The evolution of ordered interphase boundary (IPB) of Ni75AlxV25-x alloys was simulated using the microscopic phase-field method. Based on the atomic occupation probability figure on 2D and order parameters, it was fo...The evolution of ordered interphase boundary (IPB) of Ni75AlxV25-x alloys was simulated using the microscopic phase-field method. Based on the atomic occupation probability figure on 2D and order parameters, it was found that the IPB formed by different directions ofθ phase has great effect on the precipitation of γ ′ phase. The γ ′ phase precipitated at the IPB that is formed by [1 00]θ direction where the ( 001)θ plane is opposite, and then grows up and the shape is strap at final. The IPB structure between γ ′phase andθ phase is the same. There is no γ ′ phase precipitate at the IPB where the ( 002)θ and ( 001)θ planes are opposite, the ordered IPB is dissolved into disordered area. There is γ ′ phase precipitation at the IPB formed by the [ 001]θ and [1 00]θ directions, and the IPB structure is different between γ ′ phase and the different directions ofθ phase. The IPB where ( 001)γ′ and (1 00)θ plane opposite does not migrate during the γ ′ phase growth, and γ ′ phase grows along [1 00]θdirection.展开更多
A microscopic phase-field model was used to investigate a directional coarsening mechanism caused by the anisotropic growth of long period stacking and different effects of phases on precipitation in Ni-Al-V alloy.The...A microscopic phase-field model was used to investigate a directional coarsening mechanism caused by the anisotropic growth of long period stacking and different effects of phases on precipitation in Ni-Al-V alloy.The results show that DO22 mainly coarsens along its short axis,which may press the neighboring L12,leading to the interaction among atoms.Diffusion channels of Al are formed in the direction where the mismatch between γ＇ and γ reduces;the occupation probabilities are anisotropic in space;and direction coarsening of L12 occurs finally.With a rise of ageing temperature,phases appear later and DO22 is much later at a higher temperature,the average occupation probabilities of Al and V reduce,and Al changes more than V.展开更多
The early precipitation process of Ni（75）Al（14）Mo（11） alloy was simulated by microscopic phase-field model at different temperatures.The microstructure of the alloy,the precipitation time of Llo structure and oc...The early precipitation process of Ni（75）Al（14）Mo（11） alloy was simulated by microscopic phase-field model at different temperatures.The microstructure of the alloy,the precipitation time of Llo structure and occupation probability of the three kinds of atoms were investigated.It is indicated that the non-stoichiometric Ll0（Ⅰ/Ⅱ） phases are found in the precipitation process.With the temperature increasing,the appearance time of Ll0 is brought forward.The Ll0（Ⅱ） structure always precipitates earlier than the Ll0（Ⅰ） structure.Compared with lower temperature,higher temperature brings the formation time of Ll0 phase forward and makes Ll0 phase have a higher order degree.But lower temperature shortens the process time of the Ll0 phase to the Ll2 phase.Al and Mo atoms tend to occupy γ site,Ni atom tends to occupy a and β sites.At the same temperature,Al atom has stronger occupation ability than Mo atom in the same site.Ni,Al and Mo collectively form the composited Ll2 structure.展开更多
Microscopic phase-field method was used to simulate the site occupation of a series of alloys with a stoichiometric composition of Ni75Al25?xFex (x=0, 5?10) aged at 1273 K. With the change of Fe content, quantitative ...Microscopic phase-field method was used to simulate the site occupation of a series of alloys with a stoichiometric composition of Ni75Al25?xFex (x=0, 5?10) aged at 1273 K. With the change of Fe content, quantitative calculations were made on each atomic site occupation probability (SOP) in L12-Ni3 (Al1?xFex), so as to find out the dynamic response law. The result of the study shows that, with the increase of Fe content, the Fe atom preferentially occupies the B sites (corner sites of FCC) with its SOP value being increased gradually, and the SOP of the Al atom on the B sites is greatly decreased. Meanwhile, AlNi and FeNi anti-sites form in the precipitation of L12 phase. Moreover, with the increase of Fe content, the formation of AlNi and FeNi anti-sites becomes much easier. In addition, it has been found that the instantaneous dynamic evolution of the atomic SOP is completed at the early stage of the growth of L12 phases.展开更多
