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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)techniques.Substantially 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 distribution.The grain refinement of450℃L-ECAP is dominated by dynamic recrystallization(DRX)and dynamic recovery(DRV),while that of MDF is dominated by DRX.The iron impurities promote recrystallization by pinning-induced dislocation accumulation so that DRX is prone to occur at iron segregation regions during L-ECAP.The 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 decreases.The relationship between the average grain size and yield strength is in accordance with Hall-Petch relationship.Meanwhile,the individual strengthening mechanisms were quantitatively examined by the modified model.The 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

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 ductility.In 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 work.Our 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 deformation.Additionally,the Ti2Cu phase that precipitates from the matrix can pin the grain boundaries and inhibit their growth during the high-temperature deformation.The optimal Cu concentration of Ti6Al7Nb-xCu alloy is determined to be 6 wt%,and the optimal deformation temperature is determined to be 750°C.At 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 properties.This 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

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 strategies.However,the deformed materials suffer poor ductility and thermal stability due to the high-density defects.In this work,we prepared fully recrystallized ultrafine-grained(UFG)1%CCoCrFeMnNi high-entropy alloy(C-HEA)through cold rolling and annealing process.Quasi-static tensile tests were performed at temperatures between 77 and 823 K.Deformation micros true tures of the samples after tensile tests were characterized,and deformation mechanisms were discussed.There is a transition of deformation mechanisms from twinning and dislocation slip to dislocation slip and grain boundary sliding with temperature increasing.The UFG C-HEA exhibits balanced strength and ductility from the cryogenic temperature to high temperatures,indicating highly adaptive microstructure and mechanical properties.The 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 temperature.The 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

Role of extrusion rate on the microstructure and tensile properties evolution of ultrahigh-strength low-alloy Mg-1.0Al-1.0Ca-0.4Mn(wt.%)alloy

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Journal of Magnesium and Alloys 2023年第2期11卷 553-561页

作者： X.Q.Liu X.G.Qiao R.S.Pei Y.Q.Chi L.Yuan M.Y.Zheng School of Material Science and Engineering Harbin Institute of TechnologyHarbin 150001China Institut fur Metallkunde und Meterialphysik RWTH Aachen UniversityAachen D-52056Germany

Mg-1.0Al-1.0Ca-0.4Mn(AXM1104, wt.%) low alloy was extruded at 200 ℃ with an extrusion ratio of 25 and different ram speeds from 1.0 to 7.0 mm/s. The influence of extrusion rate on microstructure and mechanical properties of the AXM1104 alloy was systematically studied. With the increasing of extrusion rate, the mean dynamically recrystallized(DRXed) grain size of the low alloy and average particles diameter of precipitate second phases were increased, while the degree of grain boundary segregation and the intensity of the basal fiber texture were decreased. With the rising of extrusion rate from 1.0 to 7.0 mm/s, the tensile yield strength(TYS) of the as-extruded AXM1104 alloy was decreased from 445 MPa to 249 MPa, while the elongation to failure(EL) was increased from 5.0% to 17.6%. The TYS, ultimate tensile strength(UTS) and EL of the AXM1104 alloy extruded at the ram speed of 1.5 mm/s was 412 MPa, 419 MPa and 12.0%, respectively,exhibiting comprehensive tensile mechanical properties with ultra-high strength and excellent plasticity. The ultra-high TYS of 412 MPa was mainly due to the strengthening from ultra-fine DRXed grains with segregation of solute atoms at grain boundaries. The strain hardening rate is increase slightly with increasing extrusion speed, which may be ascribed to the increasing mean DRXed grain size with rising extrusion speed. The higher strain hardening rate contributes to the higher EL of these AXM1104 samples extruded at higher ram speed.

关键词： Mg-Al-Ca-Mn alloy ultrafine grain Extrusion rate grain boundary segregation Microstructure Ultrahigh strength

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

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

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）

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

Extrusion Upsetting Multiple Processing in Sandglass Die

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Rare Metals 2001年第1期20卷 62-65页

作者： Wenlin Lu, Yong Wang, Zezhou Feng, Jintao Hai (Beijing Research Institute of Mechanical & Electrical Technology, Beijing 100083, China Academy of Machinery Science and Technology, Beijing 100044, China) 机械部北京机械所北京 100083 机械部机械科学研究院北京 100044

A new method of getting ultrafine grain size has been investigated, which is called 'Extrusion Upsetting Multiple Processing in Sandglass Die' or 'Sandglass Extrusion' (SE). Since the shape of tested billet can remain unchanged after SE, the billet can be extruded repeatedly in order to get large plastic strain. The ultrafine grain size can be obtained in the billet material due to the large plastic strain and the dynamic recrystallization during SE. The experiments on SE of Zn-5% Al alloy have been done. The SE technology, microstructures, microhardness and superplasticity of tested material after SE have been studied. The experimental results show that the equal-axial ultrafine microstructures can be introduced to the bulk test material during sandglass extrusion. The high strain rate superplasticity can be realized.

关键词： sandglass extrusion ultrafine grain large plastic strain superplasticity Zn-Al alloy