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Thermo-kinetic characteristics on stabilizing hetero-phase interface of metal matrix composites by crystal plasticity finite element method

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Journal of Materials Science & Technology 2024年第2期169卷 53-67页

作者： Y.B.Zhang S.J.Song F.Liu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Analytical&Testing Center Northwestern Polytechnical UniversityXi’an 710072China

Using dislocation-based constitutive modeling in three-dimension crystal plasticity finite element(3D CPFE)simulations,co-deformation and instability of hetero-phase interface in different material systems were herein studied for polycrystalline metal matrix composites(MMCs).Local stress and strain fields in two types of 3layer MMCs such as fcc/fcc Cu-Ag and fcc/bcc Cu-Nb have been predicted under simple compressive ***,more severe strain-induced interface instability can be observed in the fcc/bcc systems than in the fcc/fcc systems upon refining to metallic nanolayered composites(MNCs).By detailed analysis of stress and strain localization,it has been demonstrated that the interface instability is always accompanied by high-stress concentration,i.e.,thermodynamic characteristics,or high strain prevention i.e.,kinetic characteristics,at the hetero-phase *** then follows that the thermodynamic driving forceG and the kinetic energy barrier Q during dislocation and shear banding can be adopted to classify the deformation modes,following the so-called thermo-kinetic *** by inserting a high density of high-energy interfaces into the Cu-Nb composites,such thermo-kinetic integration at the hetero-phase interface allows a successful establishment of MMCs with the high△G-high Q deformation mode,which ensures high hardening and uniform strain distri-bution,thus efficiently suppressing the shear band,stabilizing the hetero-phase interface,and obtaining an exceptional combination in strength and *** hetero-phase interface chosen by a couple of thermodynamics and kinetics can be defined as breaking the thermo-kinetic correlation and has been proposed for artificially designing MNCs.

关键词： Thermodynamics and kinetics Physics-based constitutive modeling Hetero-phase interface Crystal plasticity finite element

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Effect of hot isostatic pressure on the microstructure and tensile properties of γ'-strengthened superalloy fabricated through induction-assisted directed energy deposition

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International Journal of Minerals,Metallurgy and Materials 2024年第5期31卷 1089-1097页

作者： Jianjun Xu Hanlin Ding Xin Lin Feng Liu Analytical&Testing Center Northwestern Polytechnical UniversityXi’an 710072China State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China

The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core *** HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly *** further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained *** comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ ***,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.

关键词： directed energy deposition Ni-based superalloys high-temperature preheating hot isostatic pressing microstructure tensile properties

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Nucleation/growth design by thermo-kinetic partition

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Journal of Materials Science & Technology 2023年第24期155卷 72-81页

作者： Feng Liu Analytical & Testing Center Northwestern Polytechnical University Xi'an Shaanxi 710072 China State Key Lab. of Solidification Processing Northwestern Polytechnical University Xi'an Shaanxi 710072 China

Departing from nucleation and growth involved in phase transformations (PTs) and/or plastic deformations (PDs), thermodynamics, kinetics, and thermo-kinetic partition are described. It has been shown that the thermo-kinetic partition reflects the scale of the so-called thermo-kinetic correlation, and by combining with the reference state of PT or PD, corresponds to so-called generalized stability. Regarding the universality of nucleation/growth and thermo-kinetic partition, the principle of high thermodynamic driving force-high generalized stability has been reinterpreted by integrating nucleation and growth, separating nucleation and growth, and designing so-called negative driving forces, respectively. As such, the current materials design is classified, summarized, and prospected. This work is helpful to realize high strength and high plasticity by designing nucleation and growth.

