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Heterogeneous fiberous structured Mg-Zn-Zr alloy with superior strength-ductility synergy

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Journal of materials Science & Technology 2023年第3期134卷 67-80页

作者： Wei Fu Pengfei Dang Shengwu Guo Zijun Ren Daqing Fang Xiangdong Ding Jun Sun State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China

Here we reported a heterogeneous fiberous structured Mg-5.6Zn-0.6Zr(wt%)alloy obtained by conventional extrusion method,which exhibited high yield strength of∼345 MPa,ultimate tensile strength of∼370 MPa,and high tensile strain of∼20.5%,superior to most of the Mg-Zn based alloys reported so far.The extraordinarily high mechanical properties were mainly attributed to the heterogeneous fiberous structure consisting of alternating coarse-and fine-grain layers.Grains in the different layers grew into the neighboring layers,ensuring a good layer bonding.A high Schmid factor and geometric compatibility factor for pyramidal slip led to full slip transfer between the neighboring coarse grains and fine grains,which could help to release the stress concentration and avoid early fracture.The profuse acti-vatedglide dislocations could render the unprecedented high tensile strain.The constraint by the hard fine-grain domains made the soft coarse-grain domains strong like the hard fine-grain domains,as well as the nanoscale precipitates pinning dislocations,contributed to the high strength.The hetero-geneous microstructure design was shown to have synergistic improvement in strength-ductility balance,which could be an inspiring strategy to improve mechanical properties of hexagonal close-packed(hcp)metals.

关键词： ZK60 Mg alloy Heterogeneous fiberous structure High strength-ductility synergy Pyramidal dislocations Bimodal grain sizes

Synergistic effects of 1T MoS_(2)and interface engineering on hollow NiCoP nanorods for enhanced hydrogen evolution activity

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Journal of materials Science & Technology 2023年第14期145卷 165-173页

作者： Qiaomei Luo Lan Sun Yiwei Zhao Chen Wang Hongqiang Xin Danyang Li Fei Ma State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China

Metallic 1T-phase molybdenum disulfide(1T-MoS_(2))shows more excellent electrocatalytic performance for hydrogen evolution reaction(HER)than semiconducting 2H-phase MoS_(2)(2H-MoS_(2)).Therefore,the facile controllable synthesis of hierarchical structure with rich 1T-MoS_(2)is desired for highly efficient electrocatalytic performance.In this work,a simple solvothermal method is proposed to fabricate hol-low NiCoP/MoS_(2)-V heterostructure with 63.2%1T-MoS_(2),in which the abundant catalytic active sites are exposed,the mass transfer properties are improved,and the electronic states are optimized.Moreover,the low energy difference between 2H and 1T phases and near zero free energy of hydrogen adsorption(△G H∗)result in fast kinetics and excellent catalytic performances.Specifically,the NiCoP/MoS_(2)-V com-posite exhibits enhanced HER activity with a low overpotential of 74.6 mV at 10 mA cm^(-2)and superior stability in alkaline electrolytes.This efficient design opens up new vistas for developing high-activity electrocatalysts.

关键词： Hollow hierarchical structure 1T-MoS_(2) Heterointerface Optimized electronic states Synergistic effect Superior HER activity

A unified model for ductile-to-brittle transition in body-centered cubic metals

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Journal of materials Science & Technology 2023年第10期141卷 193-198页

作者： Yu-Heng Zhang En Ma Jun Sun Wei-Zhong Han State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China

Ductile-to-brittle transition(DBT)is a well-known phenomenon in body-centered-cubic(BCC)metals,in-termetallics and semiconductor materials.A quantitative prediction of the DBT temperature,however,has so far remained intractable.Here,we propose a unified model based on the efficacy of dislocation multi-plication as the controlling factor for DBT,with the dislocation source efficiency governed by the relative mobility of screw versus edge dislocations.The model successfully predicts the DBT temperature of iron,molybdenum and tungsten,and also covers the influence of grain size,initial dislocation density,and the multiplicity of dislocation sources.A comparison with experiments indicates that the model captures the key DBT features,providing new insight into the toughness of BCC metals.

