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Acta Metallurgica Sinica(English Letters) 2024年第1期37卷 78-88页

作者： Leilei Li Kaikai Song Qingwei Gao Changshan Zhou Xiaoming Liu Yaocen Wang Xiaojun Bai Chongde Cao School of Physical Science and Technology Northwestern Polytechnical UniversityXi’an710016China Weihai Research Institute of Industrial Technology Shandong UniversityWeihai264209China Research and Development Institute of Northwestern Polytechnical University in ShenzhenShenzhen518057China

The L1_(2)-strengthened Co_(34)Cr_(32)Ni_(27)Al_(4)Ti_(3)medium-entropy alloy(MEA)with precipitations of grain boundaries has been developed through selective laser melting(SLM)followed by cold rolling and annealing,exhibiting excellent strength-ductility synergy.The as-printed alloy exhibits low yield strength(YS)of~384 MPa,ultimate tensile strength(UTS)of~453 MPa,and uniform elongation(UE)of 1.5%due to the existence of the SLM-induced defects.After cold rolling and annealing,the YS,UTS,and UE are significantly increased to~739 MPa,~1230 MPa,and~47%,respectively.This enhancement primarily originates from the refined grain structure induced by cold rolling and annealing.The presence of coherent sphericalγ'precipitates(L1_(2)phases)and Al/Ti-rich precipitates at the grain boundaries,coupled with increased lattice defects such as dislocations,stacking faults,and ultrafine deformation twins,further contribute to the property’s improvement.Our study highlights the potential of SLM in producing high-strength and ductile MEA with coherent L1_(2)nanoprecipitates,which can be further optimized through subsequent rolling and annealing processes.These findings offer valuable insights for the development of high-performance alloys for future engineering applications.

关键词： medium-entropy alloy Selective laser melting Precipitation Strength Ductility

Superb strength and ductility balance of a Co-free medium-entropy alloy with dual heterogeneous structures

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Journal of Materials Science & Technology 2022年第3期98卷 197-204页

作者： Wenjie Lu Kang Yan Xian Luo Yuetang Wang Le Hou Pengtao Li Bin Huang Yanqing Yang State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Langu Institute for Materials Analysis Co.Ltd Weihai 264207China Institute of optics and electronics Chinese Academy of SciencesChengdu 610200China

In present work,we successfully fabricated a novel Co-free non-equiatomic Ni_(46)Cr_(23)Fe_(23)Al_(4)Ti_(4)mediumentropy alloy with dual heterogeneous structures,i.***.three-levels grain structures and heterogeneous L1;precipitates.Experimental results revealed the dual heterogeneous structures lead to remarkable strength-ductility synergy properties in this Co-free medium-entropy alloy,showing high yield strength and ultimate tensile strength of~1203 MPa and~1633 MPa,respectively,remaining an excellent ductility of~28.7%.Further analyses about strengthening and deformation mechanisms indicated precipitation hardening and hetero-deformation induced hardening contribute the majority strength enhancement,meanwhile deformation-induced hierarchical stacking-faults networks,high density Lomer-Cottrell locks and microstructure features of heterogeneous grains and precipitates substantially facilitate the high work-hardening capacity and excellent tensile ductility.This work not only offers fundamental understanding of the strength and deformation mechanisms of the dual heterogeneous structural material,but also provides useful strength design strategy for low-price high performance high/medium-entropy alloys.

关键词： Dual heterogeneous structures medium-entropy alloy Co-free Strength-ductility synergy properties

Mechanical property comparisons between CrCoNi medium-entropy alloy and 316 stainless steels

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Journal of Materials Science & Technology 2022年第13期108卷 256-269页

作者： Xiaoru Liu Hao Feng Jing Wang Xuefei Chen Ping Jiang Fuping Yuan Huabing Li En Ma Xiaolei Wu State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Science University of Chinese Academy of SciencesBeijing 100049China School of Metallurgy Northeastern UniversityShenyang 110819China Center for alloy Innovation and Design(CAID) State Key Laboratory for Mechanical Behavior of MaterialsXi'an Jiaotong UniversityXi’an 710049China

We systematically compared the mechanical properties of CrCoNi,a recently emerged prototypical medium-entropy alloy(MEA)with face-centered-cubic(FCC)structure,with hallmark FCC alloys,in particular,the well-known austenitic 316 L and 316 LN stainless steels,which are also concentrated singlephase FCC solid solutions and arguably next-of-kin to the MEAs.The tensile and impact properties,across the temperatures range from 373 K to 4.2 K,as well as fracture toughness at 298 K and 77 K,were documented.From room temperature to cryogenic temperature,all three alloys exhibited similarly good mechanical properties;CrCoNi increased its tensile uniform elongation and fracture toughness,which was different from the decreasing trend of the 316 L and 316 LN.On the other hand,the stainless steels showed higher fracture toughness than CrCoNi at all temperatures.To explain the differences in macroscopic mechanical properties of the three alloys,microstructural hardening mechanisms were surveyed.CrCoNi MEA relied on abundant mechanical twinning on the nanoscale,while martensitic transformation was dominant in 316 L at low temperatures.The deformation mechanisms in the plastic zone ahead of the propagating crack in impact and fracture toughness tests were also analyzed and compared for the three alloys.

