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Mechanical anisotropy and electronic properties of X2N2(XH2):first-principles calculations

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Communications in Theoretical Physics 2020年第11期72卷 109-120页

作者：李小珍邢孟江 Department of Information and Technology Kunming UniversityKunming650214China State Key Laboratory of Electronic Thin Films and Integrated Devices University of Electronic Science and Technology of ChinaChengdu610054China

The Mechanical anisotropy,structural properties,electronic band structures and thermal properties of C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)are detailed and investigated in this work.The novel silicon nitride phase Si2N2(SiH2)and germanium nitride phase Ge2N2(GeH2)in the Cmc21 structure are proposed in this work.The novel proposed Si2N2(SiH2)and Ge2N2(GeH2)are both mechanically and dynamically stable.The electronic band calculation of the HSE06 hybrid functional shows that C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)are all wide band gap semiconductor materials,and C2N2(CH2)and Si2N2(SiH2)are direct band gap semiconductor materials,while Ge2N2(GeH2)is a quasi-direct band gap semiconductor material,the band gap of C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)are 5.634 eV,3.013 eV,and2.377 eV,respectively.The three-dimensional and plane distributions of Young’s modulus,shear modulus and Poisson’s ratio of C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)show that these materials have different degrees of Mechanical anisotropy.The order of Young’s modulus of Si2N2(SiH2)and Ge2N2(GeH2)in different directions is different from that of C2N2(CH2).When the tensile axis is in a particular direction,the order of the Young’s modulus of Si2N2(SiH2):E[110]

关键词： X2N2(XH2) Mechanical anisotropy wide band gap semiconductor Young’s modulus

Effects of icosahedral phase on Mechanical anisotropy of as-extruded Mg-14Li (in wt%) based alloys

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Journal of Materials Science & Technology 2019年第11期35卷 2477-2484页

作者： Chuanqiang Li Daokui Xu Baojie Wang Liyuan Sheng Ruizhi Wu Enhou Han Peking University Shenzhen InstituteShenzhen Key Lab Human Tissue Regenerate&RepairShenzhen 518057China Key Laboratory of Nuclear Materials and Safety Assessment Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Materials and Energy Guangdong University of TechnologyGuangzhou 510006China School of Environmental and Chemical Engineering Shenyang Ligong UniversityShenyang 110159China Key Laboratory of Superlight Materials&Surface Technology Ministry of EducationHarbin Engineering UniversityHarbin 150001China

Through investigating and comparing microstructure and crystallographic texture of as-extruded Mg-14Li and Mg-14Li-6Zn-1Y(in wt%)alloys,the differences in their Mechanical anisotropy were investigated.It revealed that the formation of I-phase(Mg3Zn6Y,icosahedral structure)can effectively refine grain size.Moreover,compared with Mg-14Li alloy,the texture type of Mg-14Li-6Zn-1Y alloy changed slightly,but its texture intensity decreased remarkably.As a result,the stronger texture contributed to the"normal"Mechanical anisotropy of Mg-14Li alloy with higher tensile strength and a lower elongation ratio along transverse direction(TD)than those along extrusion direction(ED).However,for Mg-14Li-6Zn-1Y alloy,the zonal distribution of I-phase particles along ED caused"abnormal"Mechanical anisotropy,i.***.higher tensile strength and better plasticity along ED.

关键词： Mg-Li alloys Texture I-phase Mechanical anisotropy Fracture

Meso-Mechanical anisotropy and fracture evolution of reef limestones from the Maldives Islands and the South China Sea

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第12期15卷 3173-3187页

作者： Lihui Li Chenglong Li Beixiu Huang Jianguang Li Shouding Li Xiao Li Key Laboratory of Shale Gas and Geoengineering Institute of Geology and GeophysicsChinese Academy of SciencesBeijing100029China Innovation Academy for Earth Science Chinese Academy of SciencesBeijing100029China College of Earth and Planetary Sciences University of Chinese Academy of SciencesBeijing100049China College of Geoscience and Surveying Engineering China University of Mining and TechnologyBeijing100083China AVIC Institute of Geotechnical Engineering Co. Ltd.Beijing100098China

Reef limestone is a biogenic sedimentary rock widely distributed in coral reef areas, acting as an important foundation for coast construction. Due to its special biogenic origin, reef limestone is different from conventional rocks both in terms of rock structure and mechanical properties. In this study, mesoscale uniaxial compression experiments with five different loading directions were conducted on two kinds of reef limestones from the Maldives Islands and the South China Sea, respectively. The real-time high-resolution videos and images of failure processes were recorded simultaneously to investigate the fracture evolution and fracture surface roughness of reef limestones. It demonstrated that the reef limestones belonged to extremely soft to soft rocks, and their uniaxial compressive strength (UCS) values fluctuated with high discreteness. The mesoscale mechanical properties of reef limestones were highly anisotropic and mainly controlled by pore structure. The occurrence of dissolution pores in reef limestone tended to intensify Mechanical anisotropy. With the integration of the fracture initiation and propagation features of reef limestones, it is supposed that the intrinsic mechanism of anisotropy was probably attributed to the differences in coral growth direction and dissolution. Furthermore, the quantified fracture surface roughness was revealed to have a good consistency with density and UCS for the reef limestones from the South China Sea. The findings are helpful for providing theoretical and experimental references for engineering construction in coral reef areas.

