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grain-refining and strengthening mechanisms of bulk ultrafine grained CP-Ti processed by L-ECAP and MDF

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Journal of Materials Science & Technology 2021年第24期83卷 196-207页

作者： Peng-Cheng Zhao Guang-Jian Yuan Run-Zi Wang Bo Guan Yun-Fei Jia Xian-Cheng Zhang Shan-Tung Tu Key Laboratory of Pressure Systems and Safety Ministry of EducationSchool of Mechanical and Power EngineeringEast China University of Science and TechnologyShanghai200237China National Engineering Research Center for Magnesium Alloys Chongqing UniversityChongqing400044China

The microstructural evolution and mechanical properties of ultrafine-grained(UFG)CP-Ti after an innovative large-volume equal channel angular pressing(L-ECAP)and multi-directional forging(MDF)were systematically examined using monotonic tensile tests combined with transmission electron microscope(TEM)and electron backscatter diffraction(EBSD)*** refined and homogeneous microstructures were achieved after L-ECAP(8-pass and 12-pass)and MDF(2-cycle and 3-cycle),respectively,where the grain size distribution conformed to lognormal *** grain refinement of450℃L-ECAP is dominated by dynamic recrystallization(DRX)and dynamic recovery(DRV),while that of MDF is dominated by *** iron impurities promote recrystallization by pinning-induced dislocation accumulation so that DRX is prone to occur at iron segregation regions during *** monotonic tensile results show that the strain hardening rate of CP-Ti increases with the decrease of grain size,while the continuous strain hardening ability *** relationship between the average grain size and yield strength is in accordance with Hall-Petch ***,the individual strengthening mechanisms were quantitatively examined by the modified *** results indicate that the strengthening contribution of dislocation accumulation to yield strength is greater than that of grain refinement.

关键词： Equal channel angular pressing Multi-directional forging ultrafine grain Recrystallization Strain hardening Hall-Petch relation

Effect of Pre-deformation on grain Ultrafining by Intercritical Deformation in Low-Carbon Microalloyed Steels

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Acta Metallurgica Sinica(English Letters) 2018年第10期31卷 1038-1048页

作者： Ba Li Qing-You Liu Shu-Jun Jia Yi Ren Bing Wang Central Iron and Steel Research Institute Beijing 100081China Iron and Steel Research Institute Ansteel Group Co. Ltd.Anshan 114009 China

In this study, the effect of pre-deformation at recrystallization and non-recrystallization zone on the grain ultrafining by the subsequent intercritical deformation （ID） was investigated on low-carbon microalloyed steel. The results showed that ultrafine grain microstructure with an average size of - 1.0 μm was fabricated through pre-deformation in the recrys- tallization zone followed by ID. When pre-deformed at the non-recrystallization zone prior to ID, the grain size increased to 1.6 μm with a heterogeneous distribution along with the well-developed dynamic recovery of ferrite. The grain ultrafining mechanism was attributed to the combined action of the deformation-induced ferrite transformation and the continuous dynamic recrystallization. In particular, the continuous dynamic recrystallization process during ID occurred on the pro-eutectoid ferrite as a result of the subgrain rotation mechanism and the absorbing dislocations mechanism.

关键词： Low-carbon microalloyed steels Intercritical deformation ultrafine grain Continuous dynamic recrystallization Deformation-induced ferrite transformation

In situ neutron diffraction revealing the achievement of excellent combination of strength and ductility in metastable austenitic steel by grain refinement

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Journal of Materials Science & Technology 2024年第9期176卷 69-82页

作者： Wenqi Mao Wu Gong Stefanus Harjo Satoshi Morooka Si Gao Takuro Kawasaki Nobuhiro Tsuji J-PARC Center Japan Atomic Energy AgencyIbarakiJapan Department of Materials Science and Engineering Kyoto UniversitySakyo-kuKyotoJapan

The yield stress of Fe-24Ni-0.3C(wt%)metastable austenitic steel increased 3.5 times(158→551 MPa)when the average grain size decreased from 35μm(coarse-grained[CG])to 0.5μm(ultrafine-grained[UFG]),whereas the tensile elongation was kept large(0.87→0.82).In situ neutron diffraction measurements of the CG and UFG Fe-24Ni-0.3C steels were performed during tensile deformation at room temperature to quantitatively elucidate the influence of grain size on the mechanical properties and deformation *** initial stages of plastic deformation in the CG and UFG specimens were dominated by dislocation slip,with deformation-induced martensitic transformation(DIMT)also occurring in the later stage of *** show that grain refinement increases the initiation stress of DIMT largely and suppresses the rate of DIMT concerning the strain,which is attributed to the following effects.(i)grain refinement increased the stabilization of austenite and considerably delayed the initiation of DIMT in the//LD(LD:loading direction)austenite grains,which were the most stable grains for *** a result,most of the//LD austenite grains in the UFG specimen failed to transform into martensite.(ii)grain refinement also suppressed the autocatalytic effect of the martensitic ***,the DIMT with the low transformation rate in the UFG specimen was more efficient in increasing the flow stress and more appropriate to maintain uniform deformation than that in the CG specimen during *** above phenomena mutually contributed to the excellent combination of strength and ductility of the UFG metastable austenitic steel.

