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nanotwin-assisted nitridation of quenched FeNi alloy nanopowders for rare-earth-free magnets

Journal of Materials Science & Technology 2023年第34期165卷 244-252页

作者： Jian Wang Yusuke Hirayama Kazuyuki Suzuki Kwangjae Park Zheng Liu Kenta Takagi Kimihiro Ozaki Innovative Functional Materials Research Institute National Institute of Advanced Industrial Science and Technology4-205SakurazakaMoriyamaNagoya463-8560Japan

L1_(0)-ordered FeNi alloy with a high uniaxial magnetic anisotropy and large magnetic moment is a promising candidate for rare-earth-free permanent magnets ***,the synthesis of this chemically ordered phase remains a longstanding challenge because of its low chemical order-disorder transition temperature(200-320℃).Although a non-equilibrium synthetic route based on a nitrogen topotactic reaction has been proposed as a valid approach,the volume fraction and degree of chemical ordering of the product phase are ***,we propose a promising approach that promotes the efficient formation of L1_(0)-ordered nitride phase in FeNi nanopowders by introducing a quenching treatment during a low-oxygen induction thermal plasma *** quenched FeNi nanopowders possessed much smaller powder sizes(40.4 vs 74.0 nm),exhibited higher number densities of nanotwins(39.8%vs 24.1%)and formed much larger volume fraction(33.6 wt.%vs 0.6 wt.%)of ordered phase than the unquenched ***,quenching-induced high-density nanotwins led to the dominant coverage of serrated{001}crystal facets over the surfaces of the FeNi *** unique features substantially accelerated the formation of the L1_(0)-ordered nitride phase in the FeNi nanopowders because the{001}crystallographic orientation had the highest nitrogen *** work provides not only a valid synthetic approach for mass production of the L10-ordered nitride phase in FeNi nanopowders but also novel insights into the crystal-defect-assisted nitridation of nanomaterials.

关键词： Rare-earth-free Permanent magnet FeNi Nitridation nanotwin

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Hardness-thermal stability synergy in nanograined Ni and Ni alloys:Superposition of nanotwin and low-energy columnar boundary

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Journal of Materials Science & Technology 2023年第6期137卷 123-131页

作者： F.H.Duan Y.Lin Q.Li J.H.Luan J.Lu J.Pan Y.Li Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Laboratory of Nanomaterials&Nanomechanics Department of Mechanical EngineeringCity University of Hong KongHong KongChina State Key Laboratory of Material Processing and Die&Mould Technology and School of Materials Science and Engineering Huazhong University of Science and TechnologyWuhan 430074China Department of Materials Science and Engineering City University of Hong KongHong KongChina Centre for Advanced Structural Materials Greater Bay Joint DivisionShenyang National Laboratory for Materials ScienceCity University of Hong Kong Shenzhen Research InstituteShenzhen 518057China City U-Shenzhen Futian Research Institute Shenzhen 518045China

Refining grains into nanoscale can significantly strengthen and harden metallic materials;however,nanograined metals generally exhibit low thermal stability,hindering their practical *** this work,we exploit the superposition of the contribution of nanotwins,low-angle grain boundaries,and microalloying to tailor superior combinations of high hardness and good thermal stability in Ni and Ni *** the nanotwinned Ni having a twin thickness of∼2.9 nm and grain size of 28 nm,it exhibits a hardness over 8.0 GPa and an onset coarsening temperature of 623 K,both of which are well above those of nanograined ***/Mo microalloying can further improve the onset coarsening temperature to 773 K without comprising *** analyses reveal that high hardness is achieved via strengthen-ing offered by extremely fine ***,the superior thermal stability is mainly ascribed to the low driving force for grain growth induced by the low-angle columnar boundary architecture and to the additional pinning effect on the migration of twin/columnar boundaries provided by minor Re/Mo *** present work not only reveals a family of nanotwinned metals possessing the combination of ultra-high hardness and high thermal stability but also provides a strategy for tailoring properties of metallic materials by pairing low-angle grain boundaries and twin boundaries.

