microstructure and dendritic sidebranching was studied by using 3-D phase field method. In both low and high frequency cases, the variation trend of SDAS (secondary dendritic arm spacing) with increasing pressure frequency is opposite to that of sidebranching frequency, while the variation trend of the average length of secondary arms is consistent with that of sidebranching frequency. The high sidebranching frequency indicates that more secondary arms share the whole driving force of dendrite growth, resulting in lower driving force for each one and leading to less developed secondary arms. The smallest SDAS is obtained when perturbed by the periodic pressure with the frequency of 0.157/τ0 (τ0 is the physical unit of time in the dimensionless phase field model) and 2.200/τ0 in low and high frequency cases, respectively. Comparisons of dendritic morphology and secondary arms are made between the low and high frequency cases. Firstly, in the low frequency case, secondary arms are luxuriant especially when pressure frequency is low, with many high-order side branches stretching out. Secondly, the average length of secondary arms in primary dendrite is longer in the low frequency case than that without pressure, and much longer than that in the high frequency case. Thirdly, the dendrite tip without side branches in the high frequency case is much longer than that in the low frequency case. All of the differences in dendritic morphology and sidebranching in the two cases can be attributed to the different modulation mechanism. In the low frequency case, periodic pressure determines tip velocity and then modulates sidebranching directly. While in the high frequency case, periodic pressure cannot determine sidebranching directly, but via modulating tiny protuberances in dendrite tip, part of which evolves into side branch. In this case, the tiny protuberances take part of the whole driving force, leading

关键词： periodic pressure dendritic morphology SDAS phase field method

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Exercise promotes recovery after motoneuron injury via hormonal mechanisms

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Neural Regeneration Research 2020年第8期15卷 1373-1376页

作者： Cory Chew Dale R.Sengelaub Psychological and Brain Sciences Indiana University

Injuries to spinal motoneurons manifest in a variety of forms,including damage to peripheral axons,neurodegenerative disease,or direct insult *** injuries produce a variety of negative structural and functional changes in both the directly affected and neighboring *** is a relatively simple behavioral intervention that has been demonstrated to protect against,and accelerate recovery from,these negative *** this article,we describe how exercise is neuroprotective for motoneurons,accelerating axon regeneration following axotomy and attenuating dendritic atrophy following the death of neighboring *** both of these injury models,the positive effects of exercise have been found to be dependent on gonadal hormone *** we describe a model in which exercise,hormones,and brain-derived neurotrophic factor might all interact to produce neuroprotective effects on motoneuron structure following neural injury.

关键词： axon regeneration axotomy dendritic morphology exercise hormones neuroprotection neurotrophins

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Phase-field numerical simulation of three-dimensional competitive growth of dendrites in a binary alloy

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中国铸造：英文版 2018年第1期15卷 44-50页

作者： Li Feng Ya-long Gao Chang-sheng Zhu Guo-sheng An Xin Deng Bei-bei Jia School of Materials and Engineering Lanzhou University of Technology State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals Lanzhou University of Technology School of Computer and Communication Lanzhou University of Technology

The normal vector of migration direction in the solid-liquid interface of dendrites was used to describe the phase-field governing equation. By using the three angles formed by the normal vector for the migration direction of the dendritic growth interface and the coordinate axes of the simulation region, the authors expressed the interfacial anisotropy equation, and built a phase-field model for the competitive growth of multiple grains. Taking a Al-2%mole-Cu binary alloy as an example, the competitive growth of multiple grains during isothermal solidification was simulated by applying parallel computing techniques. In addition, the phase field simulation results were verified by the experimental method. The simulation results show that the competitive growth of equiaxed dendrite is divided into two types: the first occurs during the process of competitive growth, the tips of primary dendrite on different grains taking part in the competition stop growing in their optimal growth direction; the second also occurs during competitive growth, the tips of primary dendrite which participate in the competition on different grains never stop growing in their optimal growth direction. The dendritic morphologies of the first competition growth type are divided into two types. Primary dendrites of grains taking part in the competition stop growing in their optimal growth direction and the competition plane enlarges when neither one wins the competition. However, when one wins the competition, the primary dendrites of grains with superiority go through the blocking grains and continue to grow in their optimal growth direction. The primary dendrites of inferior grains stop growing in their optimal growth direction and then instead grow in those areas without obstacles. The dendritic morphology of the second competition-growth type is shown to be the deformation of primary dendrites, which are mainly represented as the deflection and bending observed from different views. Compar

关键词： dendrite Al-Cu binary alloy competitive growth dendritic morphology

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Histone H3K27me3 demethylase Utx regulates neuronal development and cognition

Histone H3K27me3 demethylase Utx regulates neuronal developm...

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中国神经科学学会第十二届全国学术会议

作者： Gang-Bin Tang Yu-Qiang Zeng Pei-Pei Liu Ting-Wei Mi Shuang-Feng Zhang Shang-Kun Dai Qing-Yuan Tang Lin Yang Ya-Jie Xu Hai-Liang Yan Hong-Zhen Du Zhao-Qian Teng Feng-Quan Zhou Chang-Mei Liu State Key Laboratory of Stem Cell and Reproductive Biology Institute of Zoology Chinese Academy of Sciences Savaid Medical School University of Chinese Academy of Sciences School of Life Sciences University of Science and Technology of China The State Key Laboratory of Integrated Management of Pest Insects and Rodents Institute of Zoology Chinese Academy of Sciences Department of Orthopaedic Surgery The Johns Hopkins University School of Medicine The Solomon H. Snyder Department of Neuroscience The Johns Hopkins University School of Medicine

Histone demethylase Utx（ubiquitously transcribed tetratricopeptide repeat gene on X chromosome） mediates removal of repressive trimethylation of histone H3 lysine 27（H3K27me3） to establish a mechanistic switch to activate large sets of genes in many systems. However, its biological function in the brain is largely unknown. Here, we show that deletion of Utx results in increased anxiety-like behaviors and impaired spatial learning and memory in mice. Loss of Utx in the hippocampus leads to reduced long-term potentiation（LTP） and amplitude of miniature excitatory postsynaptic current（m EPSC）, aberrant dendrite development and defective synapse formation. Transcriptional profiling reveals that Utx regulates a subset of genes which are involved in the regulation of dendritic morphology, synaptic transmission, mood and cognition. Taken together, our data demonstrate that Utx has critical roles in mediating neural and behavioral plasticity in mice.

关键词： Utx H3K27me3 dendritic morphology cognition

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