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Improved multi-order parameter and multi-component model of polycrystalline solidification

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Journal of Materials Science & Technology 2022年第6期101卷 217-225页

作者： Laishan Yang Zhibo Dong Lei Wang Nikolas Provatas State Key Laboratory of Advanced Welding and Joining Harbin Institute of TechnologyHarbin 150001China max-planck-institut für eisenforschung gmbh Max-Planck-Straße 1Düsseldorf40237Germany Department of Physics and Centre for the Physics of Materials McGill UniversityMontrealH3A 2T8Canada

In this paper, we present an improved multi-order parameter model for multi-component model of polycrystalline solidification. We introduce an interpolation function in the phase field dynamical equation to obtain controllable grain boundary energy at large undercooling. The same interpolation function is also employed in the kinetics coefficient to allow for better control of grain boundary migration. Temperature dependent phase field parameters and noise terms are consistently coupled into the dynamics of a binary system in a manner that allows for quantitative simulations in the thin interface limit. The model is applied to multi-phase solidification in Al-Cu alloy, where a parabolic fitting method is employed to model the free energy of Al-Cu phases and two-phase nucleation is demonstrated in directional solidification.

关键词： Phase field model Multi-phase Multi-component Grain boundary Consistent nucleation

In situ nanomechanical characterization of hydrogen effects on nickel-based alloy 725 under different metallurgical conditions

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Journal of Materials Science & Technology 2023年第4期135卷 156-169页

作者： Xu Lu Yan Ma Ding Peng Roy Johnsen Dong Wang Department of Mechanical and Industrial Engineering Norwegian University of Science and Technology(NTNU)7491 TrondheimNorway max-planck-institut für eisenforschung gmbh 40237 DüsseldorfGermany Department of Physics Norwegian University of Science and Technology(NTNU)7491 TrondheimNorway

The effect of hydrogen on the surface morphology and nanomechanical properties of Ni-based Alloy 725 under solution-annealed(SA)and precipitation-hardened(API)conditions was thoroughly studied.The investigation involved in situ nanoindentation testing,microscopy characterization,statistical analy-sis,and numerical simulation approaches.The results showed the distinctive effects of hydrogen on the pop-in and hardness in the SA and API samples.For the SA sample,hydrogen mainly dissolved as solid solute in the matrix,causing enhanced lattice friction on the dislocation motion and increasing the in-ternal stress via lattice expansion.Thus,an enhanced hardness,a reduced pop-in width/load ratio,and numerous surface steps were detected in the presence of hydrogen.For the API sample,the strengtheningγ″phases were the stress concentrators,and the dislocations nucleated heterogeneously,demonstrating indistinctive pop-in phenomena.Furthermore,the precipitates in the API sample affected the trapping be-havior of hydrogen,thereby resulting in the hardness change,which reflected the competition between solution hardening in the matrix and vacancy softening mechanism in precipitates.

关键词： Hydrogen Nickel-based alloy In situ nanoindentation Precipitates Dislocation nucleation Hardness

Kinetic modeling of high-temperature oxidation of pure Mg

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Journal of Magnesium and Alloys 2020年第3期8卷 819-831页

作者： Sa Ma Fangzhou Xing Na Ta Lijun Zhang State Key Laboratory of Powder Metallurgy Central South UniversityChangshaHunan 410083P.R.China max-planck-institut fiir eisenforschung gmbh Max-Planck-Straβe 140237DusseldorfGermany

A variety of experimental tracer diffusivities of Mg and O in magnesium oxide available in the literature were first assessed.Atomic mobilities including bulk and short-circuit diffusion of Mg and O were then obtained by means of the CALPHAD(Calculation of Phase Diagram)approach.Afterwards,the diffusion-controlled kinetic model of oxidation in a gas-MgO-Mg environment was developed based on the moving boundary model and Fick's law,coupling with the modified thermodynamic description of MgO.A mathematical expression for parabolic rate constant kp of the oxide scale was derived for magnesia and correlated with the thermodynamic and diffusion kinetic information.The evaluated kp results were in line with the experimental data.Finally,the oxidation process of pure magnesium at 673 K was model-predicted,and the predicted evolution of the oxide thicknesses agreed very well with the experimental data.It was indicated that the grain boundaries diffusion of magnesium cations predominated the high temperature oxidation process.

关键词： MgO Diffusion Oxidation Atomic mobility CALPHAD Wagner's model

A machine learning approach to model solute grain boundary segregation

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npj Computational Materials 2018年第1期4卷 130-137页

作者： Liam Huber Raheleh Hadian Blazej Grabowski Jörg Neugebauer max-planck-institut für eisenforschung gmbh D-40237 DüsseldorfGermany

Even minute amounts of one solute atom per one million bulk atoms may give rise to qualitative changes in the mechanical response and fracture resistance of modern structural materials.These changes are commonly related to enrichment by several orders of magnitude of the solutes at structural defects in the host lattice.The underlying concept—segregation—is thus fundamental in materials science.To include it in modern strategies of materials design,accurate and realistic computational modelling tools are necessary.However,the enormous number of defect configurations as well as sites solutes can occupy requires models which rely on severe approximations.In the present study we combine a high-throughput study containing more than 1 million data points with machine learning to derive a computationally highly efficient framework which opens the opportunity to model this important mechanism on a routine basis.

