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High-temperature fatigue strength of grain boundaries with different misorientations in nickel-based superalloy bicrystals

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Journal of Materials Science & Technology 2023年第23期154卷 94-106页

作者： D.F.Shi z.J.zhang Y.H.Yang Y.z.zhou R.Liu P.zhang z.F.zhang Shi-changxu Innovation Center for Advanced Materials Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China School of Materials Science and Engineering University of Science and Technology of China Shenyang 110016 China

Nickel-based single-crystal superalloys are widely used in the manufacture of aeroengine turbine vanes for their excellent high-temperature performance. Low-angle grain boundaries (LAgBs) will be generated inevitably during their manufacture, which are often characterized by grain boundary misorientation (gBM) and will weaken the mechanical properties of superalloys. However, the relationship between gBM and the fatigue properties of superalloys at elevated temperatures has seldom been investigated due to the difficulty in the sample preparation and experiment process. Based on six kinds of bicrystals with different tilt LAgBs made by a second-generation single-crystal superalloy, the effects of misorientation on the grain boundary microstructure and fatigue properties (980 °C) of superalloys were studied systematically in this work. It is found that, with the increase of gBM, the gB precipitates combined with the cast micropores increase monotonically, accordingly both the fatigue life and fatigue strength decrease successively. Fatigue fracture observations show that the cracks of all the bicrystals initiated from the cast micropores at gBs, and then propagated along the gBs. Therefore, the coupling effect of cast micropores and gBM on the fatigue damage mechanisms of the bicrystals are evaluated according to their hindering degrees on the piled-up dislocations. Combining with a hysteresis energy model, a quantitative fatigue strength prediction model of superalloys is established and is well verified by abundant experimental data. This study could provide guidance for fatigue performance prediction and structural design of superalloys.

关键词： Superalloys Bicrystals grain boundary misorientation Fatigue strength Fatigue crack

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Strain-induced formation of a gradient nanostructured surface layer on an ultrahigh strength bearing steel

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Journal of Materials Science & Technology 2018年第9期34卷 1676-1684页

作者： K.zhang z.B.Wang Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of SciencesShenyang 110016 China University of Chinese Academy of Sciences Beijing 100049 China

In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twins and cementite particles in the initial microstructure underwent distinct plastic strains and were gradually refined into nanostructures. Consequently, a gradient nanostructured（gNS） surface layer with a mean grain size of -24 nm at the top surface was obtained on the bearing steel, resulting in an increment of -20% in the surface hardness. Analyses based on microstructural evolution, phase constitution and in-depth hardness distribution revealed a mechanically induced formation mechanism of the gNS surface layer. The multiple surface severe plastic deformation under fine lubrication and cooling during SMRT contributed to the formation of a thick hardened surface layer on the bearing steel.

关键词： gradient nanostructured Ultrahigh strength bearing steel Plastic deformation Martensite Surface mechanical rolling treatment

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Oxygen transfer in human carotid artery bifurcation

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Acta Mechanica Sinica 2007年第3期23卷 305-309页

作者： z. g. zhang Y. B. Fan X. Y. Deng Dalian University of Technology Dalian 116023 China Department of Bioengineering Beihang UniversityBeijing 100083 China

Arterial bifurcations are places where blood flow may be disturbed and slow recirculation flow may occur. To reveal the correlation between local oxygen transfer and atherogenesis, a finite element method was employed to simulate the blood flow and the oxygen transfer in the human carotid artery bifurcation. Under steady-state flow conditions, the numerical simulation demonstrated a variation in local oxygen transfer at the bifurcation, showing that the convective condition in the disturbed flow region may produce uneven local oxygen transfer at the blood/wall interface. The disturbed blood flow with formation of slow eddies in the carotid sinus resulted in a depression in oxygen supply to the arterial wall at the entry of the sinus, which in turn may lead to an atherogenic response of the arterial wall, and contribute to the development of atherosclerotic stenosis there.

关键词： Atherosclerosis Carotid artery Secondary flow Mass transfer

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Shear band evolution and mechanical behavior of cold-rolled zr-based amorphous alloy sheets:An in-situ study

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Journal of Materials Science & Technology 2024年第14期181卷 115-127页

作者： C.Y.zhang z.W.zhu S.T.Li Y.Y.Wang z.K.Li H.Li g.Yuan H.F.zhang School of Metallurgy Northeastern UniversityShenyang 110819China Shi-changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China The State Key Laboratory of Rolling and Automation(RAL) Northeastern UniversityShenyang 110819China