Abstract The process of γ＇ phase precipitating from Ni75Al14MO11 is studied by a computational simulation technique based on microscopic phase-field kinetics model. We studied the phase transformation with the purpo...Abstract The process of γ＇ phase precipitating from Ni75Al14MO11 is studied by a computational simulation technique based on microscopic phase-field kinetics model. We studied the phase transformation with the purpose of clarifying the influence of the nearest interatomic potential V Ni-Al （the nearest interatomic potential） on the precipitation process of γ＇ phase. The result demonstrates that there are two kinds of ordered phases, respective Llo and L12 in the early stage, and Llo phase transforms into L12 phase subsequently. For L12 phase, Ni atoms mainly occupy α site （face center positions）, while Al and Mo atoms occupy fl sites （the vertex positions）. When VNi-Al is increased by 10 MeV, the occupation probability of Ni atoms on α sites and Al atoms on β sites are enhanced. Enhanced VNi-Al facilitates clustering and ordering of Al atom, which promotes the formation of the γ＇ phase. At last, the simulation result was discussed by employing the thermodynamic stability.展开更多
On the basis of the microscopic phase-field dynamic model and the microelasticity theory, the characteristics of the coarsening behavior of γ＇ phase in Ni-Al alloys have been systematically studied in a certain volu...On the basis of the microscopic phase-field dynamic model and the microelasticity theory, the characteristics of the coarsening behavior of γ＇ phase in Ni-Al alloys have been systematically studied in a certain volume fraction of the precipitates. It was found that the initial irregular shape, randomly distributed γ＇ phase, gradually transformed into cuboidal shape, regularly aligned along the [100] and [010] directions, and a highly preferential selected microstructure was formed during the later stage of precipitation. The volume fraction of the precipitates produced some effects on the precipitate morphology but did not produce an obvious effect on the regularities of precipitate distribution. The coarsening rate constant from the cubic growth law decreased as a function of volume fraction for small volume fractions, remained constant for intermediate volume fractions, and increased as a function of volume fraction for large volume fractions. During the coherent coarsening process, four ＂splitting＂ patterns between γ＇ phases, which belonged to different antiphase domains, were produced via particle aggregation, such as an L-shaped pattern, a doublet, a triplet, and a quartet.展开更多
With the microscopic phase-field dynamic model, the effects of temperature and concentration on the nucleation incubation time of Ni75AlxV25-x alloy were studied and the relation between the incubation time and precip...With the microscopic phase-field dynamic model, the effects of temperature and concentration on the nucleation incubation time of Ni75AlxV25-x alloy were studied and the relation between the incubation time and precipitation mechanism was investigated by using the atomic occupation probability picture and average order parameter curve. The simulation results demonstrate that there exists the incubation time for different precipitation mechanisms~ such as non-classical nucleation, the mixed style of non-classical nucleation and spinodal decomposition, and spinodal ordering; and the incubation time shortens in turn for the three kinds of mechanisms. With the increase of Al content of Ni75AlxV25-x alloy, the incubation time of Llz phases shortens continuously and that of DOzz phases is prolonged. The effects of temperature on the incubation time of Llz and DOzz phases are accordant, i.e. the incuba- tion time is greatly prolonged with the temperature rising.展开更多
This article, by means of the ternary microscopic phase-field model, investigates the effects of re-ageing temperature on the precipitation of Ni75Al10Cr15 alloy with the help of atomic pictures, order parameters, par...This article, by means of the ternary microscopic phase-field model, investigates the effects of re-ageing temperature on the precipitation of Ni75Al10Cr15 alloy with the help of atomic pictures, order parameters, particle density, averaged radii, and volume fractions. During pre-ageing at 873 K, DO22 phases first appear through spinodal decomposition mechanism, and then L12 phases begin to form on the DO22 phase-boundaries through non-classical nucleation mechanism. In either of them, ordering process is obviously faster than atom clustering. At the late stage of re-ageing at 923 K, the elastic strain energy seems to exert stronger effects on microstructure, and DO22 and L12 phases exhibit directional alignment along 〈100〉 direction to a certain extent. When the temperature increases to 1 023 K, the influence of elastic strain energy begins to weaken, and the precipitated phases become randomly distributed in the matrix. The volume fraction of DO22 phase decreases to zero, whereas that of L12 phase first increases and then decreases with the temperature rising from 923 K to 1 123 K. On the whole, the effects of elastic strain energy make the coarsening behavior of both phases deviate from the time-law predictions by LSW diffusion-controlled growth theory.展开更多
