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Influence of Al/Cu content on grain boundary diffusion in Nd-Fe-B magnet via in-situ observation

Journal of Rare Earths 2019年第4期37卷 398-403页

作者： Xinghua Cheng Jian Li Lei Zhou Tao Liu Xiaojun Yu Bo Li China Iron & Steel Research Institute Croup Functional Materials Division Advanced Technology & Materials Co. Ltd.

The influence of aluminum and copper content in the starting Nd-Fe-B magnet on grain boundary diffusion process(GBDP) was studied by observing the phase transformation behaviors of the magnets in-situ at high temperature. A higher coercivity increment is discovered in the sample with higher AI/Cu despite the fact that its Dy diffusion amount is the same as the other. DSC analysis shows an evident melting behavior in the higher Al/Cu sample. Laser scanning confocal microscopy(LSCM) in-situ characterization shows a large amount of melted intergranular phase spills out to the surface simultaneously at around 600 ℃ in the high Al/Cu sample, while the phase spills out gradually one after another in the range between 623 and680 ℃ in the other sample, which indicates that the intergranular phase can be more easily melted in the sample containing more AI/Cu. The area fraction of matrix phase remarkably shrinks while that of intergranular phase enlarges after LSCM heating, which demonstrates the outer region of the Nd_2 Fe_(14)B grains melt at the temperature of 900 ℃. Electron probe microanalyzer result(EPMA) shows that the Nd and Dy concentrate in edge regions and subsequently mix into the intergranular phase with the melting of the grain edge, while a large amount of AI and Cu in the intergranular phase spill out. Nevertheless, the sample with higher starting AI/Cu still remains higher residual contents after LSCM experiments, and that could probably be the main reason why the high AI/Cu magnet shows smaller coercivity decrement after LSCM experiment. Overall, the increase of AI/Cu in the starting magnet optimizes the Dy distribution and the wettability of intergranular phase, enhancing coercivity increment effect further.

关键词： Nd-Fe-B sintered magnet Grain boundary diffusion process In-situ LSCM Melting behavior Copper Aluminum

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SpinNet: Spinning convolutional network for lane boundary detection

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Computational Visual Media 2019年第4期5卷 417-428页

作者： Ruochen Fan Xuanrun Wang Qibin Hou Hanchao Liu Tai-Jiang Mu Tsinghua University Beijing100084China Nankai University Tianjin300350China

In this paper,we propose a simple but effective framework for lane boundary detection,called Spin *** that cars or pedestrians often occlude lane boundaries and that the local features of lane boundaries are not distinctive,therefore,analyzing and collecting global context information is crucial for lane boundary *** this end,we design a novel spinning convolution layer and a brand-new lane parameterization branch in our network to detect lane boundaries from a global *** extract features in narrow strip-shaped fields,we adopt stripshaped convolutions with kernels which have 1×n or n×1 shape in the spinning convolution *** tackle the problem of that straight strip-shaped convolutions are only able to extract features in vertical or horizontal directions,we introduce the concept of feature map rotation to allow the convolutions to be applied in multiple directions so that more information can be collected concerning a whole lane ***,unlike most existing lane boundary detectors,which extract lane boundaries from segmentation masks,our lane boundary parameterization branch predicts a curve expression for the lane boundary for each pixel in the output feature *** the network utilizes this information to predict the weights of the curve,to better form the final lane *** framework is easy to implement and end-to-end *** show that our proposed Spin Net outperforms state-of-the-art methods.

关键词： object detection lane boundary detection autonomous driving deep learning

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Effects of initial grain size and strain on grain boundary engineering of high-nitrogen CrMn austenitic stainless steel

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International Journal of Minerals,Metallurgy and Materials 2018年第8期25卷 922-929页

作者： Zhen-hua Wang Jian-jun Qi Wan-tang Fu School of Mechanical Engineering Yanshan UniversityQinhuangdao 066004China State Key Laboratory of Metastable Materials Science and Technology Yanshan UniversityQinhuangdao 066004China HBIS Group Technology Research Institute Shijiazhuang 050023China

18 Mn18 Cr0.5 N steel with an initial grain size of 28–177 μm was processed by 2.5%–20% cold rolling and annealing at 1000°C for 24 h,and the grain boundary character distribution was examined via electron backscatter *** strain(2.5%) favored the formation of low-Σ *** this strain,the fraction of low-Σ boundaries was insensitive to the initial grain ***,specimens with fine initial grains showed decreasing grain size after grain boundary engineering *** fraction of low-Σ boundaries and the(Σ9 + Σ27)/Σ3 value decreased with increasing strain; furthermore,the specimens with fine initial grain size were sensitive to the ***,the effects of the initial grain size and strain on the grain boundary engineering were discussed in detail.