Cold rolling process can regulate the microstructure and mechanical properties of amorphous alloys,but it is still a challenging task to reveal their microscopic ***,we designed an in-situ SEM observation device for the cold rolling process of amorphous alloy,and visually observed the formation and evolution of shear bands during single-pass and multi-pass rolling process of the zr_(55)Cu_(30)Al_(10)Ni_(5)amorphous alloy *** is found that the evolution process of shear bands in the rolling process of amorphous alloy shows heritability,which is mainly reflected in two aspects:one is that the shear band formation pattern in the single-pass rolling process is more inclined to inherit the previous shear band formation pattern;the other is that the shear deformation is more likely to occur in the pre-existing shear bands in the multi-pass rolling *** rule can be used to guide the controlled genera-tion of shear bands in amorphous ***,we emphasized the importance of pre-existing shear band orientations and systematically investigated the mechanical behavior of the amorphous alloys with pre-existing shear bands by in-situ SEM *** is found that the mechanical properties of the as-rolled amorphous alloys are determined by the competition between the work-softening of the pre-existing shear band itself and the work-hardening caused by the blocking effect of the pre-existing shear bands on the shear *** on this,we enhance the tensile fracture strength and the tensile ductility of the amorphous alloy by adjusting the orientation of the pre-existing shear bands parallel to the tensile stress axis so that the pre-existing shear bands prevent the linear propagation and destruction of the new shear bands.

关键词： Amorphous alloy Cold rolling Shear band Mechanical behavior In-situ study Plasticity

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Pseudospin-1 Physics of Photonic Crystals

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Research 2019年第1期2019卷 1062-1076页

作者： A.Fang z.Q.zhang Steven g.Louie C.T.Chan Department of Physics Te Hong Kong University of Science and TechnologyClear Water BayHong KongChina Institute for Advanced Study Te Hong Kong University of Science and TechnologyClear Water BayHong KongChina Department of Physics University of California at BerkeleyBerkeleyCA 94720USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA

We review some recent progress in the exploration of pseudospin-1 physics using dielectric photonic crystals(PCs).We show some physical implications of the PCs exhibiting an accidental degeneracy induced conical dispersion at theΓpoint,such as the realization of zero refractive index medium and the zero Berry phase of a loop around the nodal *** photonic states of such PCs near the Dirac-like point can be described by an efective spin-orbit Hamiltonian of *** wave propagation in the positive,negative,and zero index media can be unifed within a framework of pseudospin-1 description.A scale change in PCs results in a rigid band shif of the Dirac-like cone,allowing for the manipulation of waves in pseudospin-1 systems in much the same way as applying a gate voltage in pseudospin-1/2 *** transport of waves in pseudospin-1 systems exhibits many interesting phenomena,including super Klein tunneling,robust supercollimation,and unconventional Anderson *** transport properties of pseudospin-1 systems are distinct from their counterparts in pseudospin-1/2 systems,which will also be presented for comparison.

关键词： realization applying Berry

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Effect of scanning strategy on grain structure and crystallographic texture of Inconel 718 processed by selective laser melting

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Journal of Materials Science & Technology 2018年第10期34卷 1799-1804页

作者： H.Y. Wan z.J. zhou C.P. Li g.F. Chen g.P. zhang Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China School of Materials Science and Engineering University of Science and Technology of China Shenyang 110016 China Materials & Manufacturing Qualification group Corporate Technology Siemens Ltd. Beijing 100102 China

Two types of scanning strategies were adopted to study the effect of scanning strategy on grain structure and crystallographic texture of selective laser melted （SLM） Inconel 718. The results show that bidirec-tional scanning without and with a 90°-rotation for every layer produced the bimodal grain structure and the directional columnar grain structure, respectively. Controlling the heat flux direction between the successive layers via scanning strategy enabled the formation of such different grain structures. Fur-thermore, when the 90°-rotation was applied, the competitive grain growth mechanism became more pronounced and the strong cube texture developed.

关键词： Selective laser melting Additive manufacturing Scanning strategy Texture grain structure

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High Temperature Oxidation and Wear Resistance of Y-modified Hot Dipping Aluminized Coating on SCH12 Steel

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稀有金属材料与工程 2012年第S1期41卷 231-235页

作者： Fan, X. S. Yang, z. g. zhang, C. Tsinghua Univ Dept Mat Sci & Engn State Key Lab New Ceram & Fine Proc Beijing 100084 Peoples R China