关键词： Metals Ductile Brittle Dislocation Mobility

Bifunctional SiC/Si_(3)N_(4) aerogel for highly efficient electromagnetic wave absorption and thermal insulation

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Journal of Advanced Ceramics 2023年第2期12卷 309-320页

作者： Lei WANG Zhixin CAI Lei SU Min NIU Kang PENG Lei ZHUANG Hongjie WANG State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China

SiC ceramics are attractive electromagnetic(EM)absorption materials for the application in harsh environment because of their low density,good dielectric tunable performance,and chemical stability.However,the performance of current SiC-based materials to absorb EM wave is generally unsatisfactory due to poor impedance matching.Herein,we report ultralight SiC/Si3N4 composite aerogels(~15 mg·cm^(−3))consisting of numerous interweaving SiC nanowires and Si3N4 nanoribbons.Aerogels were prepared via siloxane pyrolysis and chemical vapor reaction through the template method.The optimal aerogel exhibits excellent EM wave absorption properties with a strong reflection loss(RL,−48.6 dB)and a wide effective absorption band(EAB,7.4 GHz)at a thickness of 2 mm,attributed to good impedance matching and multi attenuation mechanisms of waves within the unique network structure.In addition,the aerogel exhibits high thermal stability in air until 1000℃and excellent thermal insulation performance(0.030 W·m^(−1)·K^(−1)).These superior performances make the SiC/Si_(3)N_(4) composite aerogel promising to become a new generation of absorption material served under extreme conditions.

关键词： bicontinuous network SiC nanowires impedance matching electromagnetic(EM)wave absorption extreme conditions

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

Unusual He-ion irradiation strengthening and inverse layer thickness-dependent strain rate sensitivity in transformable high-entropy alloy/metal nanolaminates:A comparison of Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu vs Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu

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Journal of materials Science & Technology 2022年第21期116卷 199-213页

作者： Y.F.Zhao H.H.Chen D.D.Zhang J.Y.Zhang Y.Q.Wang K.Wu G.Liu J.Sun State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China

In this work,we prepare transformable HEA/Cu nanolaminates(NLs)with equal individual layer thick-ness(h)by the magnetron sputtering technique,i.e.,Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu and Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu,and comparatively study He-ion irradiation effects on their microstructure and mechanical properties.It ap-pears that the as-deposited HEA/Cu NLs manifest two size h-dependent hardness regimes(i.e.,increased hardness at small h and hardness plateau at large h),while the He-implanted ones exhibit monotonically increased hardness.Contrary to the fashion that smaller h renders less irradiation hardening in bimetal NLs,the Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs manifest the trend that smaller h leads to greater irradiation hard-ening.By contrast,the Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu NLs exhibit the maximum irradiation hardening at a critical h=50 nm.Below this critical size,smaller h results in lower radiation hardening(similar to bimetal NLs),while above this size,smaller h results in greater radiation hardening(similar to Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs).Moreover,these transformable HEA/Cu NLs display inverse h-dependent strain rate sensitivity(SRS m)before and after He-ion irradiation.Nevertheless,compared with as-deposited samples,the irradi-ated Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs display reduced SRS,while the irradiated Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu NLs dis-play enhanced SRS.Such unusual size-dependent irradiation strengthening and inverse h effect on SRS in irradiated samples were rationalized by considering the blocking effects of He bubbles on dislocation nucleation and motion,i.e.,dislocations shearing or bypassing He bubbles.

关键词： High entropy alloy/metal nanolaminates Interfaces Irradiation hardening Strain rate sensitivity Size effects

铝合金中Portevin-Le Chatelier效应研究概述:内在机理及微观调控

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Journal of Central South University 2022年第3期29卷 744-766页

作者：张鹏刘刚孙军 State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China

在应力作用下金属材料的塑性失稳现象对构件的安全服役至关重要,这也一直是科学和工程领域关心的重要问题之一。铝合金作为应用广泛的轻质金属结构材料,普遍存在由Portevin-Le Chatelier(PLC)效应引起的塑性失稳现象。不同于结构设计和... 详细信息

在应力作用下金属材料的塑性失稳现象对构件的安全服役至关重要,这也一直是科学和工程领域关心的重要问题之一。铝合金作为应用广泛的轻质金属结构材料,普遍存在由Portevin-Le Chatelier(PLC)效应引起的塑性失稳现象。不同于结构设计和应力状态导致的屈曲失稳,PLC效应是材料的本征特性,起源于可动溶质原子反复钉扎位错与位错脱钉扎之间的动态交互作用;宏观表现为,在特定的应变速率和温度区间内,局部变形带会突发形核并迅速扩展,在应力−应变曲线上对应出现应力波动。通常,PLC效应导致的应力波动幅值有限,但与其伴生的负应变速率敏感性会降低材料延性,且局部滑移特性会破坏钣金成形金属的表面质量,在汽车蒙皮等注重外观的应用中须加以规避。因此,探索铝合金中PLC效应的微观机理,以及如何通过微观结构人为调控PLC效应,具有重要的意义。本文对PLC效应及其微观机理进行概括性的介绍,并总结了铝合金中两种主要微观结构调控方式(析出调控和细晶调控)对于PLC效应的作用规律。需特别指出,作为新型的强化原子结构,高密度的溶质团簇不仅可以打破强度—延性的倒置关系,还展现出比析出相更为有效的PLC效应抑制作用。