关键词： nanotwin Thermal stability Hardness Low-angle grain boundary Microalloying

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Phase-field simulation of the coupled evolutions of grain and twin boundaries in nanotwinned polycrystals

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Applied Mathematics and Mechanics(English Edition) 2018年第12期39卷 1789-1804页

作者： Yuanyuan DA Yuyang LU Yong NI CAS Key Laboratory of Mechanical Behavior and Design of Materials Department of Modern Mechanics University of Science and Technology of China

nanotwinned polycrystals exhibit an excellent strength-ductility combination due to nanoscale twins and grains. However, nanotwin-assisted grain coarsening under mechanical loading reported in recent experiments may result in strength drop based on the Hall-Petch law. In this paper, a phase-field model is developed to investigate the effect of coupled evolutions of twin and grain boundaries on nanotwin-assisted grain growth. The simulation result demonstrates that there are three pathways for coupled motions of twin and grain boundaries in a bicrystal under the applied loading, dependent on the amplitude of applied loading and misorientation of the bicrystal. It reveals that a large misorientation angle and a large applied stress promote the twinning-driven grain boundary migration. The resultant twin-assisted grain coarsening is confirmed in the simulations for the microstructural evolutions in twinned and un-twinned polycrystals under a high applied stress.

关键词： nanotwin grain growth stress effect phase-field simulation

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Theoretical study of the effects of alloying elements on Cu nanotwins

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Science China(Physics,Mechanics & Astronomy) 2020年第10期63卷 81-90页

作者： Jun Hui Wenguan Liu Biao Wang Sino-French Institute of Nuclear Engineering and Technology Sun Yat-Sen UniversityZhuhai 519082China

nanotwins form in many metallic materials to improve their strength and *** this study,we thoroughly studied the alloying effects of 10 common metal and nonmetal elements on Cu nanotwins by density functional theory(DFT).We calculated the segregation energies to determine if Cu nanotwins attract both the metal and nonmetal alloying elements;these segregation energies were then decomposed to mechanical and chemical *** Cu-Sn bonds are different from other metal alloying elements,and the strong bond between Cu and the nonmetal element results in the negative values of the chemical ***,the temperature and concentration have different effects on the nanotwin formation energy of the metal and nonmetal alloying *** determined by the Generalized Stacking Fault Energy,Al and nonmetals can inhibit the migration of Cu nanotwin boundary,and the effects of Li,Mg,and Sn are *** theoretical study serves as the foundation for the engineering nanotwin structures through alloying elements,the elements that may lead to new alloy compositions and thermomechanical processes,and are important complements to the experimental research.

关键词： nanotwin alloying element density functional theory segregation energy nanotwin formation energy generalized stacking fault energy

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Nucleation of dislocations and twins in fcc nanocrystals: Dynamics of structural transformations

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Journal of Materials Science & Technology 2019年第1期35卷 201-206页

作者： Aleksandr V.Korchuganov Aleksandr N.Tyumentsev Konstantin P.Zolnikov Igor Yu.Litovchenko Dmitrij S.Kryzhevich Elazar Gutmanas Shouxin Li Zhongguang Wang Sergey G.Psakhie Institute of Strength Physics and Materials Science of Siberian Branch of Russian Academy of Sciences National Research Tomsk State University Technion–Israel Institute of Technology Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences

This paper reports on a molecular dynamics study of structural rearrangements in a copper nanocrystal during nucleation of plastic deformation under uniaxial tension. The study shows that the resulting nucleation of partial dislocations on the free surface and their glide occurs through local fcc→bcc→hcp transformations via consistent atomic displacements. We propose an atomic model for the generation of dislocations and twins based on local reversible fcc→bcc→fcc transformations, with the reverse one proceeding through an alternative system. The model gives an insight into possible causes and mechanisms of the generation of partial dislocations and mechanical twins in two and more adjacent planes of plastically deformed nanocrystals. The obtained data allow a better understanding of how plasticity is generated in nanostructured materials.

