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Regulation of bimodal structure and mechanical properties of powder-thixoformed GO/ZK60 magnesium matrix composite through adjusting GO content

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Journal of Materials Science & Technology 2023年第31期162卷 74-89页

作者： Lingyun Wang Tijun Chen State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals Lanzhou University of TechnologyLanzhou 730050China

Although remarkable strength enhancements can be achieved in graphene oxide(GO)/graphene nanoplatelets(GNPs)reinforced Mg matrix composites by using the available techniques,their ductility is always quite poor due to the difficultly avoided strength-ductility trade-off.To conquer this dilemma,GO/ZK60 composites with bimodal-grain structure were fabricated using powder thixoforming in this work.The results indicate that the grain size and volume fraction of coarse grains(CGs)first decrease as the GO content increases to 0.2 wt.%and then increase again as the content increases to 0.3 wt.%,while the grain size in the fine grains(FGs)almost does not change.Consequently,the strength of the composites is improved with increasing GO content and reaches the peak values at the content of 0.2 wt.%.The composite with 0.1 wt.%GO content exhibits significantly increased tensile yield strength up to 177±2 MPa while maintaining a high elongation of 23.1%±2.5%,being equivalent to that of the ZK60 matrix alloy.The increased FGs volume fraction,together with the promoted dislocation accumulation and storage via GO and grain refinement of large-sized CGs lead to the improvement of strain hardening ability,thus rendering the composite an excellent ductility.Furthermore,the deformation of the GO/ZK60 composites occurs progressively from the FGs to the CGs,which is opposite to the status of the milled ZK60 matrix alloy.In view of the microstructure characteristics of the composites,a new complex calculation model was proposed and it could well predict the strength of the bimodal GO/ZK60 composites.This study provides a new insight into the microstructure design and fabrication technology of GO/GNPs reinforced metal-based composites with high strength and ductility.

关键词： Graphene oxide bimodal structure Magnesium matrix composites Mechanical properties Powder thixoforming

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Simultaneous enhancement of strength and ductility in friction stir processed 2205 duplex stainless steel with a bimodal structure:experiments and crystal plasticity modeling

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Science China(Physics,Mechanics & Astronomy) 2022年第2期65卷 66-81页

作者： Yanying Hu Zexin Fang Yongbing Peng Weiqi Yang Xianfeng Ma Jinglong Li Yunqiang Zhao Biao Wang Sino-French Institute of Nuclear Engineering and Technology Sun Yat-Sen UniversityZhuhai 519082China State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi'an 710072China Guangdong Provincial Key Laboratory of Advanced Welding Technology China-Ukraine Institute of WeldingGuangdong Academy of SciencesGuangzhou 510650China

Achieving excellent strength-ductility synergy is a long-lasting research theme for structural materials.However,attempts to enhance strength usually induce a loss of ductility,i.e.,the strength-ductility trade-off.In the present study,the strength-ductility trade-off in duplex stainless steel(DSS)was overcome by developing a bimodal structure using friction stir processing(FSP).The ultimate tensile strength and elongation were improved by 140%and 109%,respectively,compared with those of the asreceived materials.Plastic deformation and concurrent dynamic recrystallization(DRX)during FSP were responsible for the formation of bimodal structure.Incompatible deformation resulted in the accumulation of dislocations at the phase boundaries,which triggered interpenetrating nucleation between the austenite and ferrite phases during DRX,leading to a bimodal structure.The in situ mechanical responses of the bimodal structure during tensile deformation were investigated by crystal plasticity finite element modeling(CPFEM).The stress field distribution obtained from CPFEM revealed that the simultaneous enhancement of strength and ductility in a bimodal structure could be attributed to the formation of a unique dispersion-strengthened system with the austenite and ferrite phases.It is indicated that the present design of alternating fine austenite and coarse ferrite layers is a promising strategy for optimizing the mechanical properties of DSSs.

关键词： friction stir processing duplex stainless steel bimodal structure tensile strength crystal plasticity

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Tension-compression asymmetry and corresponding deformation mechanism in ZA21 magnesium bars with bimodal structure

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International Journal of Minerals,Metallurgy and Materials 2023年第1期30卷 92-103页

作者： Yujiao Wang Yun Zhang Haitao Jiang Institute of Engineering Technology University of Science and Technology BeijingBeijing 100083China Beijing Institute of Machinery and Equipment Beijing 100854China

We investigated the asymmetric tension-compression(T-C)behavior of ZA21 bars with bimodal and uniform structures through axial tension and compression tests.The results show that the yield strengths of bars having bimodal structure are 206.42 and 140.28 MPa under tension and compression,respectively,which are higher than those of bars having uniform structure with tensile and compressive yield strength of 183.71 and 102.86 MPa,respectively.Prismatic slip and extension twinning under tension and basal slip and extension twinning under compression dominate the yield behavior and induce the T-C asymmetry.However,due to the basal slip activated in fine grains under tension and the inhibition of extension twinning by fine grains under compression,the bimodal structure possesses a lower T-C asymmetry(0.68)compared to the uniform structure(0.56).Multiple extension twins occur during deformation,and the selection of twin variants depends on the Schmid factor of the six variants activated by parent grains.Furthermore,the strengthening effect of the bimodal structure depends on the grain size and the ratio of coarse and fine grains.