关键词： ultrafine grain Deformation-induced martensitic transformation Metastable austenitic steel In situ neutron diffraction

New Heat Treatment Technology for grain Refining of Structural Steel

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Journal of Iron and Steel Research International 2005年第6期12卷 49-53页

作者： Lü Bo ZHANG Fu-cheng CAO Guo-hua ZHANG Ji-ming Yanshan University Qinhuangdao 066004 China Key Laboratory of Metastable MaterialsScience and Technology Qinhuangdao 066004 China）

The application of electrical contact heating （ECH） in austenitic grain refining of ultra-pure 42CrMoVNb steel was introduced. The ECH equipment was designed to reach uniform heating of uniform heat transfer in the sample. The 42CrMoVNb steel treated possesses uniform microstructure with an average austenite grain size of 1.4 μm, higher strength （1 538 MPa） and impact toughness （81J/cm^2）.

关键词： electrical contact heating medium carbon alloy steel ultrafine grain 42CrMoVNb

Temperature-dependent tensile properties of ultrafine-grained C-doped CoCrFeMnNi high-entropy alloy

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Rare Metals 2022年第8期41卷 2877-2885页

作者： Yan-Zhong Tian Si-Yuan Peng Shang-Feng Chen Zi-Jian Gu Yang Yang Xiu-Ling Shang Guan-Yu Deng Li-Hong Su Shi-Jie Sun Key Laboratory for Anisotropy and Texture of Materials(Ministry of Education) School of Materials Science and EngineeringNortheastern UniversityShenyang110819China Innovation Center of GD Midea Air-Conditioning Equipment Co. LtdFoshan528311China School of Mechanical MaterialsMechatronic and Biomedical EngineeringUniversity of WollongongWollongongNSW2500Australia Institute of Metal Research Chinese Academy of SciencesShenyang110016China

Metallic materials can be strengthened by various kinds of plastic deformation ***,the deformed materials suffer poor ductility and thermal stability due to the high-density *** this work,we prepared fully recrystallized ultrafine-grained(UFG)1%CCoCrFeMnNi high-entropy alloy(C-HEA)through cold rolling and annealing ***-static tensile tests were performed at temperatures between 77 and 823 *** micros true tures of the samples after tensile tests were characterized,and deformation mechanisms were *** is a transition of deformation mechanisms from twinning and dislocation slip to dislocation slip and grain boundary sliding with temperature *** UFG C-HEA exhibits balanced strength and ductility from the cryogenic temperature to high temperatures,indicating highly adaptive microstructure and mechanical *** strength and uniform elongation of the UFG C-HEA decrease monotonously with temperature increasing,but the elongation to failure exhibits the lowest value at the medium *** grain boundary sliding is supposed to assist the unconventionally high elongation at 823 K.

关键词： High-entropy alloy Temperature Ductility Strength ultrafine grain

ultrafine-grained Ti6Al7Nb-xCu alloy with ultrahigh strength and exceptional biomedical properties

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Journal of Materials Science & Technology 2023年第33期164卷 68-78页

作者： Yi Li Hai Wang Konrad Koenigsmann Hui Liu Shuyuan Zhang Ling Ren Ke Yang Shi-changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China University of Chicago ChicagoIL 60637USA Binzhou Institute of Technology Shandong Key Laboratory of Advanced Aluminum Materials and TechnologyBinzhou 256606China

grain refinement has been found to be able to improve the strength of metals without reducing their plasticity or *** this work,ultrafine-grained Ti6Al7Nb-xCu(x=0,3 wt%,6 wt%,9 wt%)alloys were fabricated based on the clinically used Ti6Al7Nb alloy via Cu alloying fabrication strategy combined with dynamic recrystallization(DRX)from martensite during hot *** results indicate that Cu alloying is not only effective in reducing the width of martensite laths after quenching in theβphase region but also increases the nucleation rate of DRX during the high-temperature ***,the Ti2Cu phase that precipitates from the matrix can pin the grain boundaries and inhibit their growth during the high-temperature *** optimal Cu concentration of Ti6Al7Nb-xCu alloy is determined to be 6 wt%,and the optimal deformation temperature is determined to be 750°*** this Cu content and deformation temperature,the grain size is only 270 nm,the tensile strength is up to 1266±10 MPa,and the elongation is 17%.Compared with the commercial Ti6Al7Nb alloy,the ultrafine-grained Ti6Al7Nb-6Cu alloy has better overall mechanical properties,good biocompatibility,and unique antibacterial *** work provides a theoretical basis for fabricating the new antibacterial titanium-based alloys with high strength.