关键词： Reef limestone Mechanical anisotropy Failure mode Pore structure Fracture surface roughness

Ameliorating mechanical properties and reducing anisotropy of as-extruded Mg-1.0Sn-0.5Ca alloy via Al addition

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Progress in Natural Science:Materials International 2021年第5期31卷 722-730页

作者： Yanfu Chai Lei Shan Bin Jiang Huabao Yang Chao He Wenxing Hao Junjie He Qingshan Yang Ming Yuan Fusheng Pan School of mechanical and Electrical Engineering Shaoxing University State Key Laboratory of mechanical Transmissions College of Materials Science and Engineering Chongqing University College of Materials Science and Engineering Yunnan University School of Metallurgy and Material Engineering Chongqing University of Science and Technology

Effects of Al addition to a Mg–Sn–Ca ternary alloy on its microstructure and tensile properties after extrusion were studied via extrusion of Mg-1.0 Sn-0.5 Ca-x Al(x = 0, 0.8, 2.4 wt%) sheets and analysis of the extruded materials.The results showed that Al addition not only refined the grain size(from 9.8 ± 0.7 μm to 8.3 ± 0.4 μm and7.6 ± 0.5 μm) but also accelerated the generation of more second phase(from 0.98 to 1.72 and 4.32%). Except for the CaMgSn and Mg2Ca in Mg-1.0Sn-0.5 Ca alloy, new phase(Mg, Al)2Ca appeared after Al addition. The addition of Al into Mg–Sn–Ca alloy induced the textural variation from an initially ED-split double-peaked texture to a weakened texture, i.e., divergent elliptical texture, due to the effect of particle stimulated nucleation. This eventually contributed to the improvement of Mechanical anisotropy as well as the higher Hc value and n-value.For the strain hardening behavior when tension along the TD, the prolonged stage II of Al-modified alloys was closely connected with the additional TD textural components, accelerating the activation of more basal slip. The decreased θIII0 in stage III of Al-modified alloys is beneficial to the grain refinement and the emergence of more second phase.

关键词： Mg–Sn–Ca alloy Al content Microstructure Texture Mechanical anisotropy

anisotropy of wrought magnesium alloys: A focused overview

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Journal of Magnesium and Alloys 2022年第6期10卷 1476-1510页

作者： Baodong Shi Chong Yang Yan Peng Fucheng Zhang Fusheng Pan National Engineering Research Center for Equipment and Technology of Cold Rolled Strip School of Mechanical EngineeringYanshan UniversityHebei-West-Str.438Qinhuangdao 066004PR China State Key Laboratory of Metastable Materials Science and Technology Yanshan UniversityQinhuangdao 066004PR China National Engineering Research Center for Magnesium Alloys(CCMg) Chongqing UniversityChongqing 400044PR China

In this paper, the relationship between anisotropic mechanical properties and the corresponding microstructure evolution of wrought magnesium alloys is critically reviewed. Experimental observations of the strong anisotropy(including the strength differential effect) induced by texture and twinning are discussed under different loading conditions(i.e., monotonic, cyclic and multiaxial loading). An accurate constitutive model is essential to describe the mechanical responses and to predict the forming performance considering engineering applications. Therefore, macroscale constitutive modeling of the anisotropy of magnesium alloys with directional distortional hardening are comprehensively reviewed with different approaches. To clarify the origin of the anisotropic behavior, physics-based mesoscale modeling of the anisotropy is also compared in detail.

关键词： Wrought Mg alloys Mechanical anisotropy Deformation mechanism Constitutive modeling

Quantitative study on the tension-compression yield asymmetry of a Mg-3Al-1Zn alloy with bimodal texture components

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Journal of Magnesium and Alloys 2022年第6期10卷 1680-1693页

作者： Lingyu Zhao Wenhao Chen Beian Zhou Cong He Changjian Yan Zhaoyang Jin Huihui Yu Yunchang Xin School of mechanical Engineering Yangzhou UniversityYangzhou 225127China Key Laboratory for Light-weight Materials Nanjing Tech University 10009China National Institute for Materials Science 1-2-1 SengenTsukub1305-0047Japan Institute of Corrosion Science and Technology Guangdong 510070China Institute of Applied Physics Jiangxi Academy of SciencesNanchang 330029China

This study demonstrates the yield asymmetry in Mg-3Al-1Zn alloy containing both ND-texture(c-axis//ND(Normal direction))and TD-texture(c-axis//TD(Transverse direction))in a quantitative view.The results showed that the yield asymmetry is strongly dependent on the distribution of bimodal texture components,on the basis of the successful establishment of the quantified relationship between pre-deformation parameters and texture components distribution.It’s meaningful for providing key reference to texture design.mechanical behavior of bimodal textured Mg alloy under tension and compression was tested.CYS/TYS(compressive yield stress/tensile yield stress)equal to 1 is obtained,implying that the yield asymmetry is eliminated when two textures distribute at specific fractions.The corresponding mechanism for the texture-dependence of tension-compression yield asymmetry is revealed by the analysis of slip/twinning activities and a compound use of the activation stress difference of slip/twinning(ΔStress)and geometrical compatibility factor(m′)between neighboring grains.Balanced activity of{10■2}twinning and a quite similar boundary obstacle effect against slip/twinning transfer under tension and compression accounts for such good symmetry performance.