The effects of temperature on atomic anti-site behaviors in L12-Ni3(AlFe) phases were studied using microscopic phase-field dynamic model in precipitation progress of Ni75Al20Fe5 alloy.The results show that with the i...The effects of temperature on atomic anti-site behaviors in L12-Ni3(AlFe) phases were studied using microscopic phase-field dynamic model in precipitation progress of Ni75Al20Fe5 alloy.The results show that with the increase of temperature,the formation of NiAl and AlNi anti-sites is much easier in Ni3(AlFe),and Ni and Al anti-site atoms show clearly stronger temperature-dependent than Fe anti-site atoms.The evolution progress of anti-site atoms is completed at the initial growth stage of L12-Ni3(AlFe) phases.The site occupation probabilities of Ni atoms on the sublattice A(NiNi,face centers sites of FCC),and Al and Fe atoms on the sublattice B(AlAl and FeAl,corners sites of FCC) all present the degressive tendency with the temperature increasing.Fe atoms mainly prefer to occupy the Al sublattice at the whole temperature range.展开更多
The simulations of Cr atom substitution character during the formation of L12 and DO22 phases in Ni-Cr-Al alloy were performed at 873 K based on microscopic phase-field model. It is found that the substitution of Cr i...The simulations of Cr atom substitution character during the formation of L12 and DO22 phases in Ni-Cr-Al alloy were performed at 873 K based on microscopic phase-field model. It is found that the substitution of Cr is affected by Cr and Al contents and limits of occupation probabilities of Cr atom in L12 phase are present. The precipitate is single L12 phase when the component is less than the limit, Cr atoms substitute the Al sublattices in Ll2 phase, and both of atoms Al and Cr occupy the β-sites and complex phases Ni3（Al1-xCrx） are formed; Cr atoms enter Ni sites when Al and Cr contents exceed the limit, and substitute β-sites or both of α- and β-sites. The DO22 phase is formed at the boundary of Ll2 phase.展开更多
The influence of temperature on the precipitation mechanism and sequence of L 12 and D022 phases during the early precipitation process of a Ni-15.Sat%Cr-14at%Al alloy was simulated based on the microscopic phase-fiel...The influence of temperature on the precipitation mechanism and sequence of L 12 and D022 phases during the early precipitation process of a Ni-15.Sat%Cr-14at%Al alloy was simulated based on the microscopic phase-field model. In the range from 873 to 1373 K, the precipitation mechanism transformed from spinodal decomposition to non-classic nucleation and growth; the incubation period prolonged gradually with increasing temperature. The volume fraction of L12 phases increased and that of D022 phases decreased. D022 phases disappeared at 1373 K, and finally single-phase L12 phases were formed.展开更多
The precipitating kinetics of Ni75Al17Zn8 alloy was studied at both 873K and 973K by microscopic phase-field model.The calculation results show that the order-disorder transformation experiences the matrix→lowly-orde...The precipitating kinetics of Ni75Al17Zn8 alloy was studied at both 873K and 973K by microscopic phase-field model.The calculation results show that the order-disorder transformation experiences the matrix→lowly-ordered L10 phase→L12 phase at 973 K.And the nucleation of L12 particles belongs to the spinodal decomposition mechanism.As temperature increases,orderings of Al and Zn atoms are resisted,but coarsening of L12 particles is promoted.The value of coarsening kinetic exponents approaches to 1/2.In addition,the discussions about Ni-Al anti-site defect and Zn substitutions for Ni site and Al site exhibit that the higher the temperature,the more distinctive the Ni-Al anti-site defect,but the less the Zn substitution.展开更多
Anode-free lithium metal batteries are prone to capacity degradation and safety hazards due to the formation and growth of lithium dendrites.The interface between the current collector and deposited lithium plays a cr...Anode-free lithium metal batteries are prone to capacity degradation and safety hazards due to the formation and growth of lithium dendrites.The interface between the current collector and deposited lithium plays a critical role in preventing dendrite formation by regulating the thermodynamics and kinetics of lithium deposition.In this study,we develop a phase field model to investigate the influence of the current collector’s surface energy on lithium deposition morphology and its effect on the quality of the lithium metal film.It is demonstrated that a higher surface energy of the current collector promotes the growth of lithium metal along the surface of the current collector.Further,our simulation results show that a higher surface energy accelerates the formation of the lithium metal film while simultaneously reducing its surface roughness.By examining different contact angles and applied potentials,we construct a phase diagram of deposition morphology,illustrating that increased surface energy facilitates the dense and uniform deposition of lithium metal by preventing the formation of lithium filaments and voids.These findings provide new insights into the development and application of anode-free lithium metal batteries.展开更多