关键词： Lattice defects Dislocation nanotwin Atomic model Molecular dynamics simulations

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Improving Fatigue Properties of 316L Stainless Steel Welded Joints by Surface Spinning Strengthening

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Acta Metallurgica Sinica(English Letters) 2024年第5期37卷 840-854页

作者： Dongqiqiong Wang Qiang Wang Xiaowu Li Zhefeng Zhang Department of Materials Physics and Chemistry School of Materials Science and Engineeringand Key Laboratory for Anisotropy and Texture of Materials(Ministry of Education)Northeastern UniversityShenyang 110819China Shi-Changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China College of Light Industry Liaoning UniversityShenyang 110036China

The surface spinning strengthening(3S)mechanism and fatigue life extension mechanism of 316L stainless steel welded joint were systematically elucidated by microstructural analyses and mechanical *** indicate that surface gradient hardening layer of approximately 1 mm is formed in the base material through grain fragmentation and deformation twin strengthening,as well as in the welding zone composed of deformedδ-phases and *** fatigue strength of welded joint after 3S significantly rises by 32%(from 190 to 250 MPa),which is attributed to the effective elimination of surface geometric defects,discrete refinement ofδ-Fe phases and the appropriate improvement in the surface strength,collectively mitigating strain localization and surface fatigue damage within the gradient strengthening *** redistributed fineδ-Fe phases benefited by strong stress transfer of 3S reduce the risk of surface weak phase cracking,causing the fatigue fracture to transition from microstructure defects to crystal defects dominated by slip,further suppressing the initiation and early propagation of fatigue cracks.

关键词： 316L stainless steel Welded joint Surface spinning strengthening nanotwin Fatigue life

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Microstructure of ultrahigh carbon martensite

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Progress in Natural Science:Materials International 2018年第6期28卷 749-753页

作者： Chao Wang Yulin Chen Jingyun Han Dehai Ping Xinqing Zhao School of Materials Science and Engineering Beihang University School of Materials Science and Engineering Dalian Jiaotong University

Recent experimental investigations suggest that the martensite formed by quenching carbon steels(0.2–1.26 mass %C) are composed of twins and nanoscale ω particles in twin boundaries, rather than carbon supersaturated uniform solutions. In order to probe the microstructure of the martensite with ultrahigh carbon content, a novel strategy is employed in the present study to obtain ultrahigh carbon martensite(approximate2.1 mass %C) by quenching ductile cast iron. The microstructure of the martensite was intensively characterized by high resolution transmitting electron microscopy. It is indicated that the microstructure of the ultrahigh carbon martensites is composed of ultrafine {112} -type twins and high-density nano-scaled ω particles embedded in twin boundaries. These ω nanoparticles in twin boundaries could remarkably impede the deformation of the movement of the nanotwins in martensites, leading to poor ductility and strength of the quenched ductile cast iron. These findings not only reveal the substructures of ultrahigh carbon martensite, but also enhance the understanding of the mechanical behavior of high carbon steels and ductile cast irons.

关键词： Ultrahigh carbon martensite Ductile cast iron nanotwin ω phase

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Stress Relaxation in Nanostructured Copper:Experiments and Simulations

Stress Relaxation in Nanostructured Copper:Experiments and S...

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第十八届全国疲劳与断裂学术会议

作者： Xu-Sheng Yang Yun-Jiang Wang Tong-Yi Zhang Department of Mechanical and Aerospace Engineering The Hong Kong University of Science and Technology State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of Sciences Shanghai University Materials Genome Institute and Shanghai Materials Genome Institute Shanghai University

In the present work,stress relaxation tests,high-resolution transmission electron microscopy（HRTEM） and molecular dynamics（MD） simulations were conducted on coarse-grained（cg）,nanograined（ng） and nanotwinned（nt） copper at temperatures ranging from room temperature to 75 ℃.The comprehensive investigations provide sufficient information for the building-up of a formula to describe the time,stress and temperature-dependent deformation and clarify the relationship among the strain rate sensitivity parameter,stress exponent and activation *** experimental and simulation results also suggest that under high stress level,dislocation-mediated plastic deformation is predominant in all cg,ng and nt *** low stress level,the grain boundary（GB） diffusion-associated deformation is dominant in the ng and cg specimens,whereas twin boundary（TB） migration,i.e.,twinning and detwinning with parallel partial dislocations,governs the time,stress and temperature-dependent deformation in the nt specimens.

关键词： Stress Relaxation nanotwin Copper HRTEM Atomistic Simulations

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