关键词： medium-entropy alloy Austenite stainless steel Strain hardening Ductility Fracture toughness Charpy impact toughness

Microstructure and mechanical properties of transient liquid phase bonding DD5 single-crystal superalloy to CrCoNi-based medium-entropy alloy

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Journal of Materials Science & Technology 2022年第1期96卷 140-150页

作者： Shiwei Li Jinglong Li Junmiao Shi Yu Peng Xuan Peng Xianjun Sun Feng Jin Jiangtao Xiong Fusheng Zhang State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Shaanxi Key Laboratory of Friction Welding Technologies Northwestern Polytechnical UniversityXi’an 710072China

This study focuses on the transient liquid phase(TLP)bonding of DD5 single-crystal superalloy to Cr Co Nibased medium-entropy alloy(MEA)using a BNi-2 filler alloy.The microstructure and mechanical properties of the TLP-bonded DD5/MEA joint were evaluated,and the microstructural evolution mechanism was investigated.The formation of the isothermal solidification zone(ISZ)depended on the diffusion of the melting-point depressants(Si and B elements)from the liquid filler into the DD5 and MEA substrates,as well as the dissolution of the substrates.Boron diffused along theγchannel of DD5 and reacted to form M_(5)B_(3)boride,herein referred to as the diffusion-affected zone(DAZ I).Similarly,the Cr_(5)B_(3)boride precipitated in the Ni-rich MEA matrix adjacent to the MEA substrate(i.e.,DAZ II).Additionally,a coherent orientation of[0]_(BCY)//[011]_(FCC)and(002)_(BCY)//(200)_(FCC)was detected between M_(5)B_(3)boride with a body-centered tetragonal(BCT)structure and the face-centered cubic(FCC)matrix.The performance of the joint was dominated by the properties of the bonding seam.As the bonding time increased from 20to 80 min,the athermal solidification zone(including eutectic microstructure)was gradually replaced by the ISZ exhibiting excellent plastic deformation capability,and the shear strength of the joint was improved.The maximum shear strength(752 MPa)was achieved when the eutectic-free joint was bonded at 1050℃ for 80 min.The fracture morphology revealed a mixture mode,indicating the initiation of cracks in the DAZ II,mainly propagating in the ISZ,and passing through the DAZ I.

关键词： Microstructure Mechanical properties Transient liquid phase bonding Single-crystal superalloy medium-entropy alloy

Extremely strong coupling s-wave superconductivity in the medium-entropy alloy TiHfNbTa

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Science China(Physics,Mechanics & Astronomy) 2023年第7期66卷 127-135页

作者： Lingyong Zeng Xunwu Hu Mebrouka Boubeche Kuan Li Longfu Li Peifeng Yu Kangwang Wang Chao Zhang Kui Jin Dao-Xin Yao Huixia Luo School of Materials Science and Engineering State Key Laboratory of Optoelectronic Materials and TechnologiesKey Lab of Polymer Composite&Functional MaterialsGuangdong Provincial Key Laboratory of Magnetoelectric Physics and DevicesSun Yat-Sen UniversityGuangzhou 510275China Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices Center for Neutron Science and TechnologySchool of PhysicsSun Yat-Sen UniversityGuangzhou 510275China Songshan Lake Materials Laboratory University Innovation TownDongguan 523808China Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Key Laboratory of Vacuum Physics School of Physical SciencesUniversity of Chinese Academy of SciencesBeijing 100049China

Here we report a TiHfNbTa bulk medium-entropy alloy(MEA)superconductor crystallized in the body-centered cubic structure with the unit cell parameter a=3.35925?,which is synthesized by an arc melting method.Superconducting properties of the TiHfNbTa are studied by employing magnetic susceptibility,resistivity,and specific heat measurements.Experimental results show a bulk superconducting transition temperature(Tc)of around 6.75 K.The lower and upper critical fields for TiHfNbTa are45.8 m T and 10.46 T,respectively.First-principles calculations show that the d electrons of Ti,Hf,Nb,and Ta are the main contribution to the total density of states near the Fermi level.Our results indicate that the superconductivity is a conventional swave type with extremely strong coupling(△C_(el)/γ_(n)T_(c)=2.88,2△_(0)/k_(B)T_(c)=5.02,and λ_(ep)=2.77).The extremely strong coupling behavior in the s-wave type Ti Hf Nb Ta MEA superconductor is unusual because it generally happens in cuprates,pnictides,and other unconventional superconductors.

