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strengthening in Al-,Mo-or Ti-doped CoCrFeNi high entropy alloys:A parallel comparison

Journal of Materials Science & Technology 2021年第35期94卷 264-274页

作者： Xi Li Zhongtao Li Zhenggang Wu Shijun Zhao Weidong Zhang Hongbin Bei Yanfei Gao College of Materials Science and Engineering&Hunan Province Key Laboratory for Spray Deposition Technology and Application Hunan UniversityChangsha 410082China Department of Mechanical Engineering City University of Hong KongHong KongChina epartment of Materials Science and Engineering Center of Electron Microscopy and State Key Laboratory of Silicon MaterialsZhejiang UniversityHangzhou 310027China Department of Materials Science and Engineering University of TennesseeKnoxvilleTN 37996United States

In the current work,a parallel comparison of the influence of Al,Mo and Ti,on the microstructure and strengthening of the CoCrFeNi alloy was conducted.To achieve this,inconsistencies on variables including the extent of alloying,thermomechanical processing and property-evaluation method were avoided.Microstructurally,following cold-rolling,annealing of the 4 at.%Al-doped alloys at 800-1000℃ did not result in phase separation;nevertheless,that of the 4 at.%Mo-and Ti-doped alloys led to the respective formation ofσandηphase and,consequently,caused extra strengthening through the Orowan dislocation bypassing mechanism.Our systematic qualitative analysis and DFT calculations showed that Al and Ti are more effective than Mo in reducing the stacking fault energy(SFE)of the CoCrFeNi alloy,because they can induce more considerable deformation of electronic density,making the gliding of atomic layers easier.Following identical thermomechnical processing,Al-,Mo-,and Ti-doping causes different extent of solid solution strengthening and grain boundary strengthening.Mo causes the most pronounced solid solution strengthening but does not benefit the grain boundary strengthening;in contrast,the effectiveness of grain boundary strengthening is boosted by the doping Al and Ti.Current analyses support that Labusch instead of Fleischer mechanism is applicable to explain the differences in solid solution strengthening,and the observed differences in grain boundary strengthening arise from the different tendency of Al,Mo and Ti to reduce the SFE of CoCrFeNi.In addition,we determined the value of the dimensionless parameter f in the Labusch model for CoCrFeNi-based alloys and observed a close relation between Hall-Petch slope and SFE.Although more in-depth studies are needed to provide full and mechanistic understandings,both these findings in fact presents significant values toward designing novel singlephase high-strength CoCrFeNi-based alloys through manipulating the solid solution and grain boundary strengthening by compositional

关键词： CoCrFeNi alloy Compositional effect solid solution strengthening Grain boundary strengthening Precipitation strengthening Stacking fault energy

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A novel non-stoichiometric medium-entropy carbide stabilized by anion vacancies

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Journal of Materials Science & Technology 2020年第16期47卷 161-166页

作者： Chong Peng Hu Tang Yu He Xiaoqian Lu Peng jia Guoying Liu Yucheng Zhao Mingzhi Wang State Key Laboratory of Metastable Materials Science and Technology Yanshan UniversityQinhuangdao 066004China Center for High Pressure Science and Technology Advanced Research Beijing 100190China

Recently,high-entropy ceramics have attracted considerable attentions because of comprehensive physical and chemical properties of high hardness,fracture toughness,and conductivity.However,as a newly emerging class of materials,the synthesis,performance and applications of high-entropy ceramics are subject to further development.Here,we reported a new non-stoichiometric TiC0.4/WC/0.5Mo2C medium-entropy carbide(MEC)with a rock-salt structure.Attributed to the solid solution strengthening and twinning strengthening,the TiCO0.4/WC/0.5Mo2C sintered at 1900℃by spark plasma sintering(SPS)shows superior mechanical behaviors of microhardness(21.7 GPa),which exceeds that expected from the rule of mixture(ROM)of three individual metal carbides(19.1 GPa)and good fracture toughness(5.3 MPa m1/2).Significantly,the bulk synthesized via high-pressure and high-temperature(HPHT)sintering possesses smaller grain size and shows better comprehensive mechanical properties of microhardness(23.7 GPa)and fracture toughness(6.2 MPa m1/2).In addition,the effect of anion vacancies on the thermodynamic stability and synthesizability of TiC0.4/WC/0.5Mo2C was analyzed via quantitatively calculated entropy.Vacancies could significantly enhance the configuratio nal entropy of mixing of the solid phase.The introduction of vacancy defects may expand synthetic path for entropy-stabilized ceramics,especially for multi-component high tempe rature refractory ceramics.

关键词： Anion vacancies Medium-entropy carbide solid solution strengthening Twinning

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Ultrafine Grain Tungsten Heavy Alloys with Excellent Performance Prepared by Spark Plasma Sintering

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Journal of Wuhan University of Technology(Materials Science) 2020年第2期35卷 393-398页

作者： ZHANG Jingang WANG Weimin JI Wei HE Qianglong WANG Aiyang TAN Lin YANG Kai State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Institute of Material Science and EngineeringWuhan University of TechnologyWuhan 430070China

Ultrafine grain tungsten heavy alloys (WHAs) were successfully produced from the nano-crystalline powders using spark plasma sintering.The present study mainly discussed the effects of sintering temperature on the density,microstructure and mechanical properties of the alloys.The relative density of 98.12% was obtained at 1 050 ℃,and the tungsten grain size is about 871 nm.At 1 000 ℃-1 200 ℃,the mechanical properties of the alloys tend to first rise and then goes down.After SPS,the alloy exhibits improved hardness (84.3 HRA at 1 050 ℃) and bending strength (987.16 MPa at 1 100 ℃),due to the ultrafine-grained microstructure.The fracture mode after bending tests is mainly characterized as intergranular or intragranular fracture of W grains,interfacial debonding of W grains-binding phase and ductile tearing of binding phase.The EDS analysis reveals a certain proportion of solid solution between W and Ni-Fe binding phase.The good mechanical properties of the alloys can be attributed to grain refinement and solid solution strengthening.

关键词： tungsten heavy alloys ultrafine grain nano-crystalline powders solid solution strengthening spark plasma sintering

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