关键词： grain solute boundary

Effects of inter-layer remelting frequency on the microstructure evolution and mechanical properties of equimolar CoCrFeNiMn high entropy alloys during in-situ powder-bed arc additive manufacturing(PBAAM)process

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Journal of Materials Science & Technology 2022年第18期113卷 90-104页

作者： Jun Wang Yao Lu Fanghui Jia Wenzhen Xia Fei Lin Jian Han Ruichao Wang Zengxi Pan Huijun Li Zhengyi Jiang School of Mechanical Materials Mechatronic and Biomedical EngineeringUniversity of WollongongWollongongNew South Wales 2522Australia School of Metallurgical Engineering Anhui University of TechnologyMaanshan 243000China Department of Structure and Nano-/Micromechanics of Materials Max-Planck-Institut für Eisenforschung GmbHDüsseldorf 40237Germany Faculty of Intelligent Manufacturing Wuyi UniversityGuangdong 529020China

An equiatomic CoCrFeNiMn High Entropy Alloy(HEA)was in-situ deposited by the powder-bed arc ad-ditive manufacturing(PBAAM)process for the first time.Comparative research was conducted on the evolution of phase,crystallographic orientation,dislocation morphology,precipitation,and mechanical performance with the accumulation of inter-layer remelting times.The experimental outcomes mani-fested that the PBAAMed CoCrFeNiMn HEA consists of a stable solid-solution FCC structure,with de-creased lattice parameter but slightly increased(full width at half maximum)FWHM as the accumulation of the inter-layer remelting.The{001}cube texture with a weakened texture intensity was de-tected with an increment of inter-layer remelting frequency from once to 5 times,yet it was transformed into{011}Goss texture with a further increase to 7 times.Additionally,the mean grain diameter distinctly decreased,while the volume fraction of(low angle grain boundaries)LAGBs and dislocation density remarkably added up as the accumulated inter-layer remelts.Predominant cellular substructure generated in all process conditions and could be easily differentiated by elemental segregation.Both theσand M 23 C 6 Cr-rich precipitates in nano-scale and submicron MnS precipitate were detected on the grain boundaries of the PBAAMed deposited components,with a rather sparse distribution.Speaking of mechanical performance,the YS,UTS,and hardening rate are generally increased while the UE is grad-ually decreased as increased inter-layer remelting times.The studied PBAAMed CoCrFeNiMn HEA pos-sesses comparable mechanical performances with the counterparts of laser-deposited and as-cast ones.The strengthening mechanisms of the studied material are predominantly the grain boundary strength-ening and dislocation strengthening.This investigation would be a valuable resource in the research field of fabricating HEA alloys with acceptable microstructure and properties using the PBAAM method.

关键词： CoCrFeNiMn HEA Powder-bed arc additive manufacturing (PBAAM) Microstructure Phase Mechanical properties

Crystal plasticity model to predict fatigue crack nucleation based on the phase transformation theory

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Acta Mechanica Sinica 2019年第5期35卷 1033-1043页

作者： Lu Liu Jundong Wang Tao Zeng Yao Yao School of Mechanics Civil Engineering and ArchitectureNorthwestern PolytechnicalUniversityXi'an 710072China max-planck-institut für eisenforschung gmbh Max Planck Str.140237 DüsseldorfGermany

A crystal plasticity model is developed to predict the fatigue crack nucleation of polycrystalline materials,in which the accumulated dislocation dipoles are considered to be the origin of damage.To describe the overall softening behavior under cyclic loading,a slip system-level dislocation density-related damage model is proposed and implemented in the finite element analysis with Voronoi tessellation.The numerical model is applied to calibrate the stress-strain relationship at different cycles before fatigue crack nucleation.The parameters determined from the numerical analysis are substituted into a modified phase transformation model to predict the critical fatigue crack nucleation cycle.Comparing with the experimental results of Sn-3.0Ag-0.5Cu(SAC305)alloy and P91 steel,the proposed method can describe the constitutive behavior and predict the fatigue crack nucleation accurately.

关键词： Fatigue crack nucleation Damage Crystal plasticity Finite element Dislocation density

Magnetic Moment Tensor Potentials for collinear spin-polarized materials reproduce different magnetic states of bcc Fe

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npj Computational Materials 2022年第1期8卷 107-112页

作者： Ivan Novikov Blazej Grabowski Fritz Körmann Alexander Shapeev Skolkovo institute of Science and Technology Skolkovo Innovation CenterNobel St.3Moscow143026Russia institute for Materials Science University of StuttgartPfaffenwaldring 5570569StuttgartGermany Computational Materials Design Max-Planck-Institut für Eisenforschung GmbHD-40237DüsseldorfGermany Materials Science and Engineering Delft University of Technology2628 CDDelftThe Netherlands

We present the magnetic Moment Tensor Potentials(mMTPs),a class of machine-learning interatomic potentials,accurately reproducing both vibrational and magnetic degrees of freedom as provided,e.g.,from first-principles calculations.The accuracy is achieved by a two-step minimization scheme that coarse-grains the atomic and the spin space.The performance of the mMTPs is demonstrated for the prototype magnetic system bcc iron,with applications to phonon calculations for different magnetic states,and molecular-dynamics simulations with fluctuating magnetic moments.