关键词： grain boundary engineering grain boundary character distribution grain size strain austenitic stainless steel

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Grain boundary and microstructure engineering of Inconel 690 cladding on stainless-steel 316L using electron-beam powder bed fusion additive manufacturing

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Journal of Materials Science & Technology 2019年第2期35卷 351-367页

作者： I.A.Segura L.E.Murr C.A.Terrazas D.Bermudez J.Mireles V.S.V.Injeti K.Li B.Yu R.D.K.Misra R.B.Wicker W.M.Keck Center for 3D Innovation The University of Texas at El Paso Department of Mechanical Engineering The University of Texas at El Paso Department of Metallurgical Materials and Biomedical Engineering The University of Texas at El Paso

This research explores the prospect of fabricating a face-centered cubic(fcc) Ni-base alloy cladding(Inconel 690) on an fcc Fe-base alloy(316 L stainless-steel) having improved mechanical properties and reduced sensitivity to corrosion through grain boundary and microstructure engineering concepts enabled by additive manufacturing(AM) utilizing electron-beam powder bed fusion(EPBF). The unique solidification and associated constitutional supercooling phenomena characteristic of EPBF promotes[100] textured and extended columnar grains having lower energy grain boundaries as opposed to random, high-angle grain boundaries, but no coherent {111} twin boundaries characteristic of conventional thermo-mechanically processed fcc metals and alloys, including Inconel 690 and 316 L *** addition to [100] textured grains, columnar grains were produced by EPBF fabrication of Inconel 690 claddings on 316 L stainless-steel substrates. Also, irregular 2–3 μm diameter, low energy subgrains were formed along with dislocation densities varying from 108 to 109 cm^2, and a homogeneous distribution of Cr_(23)C_6 precipitates. Precipitates were formed within the grains(with ~3 μm interparticle spacing),but not in the subgrain or columnar grain boundaries. These inclusive, hierarchical microstructures produced a tensile yield strength of 0.527 GPa, elongation of 21%, and Vickers microindentation hardness of 2.33 GPa for the Inconel 690 cladding in contrast to a tensile yield strength of 0.327 GPa, elongation of 53%, and Vickers microindentation hardness of 1.78 GPa, respectively for the wrought 316 L stainlesssteel substrate. Aging of both the Inconel 690 cladding and the 316 L stainless-steel substrate at 685?C for50 h precipitated Cr_(23)C_6 carbides in the Inconel 690 columnar grain boundaries, but not in the low-angle(and low energy) subgrain boundaries. In contrast, Cr_(23)C_6 carbides precipitated in the 316 L stainless-steel grain boundaries, but not in the low energy

关键词： Additive manufacturing Electron-beam powder bed fusion (EPBF) Inconel 690 cladding 316L stainless steel Grain boundary engineering Materials characterization Mechanical properties

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Anomalous boundary deformation induced by enclosed active particles

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Chinese Physics B 2017年第10期26卷 82-88页

作者：田文得顾燕郭永坤陈康 Center for Soft Condensed Matter Physics & Interdisciplinary Research College of Physics Optoelectronics and EnergySoochow University Kavli Institute for Theoretical Physics China Chinese Academy of Sciences

We simulate a two-dimensional model of a round soft boundary enclosed with self-propelled particles. Persistent motion drives these particles to accumulate near the boundary, thereby dramatically deforming the boundary shape through collisions. Quantitative analyses of the boundary shape and the particle distribution show that there are two typical regimes in the variation of the morphology with the increase of self-propulsion of particles. One is under small forces, characterized by the radially inhomogeneous distribution of particles and the suppression of local fluctuations of the almost round boundary, and the other is under large forces, featured by the angularly inhomogeneous distribution of particles and the global shape deformation of the boundary. These two features are strongly cooperative. We also find different mechanisms in the particle relocation at low and high particle concentrations.