关键词： Nucleation Growth Thermo-kinetic partition

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Optimizing mechanical properties of magnesium alloys by philosophy of thermo-kinetic synergy:Review and outlook

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Journal of Magnesium and Alloys 2022年第2期10卷 346-383页

作者： Tianle Wang Feng Liu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’anShaanxi 710072China Analytical&Testing Center Northwestern Polytechnical UniversityXi’anShaanxi 710072China

Although several strategies(including grain refinement,texture adjustment,precipitation hardening,etc.)have been verified to effectively improve the mechanical properties of lightweight magnesium(Mg)alloys,considerable efforts are still needed to be made to comprehensively understand the potential mechanisms controlling complex microstructures and deformation behaviors exhibited by the hexagonal close-packed host lattice of Mg,thus assisting the rational design of materials at a more physical *** the cornerstone of this review,a universal rule,the so-called synergy of thermodynamics and kinetics(i.e.,thermo-kinetic diversity,correlation and connectivity),including a recently proposed theory of generalized stability(GS),is introduced to deepen our understanding on common behaviors in Mg alloys(i.e.,deformations(slip and twining modes),phase transformations(especially for precipitations)and interactions in between)at a new *** by the GS theory,typical cases for Mg alloys design are qualitatively evaluated to reemphasize the traditional strengthening and toughening strategies mentioned above and to illuminate their exquisite coordination for breaking through the trade-off relationship between strength and ductility,corresponding to a typical thermo-kinetic pair(i.e.,high driving force(ΔG)-high GS).To produce the Mg alloys with superior strength-ductility balances,the potential capacity of this GS theory for guiding processing path design is discussed,finally。

关键词： Magnesium alloys Synergy of thermodynamics and kinetics Generalized stability Superior strength-ductility balance

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Materials design by generalized stability

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Journal of Materials Science & Technology 2023年第16期147卷 153-164页

作者： Yu Zhang Haoran Peng Linke Huang Feng Liu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityShaanxi 710072China Northwest Institute for Nonferrous Metal Research Xi’an 710016China Analytical&Testing Center Northwestern Polytechnical UniversityShaanxi 710072China

***,Understanding and predicting microstructure and its relationship with the mechanical properties of metallic materials require detailed knowledge of phase transformations(PTs)and plastic deformations(PDs).These two processes,as central topics in material science,can be fundamentally described to a large extent by a framework of thermodynamic and kinetics(thermo-kinetics).The situation of PTs arises when the microstructure is losing phase stability,whereas the issue of PDs corresponds to the break of mechanical stability,all of which can be uniformly defined as the so-called loss of thermodynamic stability(TS).In this context,the higher TS will lead to the higher driving force G essentially required for the PT and/or PD forming and/or changing the *** the case of PTs,extensive examples showing the high TS can be found,such as martensite transformations(MTs)upon continuous cooling or strain[1,2],coherent precipitation[3,4],so-called Schwarz crystal[5],etc.

关键词： microstructure martensite stability

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Insights into plastic deformation mechanisms of austenitic steels by coupling generalized stacking fault energy and semi-discrete variational Peierls-Nabarro model

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Progress in Natural Science:Materials International 2023年第1期33卷 83-91页

作者： Yu Liu Jinglian Du Shunli Shang Ang Zhang Shoumei Xiong Zi-Kui Liu Feng Liu State Key Laboratory of Solidification Processing Northwestern Polytechnical University Department of Materials Science and Engineering The Pennsylvania State University University Park College of Materials Science and Engineering Chongqing University School of Materials Science and Engineering Tsinghua University Analytical & Testing Center Northwestern Polytechnical University

The generalized stacking fault energy（GSFE） is a key parameter to determine the plastic deformation mechanisms of austenitic steels. However, the underlying physics why the GSFE can affect the plastic deformation behaviors remains unclear. In this paper, the plastic deformation mechanisms of austenitic steels with different carbon（C）additions were investigated by coupling the GSFE with the semi-discrete variational Peierls-Nabarro（P–N） *** internal mechanisms behind the P–N stress and plastic deformation were explained at atomic scale. It is found that the positions and contents of C atoms affect the GSFE of austenite, and thus regulate plastic deformation behaviors of austenitic steels by influencing dislocation core structure. As exemplified that with 4 at.%C in austenite, the intrinsic stacking fault energy increases from-433 to-264 mJ/m2, and the stacking fault width increases to 6.62b from 4.72b of FCC-Fe with b being the Burgers vector. This corresponds to the plastic deformation mechanism dominated by the ε martensitic transformation with the lattice changing from FCC to *** increasing C contents to 8 at.%, the intrinsic stacking fault energy of austenite increases to-9.01 mJ/m2,while the stacking fault width decreases to 6.03b. The plastic deformation tends to proceed via the mechanical twinning mode. The present investigation establishes a solid foundation for clarifying the plastic deformation mechanisms of austenitic steels from the perspective of the dislocation core structure.