关键词： Mg alloy Texture Mechanical anisotropy Twinning Slip

mechanical and Corrosion Behavior of a Biomedical Mg–6Zn–0.5Zr Alloy Containing a Large Number of Twins

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Acta Metallurgica Sinica(English Letters) 2023年第3期36卷 439-455页

作者： Chang‑Jian Yan Bo Guan Yun‑Chang Xin Ling‑Yu Zhao Guang‑Jie Huang Rui Hong Xiao‑Bo Chen Paul K.Chu Institute of Corrosion Science and Technology Guangdong 510070China International Joint Laboratory for Light Alloys College of Materials Science and EngineeringChongqing UniversityChongqing 400030China Key Laboratory for Light‑Weight Materials Nanjing Tech UniversityNanjing 210009China School of mechanical Engineering Yangzhou UniversityYangzhou 225127China School of Engineering RMIT UniversityCarlton 3053VICAustralia Department of Physics Department of Materials Science&EngineeringDepartment of Biomedical EngineeringCity University of Hong KongTat Chee AvenueKowloonHong KongChina Institute of Metal Research Chinese Academy of SciencesShenyang 110016China

The strong texture of Mg alloys can lead to strong tension–compression yield asymmetry and corrosion anisotropy,and this will consequently affect the effectiveness of hard tissue implants.A biomedical Mg–6Zn–0.5Zr alloy containing a large number of{1012}primary twins and{1012}–{1012}secondary twins is successfully prepared by cross compression.The dual twin structure not only removes the tension–compression yield asymmetry completely,but effectively reduces the corrosion anisotropy without compromise of corrosion resistance.The difference between the largest corrosion rate and smallest one is~1.2 times compared to~1.6 times of the original materials.It is found that the reduced corrosion anisotropy is related to re-distribution of crystallographic orientations by twins.

关键词： Biomedical Mg alloy Corrosion Mechanical anisotropy Texture Twins

Effect of crushing methods on morphology and magnetic properties of anisotropic NdFeB powders

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Journal of Rare Earths 2017年第8期35卷 800-804页

作者：王仁全刘颖李军储林华杨晓娇邱彧冲 College of Materials Science and Engineering Sichuan University Chengdu 610065 China

Crushing is a critical factor for the anisotropic Nd Fe B powders with high magnetic properties. However, the traditional crushing methods of disk-milling（DM） or impact crushing（IC）, are difficult to obtain high-performance powders. Herein, a new method of preparing anisotropic powders with high performance was reported, which was through crushing the hot-deformed magnets perpendicular to c-axis direction（shear crushing, SC）. The microstructure and alignment of the magnets were examined by scanning electron microscopy（SEM） and X-ray diffraction（XRD）, respectively. The results indicated that the cracks mainly extended along the Nd-rich grain boundary phase and/or the binding interface of ribbons. It not only could protect the magnetic phase from being damaged, but also could keep the grains integrated. Therefore, shear crushing was an effective method for the preparation of highperformance anisotropic powders and then to fabricate the bonded magnets with Br=9.0 kGs, Hci=10.48 kOe and（BH）max=17.7 MGOe.

关键词： hot-deformation Mechanical anisotropy crushing microstructure rare earths

On the texture evolution of Mg-Zn-Ca alloy with different hot rolling paths

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Journal of Magnesium and Alloys 2017年第2期5卷 166-172页

作者： Q.Li G.J.Huang X.D.Huang S.W.Pan C.L.Tan Q.Liu College of Materials Science and Engineering Chongqing UniversityChongqing 400044China State Key Laboratory for Advanced Metals and Materials University of Science and Technology BeijingBeijing 100083China

In the present study,the texture evolution and Mechanical anisotropy in a typical Mg–Zn–Ca alloy through hot cross rolling(CR)and unidirectional rolling(UR)were systematically studied.The results show that the rolling path greatly affects the annealed texture.The UR develops a texture with basal poles mainly distributing along the transverse direction(TD).By contrast,an ellipse-like(0002)texture with basal pole inclining largely away from the normal direction(ND)is developed after hot cross rolling and annealing.Therefore,the CR is an effective method to tailor the texture of the experimental alloy.Unfortunately,this ellipse-like texture could not reserve during the subsequent unidirectional hot rolling and annealing.Both UR and CR plates exhibit a strong planar Mechanical anisotropy compared with the traditional unidirectional rolled plate.

关键词： Mg alloys Hot cross rolling Texture Mechanical anisotropy