关键词： High strength titanium alloy ultrafine grain Antibacterial Dynamic recrystallization

Preparation of an ultrafine-grained Fe-40Al intermetallic compound

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Acta Metallurgica Sinica(English Letters) 2010年第1期23卷 50-56页

作者： Jiqiang MA Jun YANG Qinling BI Weimin LIU State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of Sciences Lanzhou 730000 China Graduate University of Chinese Academy of Sciences Beijing 100039 China

An ultrafine grained Fe-40Al intermetallic compound is fabricated by a self- propagating high temperature synthesis （SHS） casting. The XRD result shows that the Fe-40Al intermetallic compound consists of the B2 FeAl phase. The Fe-40Al intermetallic compound presents ultrafine grain size in the range of 100-600 rim, leading from the high nucleation rate and the low growth rate. The Fe-40Al intermetallic compound exhibits high hardness （3.4 GPa） and high bending strength （830 MPa） and high compressive strength （2700 MPa）, which originate from the ultrafine-structure in the material. The effect of the load on dry-sliding wear rate of the material against AISI52100 steel was investigated. The wear rate increases with the increase of normal load. The dominated weax mechanism is microfracture.

关键词： Iron aluminides Self-propagating high temperature synthesis (SHS) casting ultrafine grain Preparation Wear

ultrafine-grained Microstructure and Improved Mechanical Behaviors of Friction Stir Welded Cu and Cu–30Zn Joints

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Acta Metallurgica Sinica(English Letters) 2018年第8期31卷 878-886页

作者： Yan-Fei Wang Jian An Kun Yin Ming-Sai Wang Yu-Sheng Li Chong-Xiang Huang School of Aeronautics and Astronautics Sichuan University Nano Structural Materials Center School of Materials Science and Engineering Nanjing University of Science and Technology

Ultra-strong joints of pure Cu and Cu–30Zn alloy were obtained by friction stir welding under flowing water. The effects of heat inputting condition and material characteristics on the morphologies, microstructures and mechanical properties of welding joints were studied. Defect-free stirring zones of pure Cu and Cu–30Zn were characterized by onion-ringed structure and plastic flowing bands, respectively. Both low stacking fault energy and fast cooling condition contributed to the formation of small recrystallized grains less than 1 μm in stirring zones. The welding joints in both materials exhibited enhanced mechanical performances due to ultrafine-grained microstructure in stirring zones and disappearance of soft heataffected-zone. The technique of digital image correlation was used to study the tensile deformation behaviors of welding joints and verify the improved tensile properties.

关键词： Friction stir welding ultrafine grain Mechanical properties Stacking fault energy Digital image correlation(DIC)

Superplastic behavior of an ultrafine-grained Mg-13Zn-1.55Y alloy with a high volume fraction of icosahedral phases prepared by high-ratio differential speed rolling

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Journal of Materials Science & Technology 2017年第9期33卷 919-925页

作者： T.Y.Kwak W.J.Kim Rare Metal R&BD Group Korea Institute of Industrial Technology Department of Materials Science and Engineering Hongik University

An ultrafine-grained（UFG） Mg-13Zn-1.55 Y alloy（ZW132） with a high volume fraction（7.4%） of icosahedral phase（I-phase, Mg;Zn;Y） particles was prepared by applying high-ratio differential speed rolling（HRDSR） on the cast microstructure following homogenization. The alloy exhibited excellent superplasticity at low temperatures(tensile elongations of 455% and 1021% 473 K-10;s;and 523 K-10;s;,respectively). Compared with UFG Mg-9.25Zn-1.66 Y alloy（ZW92） with a lower volume fraction of I-phase particles（4.1%）, which was prepared using the same processing routes, the UFG ZW132 alloy exhibited a higher thermal stability of grain size. Rapid grain coarsening, however, occurred at temperatures beyond523 K, leading to a loss of superplasticity. The high-temperature deformation behavior of the HRDSRprocessed ZW132 alloy could be well described assuming that the mechanisms of grain boundary sliding and dislocation climb creep competed with each other and considering that the grain-size was largely increased by accelerated grain growth at the temperatures beyond 523 K.

关键词： Magnesium alloy Superplastic deformation ultrafine grain Icosahedral quasicrystal grain growth