关键词： self-propelled particles boundary active matter confinement

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Grain boundary restructuring and La/Ce/Y application in Nd–Fe–B magnets

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Chinese Physics B 2019年第7期28卷 25-53页

作者： Mi Yan Jiaying Jin Tianyu Ma School of Materials Science and Engineering State Key Laboratory of Silicon MaterialsKey Laboratory of Novel Materials for Information Technology of Zhejiang Province Zhejiang University

Since the 1980 s, Nd–Fe–B with largest energy product(BH)max approaching the theoretical limit has become the landmark of permanent magnetic *** application spectrum for Nd–Fe–B continues to expand over time both in the industrial and commercial sectors, which leads to growing research interests for solving the long-standing drawbacks of Nd–Fe–B, i.e., poor corrosion resistance, low coercivity, high Dy/Tb and low La/Ce/Y *** the above obstacles, we aim to present the novel grain boundary restructuring(GBR) approach, from GB design, processing, to structure evolution and property evaluation with a focus on the corrosion and coercivity mechanism of the restructured 2:14:1-typed *** with an introduction to the fundamental of GBR, two representative examples,high-electrode-potential(Pr, Nd)32.5Fe62.0Cu5.5 and low-melting-point Dy71.5Fe28.5, are given with detailed descriptions of the advantages of GBR to enhance the intrinsic anti-corrosion stability and to strengthen the coercivity at low Dy ***–property correlations are established to understand the critical importance of regulating the restructured GB phase to maximize the all-round performance of the 2:14:1-typed permanent *** at sustainable and balanced development of rare earth(RE) industry, the proceeding section proposes new prototypes of La–Ce and Y–Ce co-substitutions with dual benefits of stabilizing the 2:14:1 tetragonal phase and strengthening the intrinsic hard *** findings of additional REFe2 intergranular phase delight that the GBR approach also opens up a new horizon of research and application to develop high-performance La/Ce/Y-rich permanent magnets with deliberately tailored GB phase.

关键词： grain boundary restructuring coercivity corrosion resistance Dy/Tb La/Ce/Y

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Scaled boundary finite element method with exact defining curves for two-dimensional linear multi-field media

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Frontiers of Structural and Civil Engineering 2019年第1期13卷 201-214页

作者： Jaroon RUNGAMORNRAT Chung Nguyen VAN Applied Mechanics and Structures Research Unit Department of Civil EngineeringFaculty of EngineeringChulalongkorn UniversityBangkok 10330Thailand Faculty of Civil Engineering Ho Chi Minh City of Technology and EducationHo Chi Minh 721400Vietnam

This paper presents an efficient and accurate numerical technique based upon the scaled boundary finite element method for the analysis of two-dimensional,linear,second-order,boundary value problems with a domain completely described by a circular defining *** scaled boundary finite element formulation is established in a general framework allowing single-field and multi-field problems,bounded and unbounded bodies,distributed body source,*** boundary conditions to be treated in a unified *** conventional polar coordinates together with a properly selected scaling center are utilized to achieve the exact description of the circular defining curve,exact geometry of the domain,and exact spatial differential *** finite element shape functions are employed in the discretization of both trial and test functions in the circumferential direction and the resulting eigenproblem is solved by a selected efficient *** computational performance of the implemented procedure is then fully investigated for various scenarios to demonstrate the accuracy in comparison with standard linear elements.