关键词： magnetic fluctuating states

Thermal cycling creep properties of a directionally solidified superalloy DZ125

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Journal of Materials Science & Technology 2022年第9期104卷 269-284页

作者： Wenrui An Satoshi Utada Xiaotong Guo Stoichko Antonov Weiwei Zheng Jonathan Cormier Qiang Feng Beijing Advanced Innovation Center for Materials Genome Engineering State Key Laboratory for Advanced Metals and MaterialsUniversity of Science and Technology BeijingBeijing 100083China institut Pprime UPR CNRS 3346Department of Physics and Mechanics of MaterialsISAE-ENSMABP4010986961 Futuroscope Chasseneuil CedexFrance China Electronic Product Reliability and Environmental Testing Research institute Guangzhou 510610China Department of Microstructure Physics and Alloy Design Max-Planck-Institut für Eisenforschung GmbHDüsseldorf 40237Germany

Aero-engine turbine blades may suffer overheating during service,which can result in severe microstructural and mechanical degradation within tens of seconds.In this study,the thermal cycling creep under(950℃/15 min+1100℃/1 min)-100 MPa was performed on a directionally solidified superalloy,DZ125.The effects of overheating and thermal cycling on the creep properties were evaluated in terms of creep behavior and microstructural evolution against isothermally crept specimens under 950℃/100 MPa,950℃/270 MPa,and 1100℃/100 MPa.The results indicated that the thermal cycling creep life was reduced dramatically compared to the isothermal creep under 950℃/100 MPa.The plastic creep deformation mainly occurred during the overheating stage during the thermal cycling creep.The thermal cycling creep curve exhibited three stages,similar to the 1100℃isothermal creep,but its minimum creep rate occurred at a lower creep strain.The overheating events caused severe microstructural degradation,such as substantial dissolution ofγ'phase,earlier formation of raftedγ'microstructure,widening of theγchannels,and instability of the interfacial dislocation networks.This microstructural degradation was the main reason for the dramatic decrease in thermal cycling creep life,as the thermal cycling promoted more dislocations to cut intoγ'phase and more cracks to initiate at grain boundaries,carbides,and residual eutectic pools.This study underlines the importance of evaluating the thermal cycling creep properties of superalloys to be used as turbine blades and provides insights into the effect of thermal cycling on directionally solidified superalloys for component design.

关键词： Directional solidified superalloy Thermal cycling creep Overheating Creep properties Microstructural degradation

Convolutional neural network-assisted recognition of nanoscale L1_(2) ordered structures in face-centred cubic alloys

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npj Computational Materials 2021年第1期7卷 60-68页

作者： Yue Li Xuyang Zhou Timoteo Colnaghi Ye Wei Andreas Marek Hongxiang Li Stefan Bauer Markus Rampp Leigh T.Stephenson max-planck institut für eisenforschung gmbh Max-Planck-Straße 140237 DüsseldorfGermany max planck Computing and Data Facility Gießenbachstraße 285748 GarchingGermany State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing100083 BeijingChina max planck institute for Intelligent Systems Max-Planck-Ring 472076 TübingenGermany

Nanoscale L12-type ordered structures are widely used in face-centered cubic(FCC)alloys to exploit their hardening capacity and thereby improve mechanical properties.These fine-scale particles are typically fully coherent with matrix with the same atomic configuration disregarding chemical species,which makes them challenging to be characterized.Spatial distribution maps(SDMs)are used to probe local order by interrogating the three-dimensional(3D)distribution of atoms within reconstructed atom probe tomography(APT)data.However,it is almost impossible to manually analyze the complete point cloud(>10 million)in search for the partial crystallographic information retained within the data.Here,we proposed an intelligent L1_(2)-ordered structure recognition method based on convolutional neural networks(CNNs).The SDMs of a simulated L1_(2)-ordered structure and the FCC matrix were firstly generated.These simulated images combined with a small amount of experimental data were used to train a CNN-based L1_(2)-ordered structure recognition model.Finally,the approach was successfully applied to reveal the 3D distribution of L1_(2)–typeδ′–Al3(LiMg)nanoparticles with an average radius of 2.54 nm in a FCC Al-Li-Mg system.The minimum radius of detectable nanodomain is even down to 5Å.The proposed CNN-APT method is promising to be extended to recognize other nanoscale ordered structures and even more-challenging short-range ordered phenomena in the near future.

关键词： alloys ordered cubic