关键词：铝合金 PLC效应动态应变时效析出相晶粒尺寸

High-entropy Sm_(2)B_(2)O_(7)(B=Ti,Zr,Sn,Hf,Y,Yb,Nb,and Ta) oxides with highly disordered B-site cations for ultralow thermal conductivity

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Journal of materials Science & Technology 2022年第24期119卷 182-189页

作者： Liang Xu Lei Su Hongjie Wang Hongfei Gao Pengfei Guo Min Niu Kang Peng Lei Zhuang Zhiwei Dai State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China

materials with ultralow thermal conductivity and good thermal stability are of great interest in numerous applications such as energy storage and conversion devices,and thermal insulation components.In this work,a family of high-entropy Sm_(2)B_(2)O_(7)(B=Ti,Zr,Sn,Hf,Y,Yb,Nb,and Ta) oxides with highly disordered cations on the B-site has been synthesized by introducing large atomic-size mismatch,mass and charge disorder.Through tuning the composition,the high-entropy Sm_(2)B_(2)O_(7) oxides can be engineered from pyrochlore to fluorite structure,accompanied with an order-disorder transition.The pyrochlore Sm_(2)(Nb_(0.2)Sn_(0.2)Ti_(0.2)Y_(0.2)Zr_(0.2))_(2)O_(7) and fluorite Sm_(2)(Nb_(0.2)Ta_(0.2)Y_(0.2)Yb_(0.2)Zr_(0.2))_(2)O_(7) exhibit low thermal conductivities of 1.35 W·m^(-1)·K^(-1) and 1.23 W·m^(-1)·K^(-1),respectively,indicating their good thermal insulation.In addition,the high-entropy fluorite Sm_(2)(Nb_(0.2)Ta_(0.2)Y_(0.2)Yb_(0.2)Zr_(0.2))_(2)O_(7) also shows average thermal expansion coefficient of 10.2 × 10^(-6)℃^(-1) and high-temperature stability even after thermal exposure at 1600 °C in air for 30 h.These results indicate that the high-entropy Sm_(2)B_(2)O_(7)(B=Ti,Zr,Sn,Hf,Y,Yb,Nb,and Ta) can be promising candidates for thermal barrier coatings and thermally insulators.

关键词： High-entropy oxides Atomic sizes mismatch Mass and charge disorder Thermal conductivity Thermal barrier coatings materials

Designing hetero-structured ultra-strong and ductile Zr-2.5Nb alloys:Utilizing the grain size-dependent martensite transformation during quenching

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Journal of materials Science & Technology 2022年第30期125卷 198-211页

作者： S.Y.Liu J.Y.Zhang J.Kuang X.Y.Bao D.D.Zhang C.L.Zhang J.K.Yang G.Liu J.Sun State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China

To further improve the service performance of Zr-2.5Nb alloy worked as pressure tubes in pressurized heavy water reactors,more investigation about the microstructure and thermomechanical processing route of Zr-2.5Nb alloy need to be conducted.In this work,a hetero-structured Zr-2.5Nb alloy was prepared by applying a novel technique.Microstructure analysis reveals that the alloy exhibits a grain sizedependent martensite substructure transition during post-rolling quenching.The hetero-structure consists of equiaxed primaryαgrains and the lamellae groups containing both parallelα’dislocation martensite andα’twin martensite.Compared with the previously reported Zr-Nb alloys,the present Zr-2.5Nb alloys manifest the highest yield strength(∼710 MPa),together with a high ultimate tensile strength(∼844 MPa)and good ductility(∼17.1%).The enhanced mechanical properties are found to arise from the properly controlled fraction/size of the two types of martensite,which not only significantly strengthens the alloy but also contributes to a stronger strain hardening.A model based on the grain-size-dependent critical resolved shear stress for dislocation slip and twinning has been proposed to explain theα’martensite substructures transition at a critical grain size dc=3.3μm.Below this size,the critical resolved shear stress(CRSS)for twinning is higher than that for theslip.Thus,theα’dislocation martensite is more favorable to form.Otherwise,theα’twin martensite would exhibit a high activity.The present work indicates that making use of the grain size-dependent martensite transformation to tailor the heterostructure in Zr alloys is an effective strategy to overcome the strength–ductility trade-off in the material.

关键词： Zr-Nb alloys Heterogeneous structure Martensitic transformation Grain size Strength