Accurate prediction of coal reservoir permeability is crucial for engineering applications,including coal mining,coalbed methane(CBM)extraction,and carbon storage in deep unmineable coal seams.Owing to the inherent he...Accurate prediction of coal reservoir permeability is crucial for engineering applications,including coal mining,coalbed methane(CBM)extraction,and carbon storage in deep unmineable coal seams.Owing to the inherent heterogeneity and complex internal structure of coal,a well-established method for predicting permeability based on microscopic fracture structures remains elusive.This paper presents a novel integrated approach that leverages the intrinsic relationship between microscopic fracture structure and permeability to construct a predictive model for coal permeability.The proposed framework encompasses data generation through the integration of three-dimensional(3D)digital core analysis and numerical simulations,followed by data-driven modeling via machine learning(ML)techniques.Key data-driven strategies,including feature selection and hyperparameter tuning,are employed to improve model performance.We propose and evaluate twelve data-driven models,including multilayer perceptron(MLP),random forest(RF),and hybrid methods.The results demonstrate that the ML model based on the RF algorithm achieves the highest accuracy and best generalization capability in predicting permeability.This method enables rapid estimation of coal permeability by inputting two-dimensional(2D)computed tomography images or parameters of the microscopic fracture structure,thereby providing an accurate and efficient means of permeability prediction.展开更多
Simulations are performed on temporal evolution of atom morphology and ordering parameters of Ni-14.5 Cr-16.5 Al alloy during early precipitation process at different temperatures based on microscopic phase-field theo...Simulations are performed on temporal evolution of atom morphology and ordering parameters of Ni-14.5 Cr-16.5 Al alloy during early precipitation process at different temperatures based on microscopic phase-field theory; the relationship between precipitation sequence and mechanism of L12 and D022 structure and precipitation temperature are illuminated. The nonstoichiometric ordered L12 phases appear first with congruent ordering＋spinodal decomposition mechanism which is then followed by precipitation of D022 phases at ordering domain boundaries of L12 phases by spinodal decomposition mechanism at 1073 K and 1223 K. The nonstoichiometric L12 phases transform to stoichiometric ordering phases gradually. The incubation period of L12 and D022 phases is shorter at 1073 K than that 1223 K, and growth speed is higher at 1073 K. At 1373 K, L12 and D022 phases appear simultaneously by non-classical nucleation and growth mechanism. After that the particles of D022 phases diminish and disappear gradually; L12 phases grow and single L12 phases are remained at last.展开更多
Based on the microscopic phase-field dynamic model and the microelasticity theory,the coarsening behavior of L12 and DO22 phases in Ni75CrxAl25-x alloy was simulated.The results show that the initial irregular shaped,...Based on the microscopic phase-field dynamic model and the microelasticity theory,the coarsening behavior of L12 and DO22 phases in Ni75CrxAl25-x alloy was simulated.The results show that the initial irregular shaped,randomly distributed L12 and DO22 phases are gradually transformed into cuboidal shape with round corner,regularly aligned along directions[100]and[001],and highly preferential selected microstructure is formed during the later stage of precipitation.The elastic field produced by the lattice mismatch between the coherent precipitates and the matrix has a strong influence on the coarsening kinetics,and there is no linear relationship between the cube of the average size of precipitates and the aging time,which does not agree with the results predicted by the classical Lifshitz-Slyozov-Wagner.The coarsening processes of L12 and DO22 phases are retarded in elastically constrained system.In the concurrent system of L12 and DO22 phases,there are two types of coarsening modes:the migration of antiphase domain boundaries and the interphase Ostwald ripening.展开更多
A mathematical model combined projection algorithm with phase-field method was applied. The adaptive finite element method was adopted to solve the model based on the non-uniform grid, and the behavior of dendritic gr...A mathematical model combined projection algorithm with phase-field method was applied. The adaptive finite element method was adopted to solve the model based on the non-uniform grid, and the behavior of dendritic growth was simulated from undercooled nickel melt under the forced flow. The simulation results show that the asymmetry behavior of the dendritic growth is caused by the forced flow. When the flow velocity is less than the critical value, the asymmetry of dendrite is little influenced by the forced flow. Once the flow velocity reaches or exceeds the critical value, the controlling factor of dendrite growth gradually changes from thermal diffusion to convection. With the increase of the flow velocity, the deflection angle towards upstream direction of the primary dendrite stem becomes larger. The effect of the dendrite growth on the flow field of the melt is apparent. With the increase of the dendrite size, the vortex is present in the downstream regions, and the vortex region is gradually enlarged. Dendrite tips appear to remelt. In addition, the adaptive finite element method can reduce CPU running time by one order of magnitude compared with uniform grid method, and the speed-up ratio is proportional to the size of computational domain.展开更多