关键词： Austenite Plastic deformation mechanisms Dislocation core structure Generalized stacking fault energy Peierls-Nabarro model

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Generalized stability criterion for controlling solidification segregation upon twin-roll casting

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Journal of Materials Science & Technology 2023年第3期134卷 163-177页

作者： Pan Wu Yubing Zhang Jiaqi Hu Shaojie Song Yong Li Huiyuan Wang Guo Yuan Zhaodong Wang Shizhong Wei Feng Liu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Analytical and Testing Center Northwestern Polytechnical UniversityXi’an 710072China State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819China State Key Laboratory of Super hard Materials Jilin UniversityChangchun 130012China National Joint Engineering Research Center for Abrasion Control and Molding of Metal Materials Henan University of Science and TechnologyLuoyang 471003China

Macro-and micro-segregation formed upon twin-roll casting(TRC)can be inherited from sub-rapid solid-ification to solid-state transformation,even to plastic deformation,thus deteriorating drastically mechan-ical properties of as-produced thin *** many works focusing mainly on controlling fields of thermal,concentration and convection have been reported,how to control artificially and quantitatively the segregation using a theoretical connection between processing parameters and solidification models,has not been realized,*** it,a systematical framework integrating non-equilibrium dendritic growth and overall solidification kinetics with the TRC parameters,was constructed applying a general-ized stability(GS)conception deduced from transient thermodynamic driving force△G^(t)and transient ki-netic energy barrier Q_(eff)^(t)evolving upon *** from this framework considering synergy of thermodynamics and kinetics(i.e.,thermo-kinetic synergy),a criterion of high△G^(t)-high GS guaranteed that the macro(i.e.,the centerline)and the micro(i.e.,the edge)segregation can be suppressed by in-creasing△G^(t)and GS at the beginning and the ending stage of sub-rapid solidification,*** typical thermo-kinetic combination producing the microstructure can be inherited into the plastic de-formation,as reflected by corresponding strength-ductility *** work realized quantitative controlling of TRC by a theoretical connection between processing parameters and solidification models,where,an optimization for sub-rapid solidification segregation using the GS conception including△G^(t)and Q_(eff)^(t)has been performed.

关键词： Segregation Sub-rapid solidification Generalized stability Twin-roll casting Thermo-kinetics

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Indium oxide buffer layer for perovskite/Si 4-terminal tandem solar cells with efficiency exceeding 30%

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Journal of Energy Chemistry 2025年第3期102卷 189-196页

作者： Liming Du Can Li Yuhui Jiang Fangfang Cao Chunmei Jia Zhi Wan Rui Meng Jishan Shi Chuanxiao Xiao Zhe Liu Zhen Li State Key Laboratory of Solidification Processing Center for Nano Energy MaterialsSchool of Materials Science and EngineeringNorthwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene(NPU)Xi'an710072ShaanxiChina Ningbo Institute of Materials Technology and Engineering Chinese Academy of SciencesNingbo 315201ZhejiangChina Ningbo New Materials Testing and Evaluation Center Co. Ltd.Ningbo 315201ZhejiangChina

Perovskite/Si tandem solar cells(TSCs)present great potential to surpass the Shockley-Queisser limit of single-junction solar cells for further advancing the power conversion efficiency(PCE)of solar ***,the fabrication of TSCs usually encounters challenge of selecting suitable sputtering buffer layer(SBL)to prevent the bombardment during the transparent electrode ***,we introduce an indium oxide(In_(2)O_(3))buffer layer via e-beam deposition to fabricate semi-transparent perovskite solar cells(ST-PSCs).The optical transmittance and electrical conductivity of In_(2)O_(3)highly depend on the deposition *** deposition rate results in high ratio of metallic indium in the film,which causes severe parasitic absorption.A 20 nm-thick In_(2)O_(3)film deposited at lower rate demonstrated high conductivity,transmittance and robust protection during sputtering.A 1.68 eV ST-PSC incorporating this In_(2)O_(3)buffer layer exhibits a champion PCE of 20.20%,demonstrating the excellent optoelectronic and protective properties of In_(2)O_(3).When combined with a Si subcell,the 4-terminal TSC obtains a remarkable PCE of 30.04%,Importantly,the unencapsulated ST-PSC maintained 80%of initial PCE after 423 h of continuous light soaking in N_(2).This work has provided a facile and instrumental transparent SBL strategy for perovskite/Si TSCs.