关键词： multi-field problems defining curve exact geometry general boundary conditions SBFEM

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A fast algorithm for calculating surface electric field of converter valve shield system by multipole boundary element method

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Science China(Technological Sciences) 2018年第11期61卷 1745-1754页

作者： SHI YuXin WANG ZeZhong Beijing Key Laboratory of High Voltage & EMC North China Electric Power University

The surface electric field analysis of the converter valve shield system is a large-scale electrostatic field problem, which is difficult to analyse. The fast multipole boundary element method(FMBEM), which is suitable for solving large-scale problems,can accelerate the computation speed and conserve memory. However, the coefficient matrix implicitly formed by using the FMBEM is sometimes ill-conditioned, especially for large-scale problems; thus, the convergence of iteration is poor. In this paper, a fast solver is proposed to improve efficiency. First, an adaptive GMRES(m) with variant restart parameter is adjusted for the Galerkin FMBEM. In addition, the sparse approximate inverse preconditioner is improved, and a new sparsity pattern is proposed for the multiscale problem derived from the converter valve shield system. The numerical results show that the accuracy can meet the engineering requirements compared with the finite element method. Compared with other solvers and preconditioners, the algorithm can achieve a satisfactory convergence rate and reduce the computation time. In addition, a single bridge shield system of ±160 kV converter valve is successfully analysed using the proposed method.

关键词： converter valve electrostatic field fast multipole boundary element method (FMBEM) GMRES preconditioner

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Reduction of turbulent boundary layer drag through dielectric-barrier-discharge plasma actuation based on the Spalding formula

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Plasma Science and Technology 2019年第4期21卷 107-114页

作者： Bin WU Chao GAO Feng LIU Ming XUE Yushuai WANG Borui ZHENG Northwestern Polytechnical University Xi'an 710072.People's Republic of China University of California IrvineCA.92697-3975United States of America Xi'an University of Technology Xi'an 710048.People's Republic of China

It is a very difficult task to develop a method of reducing turbulent boundary layer ***,in recent years,plasma flow control technology has demonstrated huge potential in friction drag *** further investigate this issue,a smooth plate model was designed as a testing object arranged with a bidirectional dielectric-barrier-discharge(DBD)plasma *** addition,measurement of skin friction drag was achieved by applying hot wire anemometry to obtain the velocity distribution of the turbulent boundary layer.A method of quantifying the friction drag effect was adopted based on the Spalding formula fitted with the experiment *** plasma actuation was conducted,a velocity defect occurred at the two measuring positions,compared with the no plasma control condition;this means that the DBD plasma actuation could reduce the drag successfully in the downstream of the ***,drag reduction caused by backward actuation was slightly more efficient than that caused by forward *** an increasing distance from plasma actuation,the drag-reduction effect could become *** results also show that the improvement of drag-reduction efficiency using a DBD plasma actuator can achieve about 8.78%in the local region of the experimental flat model.

关键词： DBD plasma actuator flow control Spalding formula drag reduction turbulent boundary layer

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Numerical simulation of the influence of aerosol radiation effect on urban boundary layer

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Science China Earth Sciences 2018年第12期61卷 1844-1858页

作者： Xinran WANG Xiaodong HE Shiguang MIAO Youjun DOU China Institute of Atomic Energy Beo'ing 102413China Institute of Urban Meteorology China Meteorological AdministrationBeijing 100089China

With the intensification of pollution and urbanization, the aerosol radiation effect continues to play an important role in the urban boundary layer. In this paper, a winter pollution process in Beijing has been taken as an example, and a new aerosol vertical profile in the radiative parameterization scheme within the Weather Forecast Research and Forecasting(WRF) model has been updated to study the effect of aerosols on radiation and the boundary layer. Furthermore, the interactions among aerosols,urbanization, and planetary boundary layer(PBL) meteorology were discussed through a series of numerical experiments. The results show the following:(1) The optimization improves the performance of the model in simulating the distribution features of air temperature, humidity, and wind in Beijing.(2) The aerosols reduce the surface temperature by reducing solar radiation and increasing the temperature in the upper layer by absorbing or backscattering solar radiation. The changes in the PBL temperature lead to more stable atmospheric stratification, reducing the energy transfer from the surface and the height of the boundary layer.(3) With the increase in the aerosol optical depth, the atmospheric stratification most likely becomes stable over rural areas, most likely becomes stable over suburb areas, and has great difficultly becoming stable over urban areas. Aerosol radiative forcing,underlying urban surfaces, and the interaction between them are the main factors that affect the changes in the meteorological elements in the PBL.

关键词： Aerosol Urbanization boundary layer Meteorological elements WRF

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