关键词： medium-entropy alloy superconductivity s-wave type TiHfNbTa

Unveiling the grain boundary-related effects on the incipient plasticity and dislocation behavior in nanocrystalline CrCoNi medium-entropy alloy

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Journal of Materials Science & Technology 2022年第32期127卷 98-107页

作者： Shuo Sun Yang Yang Chenxu Han Guixun Sun Yan Chen Hongxiang Zong Jiangjiang Hu Shuang Han Xiaozhou Liao Xiangdong Ding Jianshe Lian Key Laboratory of Automobile Materials Ministry of EducationCollege of Materials Science and EngineeringJilin UniversityChangchun 130025China State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China College of Mechanical Engineering Zhejiang University of TechnologyHangzhou 310014China School of Aerospace Mechanical and Mechatronic EngineeringThe University of SydneySydneyNSW 2006Australia

The incipient plasticity and dislocation behavior in a nanocrystalline(NC)CrCoNi medium-entropy alloy were systematically investigated in terms of pop-in events during instrumental nano-indentation tests.Quantitative statistical analysis and molecular dynamic simulations were performed to reveal the effects of grain boundaries(GBs)on initial stages of plastic deformation.Multiple pop-in events appeared during loading on the NC CrCoNi.The first pop-in that represents the initial yielding was identified to be controlled by dislocation nucleation,which is in sharp contrast to the continuous elastic-plastic transition mediated by GB mechanisms in NC pure metals.This can be attributed to the sluggish kinetics of the chemically complex GBs(CCGBs)in the NC CrCoNi that hinders diffusive GB activities but facilitates dislocation nucleation.Subsequent pop-ins were also found to be closely related to the extra dragging effects imposed by the CCGBs on dislocation propagation in the NC alloy.Moreover,the extremely small grain sizes and the consequent high-volume fraction of GBs in the NC alloy severely restrict the lengths of dislocation source and the radii of dislocation loop,giving rise to a higher critical stress,smaller activation volume and lower pop-in width as compared with its coarse-grained counterpart.These results provide new insights into the onset of nano-plasticity in concentrated multi-principal element alloys.

关键词： medium-entropy alloy Nanocrystalline Nanoindentation Incipient plasticity Grain boundary

Effects of post annealing on the microstructure,precipitation behavior,and mechanical property of a(CoCrNi)_(94)Al_(3)Ti_(3)medium-entropy alloy fabricated by laser powder bed fusion

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Journal of Materials Science & Technology 2023年第4期135卷 142-155页

作者： Zhuang Li Pengcheng Zhao Tiwen Lu Kai Feng Yonggang Tong Binhan Sun Ning Yao Yu Xie Bolun Han Xiancheng Zhang Shantung Tu Key Laboratory of Pressure Systems and Safety Ministry of EducationSchool of Mechanical and Power EngineeringEast China University of Science and TechnologyShanghai 200237China Shanghai Key Laboratory of Materials Laser Processing and Modification School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China College of Automobile and Mechanical Engineering Changsha University of Science and TechnologyChangsha 410114China

The additive manufacturing of multi-principal element alloys has remarkable potential for industrial ap-plications.In this study,a(CoCrNi)_(94)Al_(3)Ti_(3)medium-entropy alloy(MEA)with adequate strength-ductility synergy was prepared via laser powder bed fusion.The microstructural evolution,mechanical property,and deformation mechanisms of the MEA were investigated after post annealing for a short period(0.5 h)at a temperature range of 773-1373 K using various microstructural characterization techniques and quantitative analysis.The static recrystallization temperature of the(CoCrNi)_(94)Al_(3)Ti_(3)MEA ranged from 973 to 1073 K.The average grain size first decreased and then increased,while the dislocation den-sity persistently decreased and texture gradually weakened with increasing annealing temperature.Cr-richσ-phase precipitates formed after 1073 K and then gradually dissolved at 1373 K,while Ni,Al,and Ti elements were aggregated to form a small amount of fine L1_(2)coherent precipitates with an aver-age diameter of approximately 70 nm at 1373 K.The evolution of the dislocation density,grain size,and precipitates significantly influenced the propensity of deformation twins and stacking faults,which consequently affected the strain hardening behavior and mechanical properties.The quantitative calcu-lation of strengthening mechanisms showed that dislocation strengthening played a dominant role at annealing temperatures below 1073 K,and it significantly weakened at 1373 K.Precipitation and grain boundary strengthening both markedly increased owing to the formation of precipitation particles and recrystallization-induced grain refinement after annealing at 1073 K.