The use of aeolian sand(AS)as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits.Owing to the lack of research on the mechanism of cement...The use of aeolian sand(AS)as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits.Owing to the lack of research on the mechanism of cemented AS backfill(CASB),the response surface method(RSM)was adopted in this study to analyze the influence of ordinary Portland cement(PO)content(x_(1)),fly ash(FA)-AS(FA-AS)ratio(x_(2)),and concentration(x_(3))on the mechanical and microscopic properties of the CASB.The hydration characteristics and internal pore structure of the backfill were assessed through thermogravimetric/derivative thermogravimetric analysis,mercury intrusion porosimetry,and scanning electron microscopy.The RSM results show that the influence of each factor and interaction term on the response values is extremely significant(except x_(1)x_(3),which had no obvious effect on the 28 d strength).The uniaxial compressive strength(UCS)increased with the PO content,FA-AS ratio,and concentration.The interaction effects of x_(1)x_(2),x_(1)x_(3),and x_(2)x_(3) on the UCS at 3,7,and 28 d were analyzed.In terms of the influence of interaction items,an improvement in one factor promoted the strengthening effect of another factor.The enhancement mechanism of the curing time,PO content,and FA-AS ratio on the backfill was reflected in the increase in hydration products and pore structure optimization.By contrast,the enhancement mechanism of the concentration was mainly the pore structure optimization.The UCS was positively correlated with weight loss and micropore content but negatively correlated with the total porosity.The R^(2) value of the fitting function of the strength and weight loss,micropore content,and total porosity exceeded 0.9,which improved the characterization of the enhancement mechanism of the UCS based on the thermogravimetric analysis and pore structure.This work obtained that the influence rules and mechanisms of the PO,FA-AS,concentration,and interaction terms on the mechanical properties of the CASB provided a certain theoretical and engineering guidance for CASB filling.展开更多
Flexoelectricity is a two-way coupling effect between the strain gradient and electric field that exists in all dielectrics,regardless of point group symmetry.However,the high-order derivatives of displacements involv...Flexoelectricity is a two-way coupling effect between the strain gradient and electric field that exists in all dielectrics,regardless of point group symmetry.However,the high-order derivatives of displacements involved in the strain gradient pose challenges in solving electromechanical coupling problems incorporating the flexoelectric effect.In this study,we formulate a phase-field model for ferroelectric materials considering the flexoelectric effect.A four-node quadrilateral element with 20 degrees of freedom is constructed without introducing high-order shape functions.The microstructure evolution of domains is described by an independent order parameter,namely the spontaneous polarization governed by the time-dependent Ginzburg–Landau theory.The model is developed based on a thermodynamic framework,in which a set of microforces is introduced to construct the constitutive relation and evolution equation.For the flexoelectric part of electric enthalpy,the strain gradient is determined by interpolating the mechanical strain at the node via the values of Gaussian integration points in the isoparametric space.The model is shown to be capable of reproducing the classic analytical solution of dielectric materials incorporating the flexoelectric contribution.The model is verified by duplicating some typical phenomena in flexoelectricity in cylindrical tubes and truncated pyramids.A comparison is made between the polarization distribution in dielectrics and ferroelectrics.The model can reproduce the solution to the boundary value problem of the cylindrical flexoelectric tube,and demonstrate domain twisting at domain walls in ferroelectrics considering the flexoelectric effect.展开更多