关键词： E-beam deposition Sputtering Transparent electrode Perovskite solar cells In_(2)O_(3)

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Formation mechanism of partial stacking faults by incompletemixed-mode phase transformation: A case study of Fe-Ga alloys

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Journal of Materials Science & Technology 2022年第22期117卷 59-64页

作者： Tianzi Yang Tianyu Ma Feng Liu Xiaobing Ren Frontier Institute of Science and Technology State Key Laboratory for Mechanical Behavior of Materialsand MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed MatterXi’an Jiaotong UniversityXi’an 710049China State Key Laboratory of Solidification Processing and Analytical and Testing Center Northwestern Polytechnical UniversityXi’an 710072China Center for Functional Materials National Institute for Materials ScienceTsukuba 305-0047IbarakiJapan

Partial stacking faults(PSFs) formed by incomplete mixed-mode phase transformation have been found to exhibit unfixed slip distance of closely-packed planes unlike those of the deformation-induced stacking faults(SFs) with fixed distance. Though engineering PSFs can yield appealing properties, such as the enhanced damping capacity, understanding of the interaction between lattice distortion and atomic diffusion and their influences on forming PSFs is still far from being clear. Herein we performed a case study on aged Fe-Ga alloy that undergoes a mixed-mode phase transformation from body-centered cubic(BCC)to ordered face-centered cubic(FCC). The TEM investigations showed that the faulted {111}-FCC distance of the PSFs is shorter than a/6<112> of the typical {111}-<112> SFs in deformed FCC materials and the PSFs have disordered Fe and Ga arrangements. Further studies revealed that such PSFs will not be completely dissociated at FCC twin boundaries(TBs) even after long term isothermal aging. Consequently,the formation of PSFs can be ascribed to the transformation-dependent atomic ordering and lattice shear strain of the parent BCC lattice, where the diffusion-controlled glides of the PSFs-associated dislocations will accelerate atomic diffusions due to the dislocation-pipe effect along <112>-FCC direction, but may hinder the atomic diffusions across the {111}-FCC TBs due to the retarding effect. This study may add important insight into the defects process during mixed-mode phase transformation and broaden the knowledge of the interaction between concurrently-happened lattice distortion and atomic diffusion.

关键词： Stacking faults Mixed-mode phase transformation Diffusion Lattice distortion Fe-Ga alloy

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Improved mechanical properties of V-microalloyed dual phase steel by enhancing martensite deformability

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Journal of Materials Science & Technology 2021年第16期75卷 139-153页

作者： Jingbin Zhang Yinrui Sun Zhijie Ji Haiwen Luo Feng Liu State Key Laboratory of Solidification Processing Northwestern Poly technical UniversityXi'an 710072China Analytical&Testing Center Northwestern Polytechnical UniversityXi'an710072China University of Science and Technology Beijing Beijing 100081China

A good combination of ultimate tensile strength(UTS)up to 1365 MPa and total strain to failure(StF)to 15.5%has been achieved due to deformable martensite in the invented vanadium-microalloyed dual-phase(DP)steel,which was manufactured by two-stage annealing of cold rolled steel *** employed extensive characterizations revealed that the ductile martensitic phase in this DP steel differentiated from ordinarily low-carbon martensitic lath in both morphology and lattice *** coherent orientation relationships between ferrite,reverse austenite,martensitic phase and vanadium carbide(VC)do exist,leading to a new martensitic transformation mechanism and resultant dual-phase ***,a detailed characterization including essential phase transformation analysis in combination with in situ TEM observation,shows that,all the essential processing including recrystallization,reverse austenitic and martensitic transformation,in debt to the particular effects of VC,can be recognized as phase transformations with higher thermodynamic driving force and higher kinetic energy barrier as compared to previously common processing,which actually changes the microstructure and,indirectly leads to higher strength and higher *** synergy of thermodynamics and kinetics can be generalized to improve mechanical properties of present steels.

关键词： Dual-phase steel Deformability Martensitic phase Thermodynamics Kinetics

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