关键词： bimodal structure deformation mechanism Hall-Petch relationship tension-compression asymmetry twin variant selection

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High strength and ductility Mg-8Gd-3Y-0.5Zr alloy with bimodal structure and nano-precipitates

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Journal of Materials Science & Technology 2020年第9期44卷 19-23页

作者： Xiaoxiao Wei Li Jin Fenghua Wang Jing Li Nan Ye Zhenyan Zhang Jie Dong National Engineering Research Center of Light Alloy Net Forming&State Key Laboratory of Metal Matrix Composites Shanghai Jiao Tong UniversityShanghai 200240China Powder Metallurgy Research Institute Central South UniversityChangsha 410083China

To resolve the strength-ductility trade-off problem for high-strength Mg alloys,we prepared a high performance Mg-8Gd-3Y-0.5 Zr(wt%)alloy with yield strength of 371 MPa,ultimate tensile strength of 419MPa and elongation of 15.8%.The processing route involves extrusion,pre-deformation and aging,which leads to a bimodal structure and nano-precipitates.Back-stress originated from the deformationincompatibility in the bimodal-structure alloy can improve ductility.In addition,dislocation density in coarse grains increased during the pre-deformation strain of 2%,and the dislocations in coarse grains can promote the formation of chain-like nano-precipitates during aging treatment.The chain-like nanoprecipitates can act as barriers for dislocations slip and the existing mobile dislocations enable good ductility.

关键词： Magnesium alloy Strength-ductility trade-off bimodal structure Back-stress Chain-like intragranular nano-precipitates

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Deformation Mechanism of bimodal structured 2205 Duplex Stainless Steel in Two Yield Stages

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Journal of Wuhan University of Technology(Materials Science) 2023年第1期38卷 184-191页

作者：盛捷 DU Mingchen LI Yufeng MA Guocai CHEN Weiqian ZHENG Yuehong ZHAN Faqi REN Junqiang G I Raab 喇培清 State Key Laboratory of Gansu Advanced Non-Ferrous Metal Materials Lanzhou University of TechnologyLanzhou 730050China Jiuquan Iron and Steel(Group)Co. Ltd.Jiayuguan 735100China Key Laboratory of Solar Power System Engineering Jiuquan Vocational and Technical CollegeJiuquan 735000China Institute of Physics of Advanced Materials Ufa State Aviation Technical University12 K.Marx StreetUfa 450008Russia

A kind of micro/nanostructured 2205 duplex stainless steel(DSS)with uniform distribution of nanocrystals was prepared via aluminothermic reaction method.The analysis of stress-strain curve showed that the fracture strength and elongation of the specimen were 946 MPa and 24.7%,respectively.At present,the research on microstructure of bimodal 2205 DSS at room temperature(RT)mainly depended on scanning electron microscope(SEM)observation after loading experiments.The test result indicates that there are two different yield stages in stress-strain curve of specimen during tensile process.The microstructure of duplex bimodal structured stainless steel consists of two pairs of soft hard regions and phases.By studying deformation mechanism of bimodal structured stainless steel,the interaction between soft phase and hard phase are discussed.The principle of composition design and microstructure control of typical duplex stainless steel is obtained,which provides an important research basis for designing of advanced duplex stainless steel.

关键词： 2205 duplex stainless steel bimodal structure in-situ tensile test deformation mechanism two different yield stages

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Low-cycle fatigue behaviour of Mg-9Gd-4Y-2Zn-0.5Zr alloys with different structures

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Journal of Magnesium and Alloys 2023年第9期11卷 3382-3393页

作者： Jinsheng Ji Jie Zheng Leichen Jia Yong Zhang Yunfei Jia Yusha Shi Heng Zhang Yong Xue School of Materials Science and Engineering North University of ChinaTaiyuan 030051China Key Laboratory of Pressure Systemsand Safety Ministry of EducationSchool of Mechanical and Power EngineeringEast China University of Science and TechnologyShanghai 200237China

The strain-controlled cyclic deformation behaviour of Mg-9Gd-4Y-2Zn-0.5Zr with different structures was investigated. Alloys were prepared by solution, extrusion and pre-ageing extrusion, and the microstructures before and after the fatigue tests were characterized.Experimental results indicated that the bimodal structure owned the better performance in fatigue test, which was attributed to the higher yield strength. For the equiaxed structure, cyclic hardening induced stress concentration until the failure. Stable cyclic deformation and persistent cyclic softening played an important role at the low and high strain amplitudes, respectively. This was attributed to the formation of fine grains relieving the stress concentration during cyclic loading. In addition, residual twins were observed in equiaxed structure to induce crack, and the bimodal structure effectively restrain it.

关键词： Strain-controlled fatigue bimodal structure Fractography Mg-Gd-Y-Zn-Zr alloy

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