Microstructures,high-temperature oxidation and wear resistance of hot dipping Al-Si-Y coating on SCH12 heat resistant cast steel were investigated in this *** aluminized coating was characterized by scanning electron microscopy(SEM),energy dispersive X-ray spectrometry(EDX)and X-ray diffraction(XRD).The results showed that the coating was composed of the Al-rich outer layer and the intermetallics inner *** the Al-rich layer,some Y-rich precipitates and Fe-Al-Si-Cr precipitates could be *** intermetallics layer presented three layers induced by the increase of Fe,Cr,Ni content and the corresponding decrease of Al,Si *** oxidation tests were conducted in still air at 850℃for up to 100 *** oxidation,a top oxide scale composed of mainlyα-Al2O3,Al5Y3O12 was formed on the steel *** intermetallics beneath the oxide scale consisted of mainly FeAl and small amount of Fe2Al5 and Cr3Si *** mass gain of the coated and uncoated SCH1steel is 0.45 mg/cm 2 and 0.57 mg/cm 2,*** wear resistance was investigated using a high-temperature pin-on-disc tribometer at 650℃.The wear rate for the coated and uncoated steel is 0.45μm 3 /μm.N and 3.01μm 3 /μm.N,*** high temperature wear tests and oxidation tests results demonstrated that the yttrium-modified aluminized specimen had significantly improved high-temperature wear resistance and equivalent oxidation resistance compared with the original SCH12 specimen.

关键词： hot dipping aluminizing oxidation resistance high-temperature wear resistance

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Effect of stress profile on microstructure evolution of cold-drawn commercially pure aluminum wire analyzed by finite element simulation

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Journal of Materials Science & Technology 2018年第7期34卷 1214-1221页

作者： Y.K.zhu Q.Y.Chen Q.Wang H.Y.Yu R.Li J.P.Hou z.J.zhang g.P.zhang z.F.zhang Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences National Quality Supervision & Inspection Center of Electrical Equipment Safety Performance Zhejiang Huadian Equipment Testing Institute

The evolution of microstructure in the drawing process of commercially pure aluminum wire （CPAW） does not only depend on the nature of materials, but also on the stress profile. In this study, the effect of stress profile on the texture evolution of the CPAW was systematically investigated by combining the numerical simulation and the microstructure observation. The results show that the tensile stress at the wire center promotes the formation of 〈111〉 texture, whereas the shear stress nearby the rim makes little contribution to the texture formation. Therefore, the 〈111 〉 texture at the wire center is stronger than that in the surface layer, which also results in a higher microhardness at the center of the CPAW under axial loading.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

关键词： Commercially pure aluminum wire Cold drawing Texture Finite element simulation Stress profile

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Mechanical Alloying Effect on the Structure of Fe-Al-(Si) Alloy

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Journal of Materials Science & Technology 1997年第3期13卷 219-222页

作者： zhang, JQ Wu, BY Hu, z Wang, gQ SOUTHEAST UNIV DEPT MECH ENGNNANJING 210096PEOPLES R CHINA NANJINg UNIV DEPT CHEMNANJING 210008PEOPLES R CHINA NANJINg UNIV DEPT PHYSNANJING 210008PEOPLES R CHINA

The mechanical alloying effects on the structures of Fe71.3Al28.4(CeO2)(0.3) and Fe73.3Al9.8-Si-16.6(CeO2)(0.3) samples have been investigated mainly by Mossbauer spectroscopy and X-ray diffraction. it is found that with the increase of milling time, a substituting disordered alpha-Fe solution is formed gradually and almost completed after milled for 72 h. Further increasing milling time causes the atomic rearrangement within the powders. Correspondingly, the average lattice parameter and average crystalline size change until 72 h and remain constant after 72 h. The addition of Si leads to the higher disordered degree reflected in the smaller average hyperfine field and larger mean square deviation.

关键词： Iron alloys

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PRECIPITATION AND gROWTH OF PEROVSKITE PHASE IN TITANIUM BEARINg BLAST FURNACE SLAg

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Acta Metallurgica Sinica(English Letters) 2007年第1期20卷 9-14页

作者： z.z. guo T.P. Lou L. zhang L.N. zhang z.T. Sui School of Materials and Metallurgy Northeastern University Shenyang 110006 Ghina

The effects of transformation of slag composition and additive agents on the morphology, the precipitation behavior, the crystal growth, and the volume fraction (VF) of perovskite (CaO·¤TiO_2) crystal in the Ti-bearing blast furnace slags were investigated. As the morphology of perovskite is dispersed in molten slags, the crystal growth mechanism of the melting of fine dendrites and the coarsening of large grains exist throughout the solidification of molten slags. With the increase of CaO and Fe_2O_3 content, VF of perovskite obviously increases. However, high basicity leads to the viscosity of slag, which results in the reduction of the average equivalent diameter (AED). The experimental results showed that the presence of the additives CaF_2 and MnO efficiently decreased the viscosity of the slags, and obviously improved the morphology of perovskite and promoted its growth.

关键词： perovskite phase Ti-bearing blast furnace slag precipitation additive agent

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