关键词： medium-entropy alloy Additive manufacturing Heat treatment Strengthening mechanism Microstructural evolution

Dislocation glide and mechanical twinning in a ductile VNbTi medium entropy alloy

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Journal of Materials Science & Technology 2022年第15期110卷 210-215页

作者： Mingxu Wu Shubin Wang Fei Xiao Guoliang Zhu Chao Yang Da Shu Baode Sun Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming and State Key Lab of Metal Matrix Composites School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China

An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported.The screw dislocation glide,deformation twinning,and dislocation accumulation induced kink bands are identified as three deformation mechanisms that contribute to a large elongation above 20%.The{112}twins are activated at the beginning of the yield stage accompanied by sudden stress-drop and pronounced acoustic emission.Dislocations dominate subsequent tensile deformation,and the prevalent multiplanar dislocation slip promotes the formation of complex dislocation configurations(e.g.,debris,dipoles,and loops)and dense dislocation networks.The twin bands and kink bands can further impede the dislocation motion meanwhile effectively alleviate stress concentration.The synergistic activation of these deformation mechanisms provides new opportunities to design ductile refractory medium-and high-entropy alloys.

关键词： medium-entropy alloy Mechanical twinning Screw dislocation Multiplanar slip Tensile deformation

Excellent strength-ductility synergy properties of gradient nano-grained structural CrCoNi medium-entropy alloy

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Journal of Materials Science & Technology 2022年第17期112卷 195-201页

作者： Wenjie Lu Xian Luo Dou Ning Miao Wang Chao Yang Miaoquan Li Yanqing Yang Pengtao Li Bin Huang State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Langu Institute for Materials Analysis Co.Ltd Weihai 264207China School of Physics and Optoelectronic Engineering Yangtze UniversityJingzhou 434023China

Tailoring heterogeneities could bring out excellent strength-ductility synergy properties.A gradient nanograined(GNG)structure,i.***.grain size range from nanometer(~50 nm)at topest surface layer to micrometer(~1.3μm)at center layer,was successfully introduced into CrCoNi medium-entropy alloy(MEA)by means of high energy shot peening in this work.Experimental results demonstrated that this GNG CrCoNi MEA shows excellent strength and ductility combination properties,exhibiting high yield strength and ultimate tensile strength of~1215 MPa and~1524 MPa,respectively,while remaining a good ductility of~23.0%.The extraordinary hetero-deformation induced(HDI)hardening origins from heterogeneous structure,i.e.GNG structure,which contributes to the majority strength enhancement.Dynamical reinforced heterogeneous structure during tension process results in the enhanced HDI hardening effect,which facilitates excellent ductility and strain hardening capacity at high-level strength.Our work provide not only a feasible and effective way to strengthen the CrCoNi MEA,and other low stacking faults energy(SFE)materials,but also an useful insight to understanding HDI hardening in heterogeneous structure.

关键词： medium-entropy alloy Gradient nano-grained structure High energy shot peening Hetero-deformation induced hardening Strength-ductility synergy

A strong and ductile NiCoCr-based medium-entropy alloy strengthened by coherent nanoparticles with superb thermal-stability

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Journal of Materials Science & Technology 2023年第1期132卷 201-212页

作者： D.D.Zhang J.Kuang H.Xue J.Y.Zhang G.Liu J.Sun State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China

In this work,we designed a novel NiCoCr-based medium-entropy alloy(MEA)strengthened by coher-ent L12-nanoparticles,i.e.,(NiCoCr)92 Al 6 Ta 2(at.%).The strengthening and deformation mechanisms of the material and the coarsening kinetics of the coherent precipitates were systematically investigated.The results indicated that giant precipitation hardening and its synergy with other strengthening contributors confer on the aged material a yield strength as high as 1.0 GPa.Moreover,a unique particle-features-dependent plasticity mechanism was revealed in this alloy.That is,the alloy with a lower volume frac-tion,denser distribution,and finer particles mainly deformed by dislocation planar slip,otherwise,stack-faults-mediated plasticity was favored,rationalized by the cooperative/competitive effect of stack-fault energy,spatial confinement,and applied stress.Furthermore,the coarsening behavior of precipitate fol-lowed a modified Lifshitz-Slyozov-Wagner(LSW)model,and the nanoparticles displayed remarkably su-perior thermal stability compared to most traditional superalloys and reported multicomponent alloys.The superb coarsening resistance of precipitate originated from the coupled effect of intrinsic sluggish diffusion in multi-principal alloys and the dual-roles of Ta species as a precipitate stabilizer.This work provides a new pathway to develop strong-yet-ductile multicomponent alloys as promising candidates for high-temperature applications.

关键词： medium-entropy alloy Mechanical properties Precipitation hardening Deformation mechanisms Coarsening kinetics