It is important to calibrate micro-parameters for applying partied flow code(PFC)to study mechanical characteristics and failure mechanism of rock materials.Uniform design method is firstly adopted to determine the mi...It is important to calibrate micro-parameters for applying partied flow code(PFC)to study mechanical characteristics and failure mechanism of rock materials.Uniform design method is firstly adopted to determine the microscopic parameters of parallel-bonded particle model for three-dimensional discrete element particle flow code(PFC3D).Variation ranges of microscopic of the microscopic parameters are created by analyzing the effects of microscopic parameters on macroscopic parameters(elastic modulus E,Poisson ratio v,uniaxial compressive strengthσc,and ratio of crack initial stress to uniaxial compressive strengthσci/σc)in order to obtain the actual uniform design talbe.The calculation equations of the microscopic and macroscopic parameters of rock materials can be established by the actual uniform design table and the regression analysis and thus the PFC3D microscopic parameters can be quantitatively determined.The PFC3D simulated results of the intact and pre-cracked rock specimens under uniaxial and triaxial compressions(including the macroscopic mechanical parameters,stress−strain curves and failure process)are in good agreement with experimental results,which can prove the validity of the calculation equations of microscopic and macroscopic parameters.展开更多
基金Project (50071046) supported by the National Natural Science Foundation of China Project (2002AA331051)supported by the National Hi-Tech Research and Development Program of China
文摘The evolution of ordered interphase boundary (IPB) of Ni75AlxV25-x alloys was simulated using the microscopic phase-field method. Based on the atomic occupation probability figure on 2D and order parameters, it was found that the IPB formed by different directions ofθ phase has great effect on the precipitation of γ ′ phase. The γ ′ phase precipitated at the IPB that is formed by [1 00]θ direction where the ( 001)θ plane is opposite, and then grows up and the shape is strap at final. The IPB structure between γ ′phase andθ phase is the same. There is no γ ′ phase precipitate at the IPB where the ( 002)θ and ( 001)θ planes are opposite, the ordered IPB is dissolved into disordered area. There is γ ′ phase precipitation at the IPB formed by the [ 001]θ and [1 00]θ directions, and the IPB structure is different between γ ′ phase and the different directions ofθ phase. The IPB where ( 001)γ′ and (1 00)θ plane opposite does not migrate during the γ ′ phase growth, and γ ′ phase grows along [1 00]θdirection.
基金Projects(51075335,10902086,50875217) supported by the National Natural Science Foundation of ChinaProject(JC201005) supported by the Northwestern Polytechnical University Foundation for Fundamental Research,ChinaProject(CX201007) supported by the Doctorate Foundation of Northwestern Polytechnical University,China
文摘A microscopic phase-field model was used to investigate a directional coarsening mechanism caused by the anisotropic growth of long period stacking and different effects of phases on precipitation in Ni-Al-V alloy.The results show that DO22 mainly coarsens along its short axis,which may press the neighboring L12,leading to the interaction among atoms.Diffusion channels of Al are formed in the direction where the mismatch between γ＇ and γ reduces;the occupation probabilities are anisotropic in space;and direction coarsening of L12 occurs finally.With a rise of ageing temperature,phases appear later and DO22 is much later at a higher temperature,the average occupation probabilities of Al and V reduce,and Al changes more than V.
基金Project(51275486)supported by the National Natural Science Foundation of China
文摘The early precipitation process of Ni（75）Al（14）Mo（11） alloy was simulated by microscopic phase-field model at different temperatures.The microstructure of the alloy,the precipitation time of Llo structure and occupation probability of the three kinds of atoms were investigated.It is indicated that the non-stoichiometric Ll0（Ⅰ/Ⅱ） phases are found in the precipitation process.With the temperature increasing,the appearance time of Ll0 is brought forward.The Ll0（Ⅱ） structure always precipitates earlier than the Ll0（Ⅰ） structure.Compared with lower temperature,higher temperature brings the formation time of Ll0 phase forward and makes Ll0 phase have a higher order degree.But lower temperature shortens the process time of the Ll0 phase to the Ll2 phase.Al and Mo atoms tend to occupy γ site,Ni atom tends to occupy a and β sites.At the same temperature,Al atom has stronger occupation ability than Mo atom in the same site.Ni,Al and Mo collectively form the composited Ll2 structure.
基金Project(2013011014-1)supported by the Natural Science Funds of Shanxi Province,ChinaProject(2009021028)supported by Science and Technique Foundation for Young Scholars of Shanxi Province,China
文摘Microscopic phase-field method was used to simulate the site occupation of a series of alloys with a stoichiometric composition of Ni75Al25?xFex (x=0, 5?10) aged at 1273 K. With the change of Fe content, quantitative calculations were made on each atomic site occupation probability (SOP) in L12-Ni3 (Al1?xFex), so as to find out the dynamic response law. The result of the study shows that, with the increase of Fe content, the Fe atom preferentially occupies the B sites (corner sites of FCC) with its SOP value being increased gradually, and the SOP of the Al atom on the B sites is greatly decreased. Meanwhile, AlNi and FeNi anti-sites form in the precipitation of L12 phase. Moreover, with the increase of Fe content, the formation of AlNi and FeNi anti-sites becomes much easier. In addition, it has been found that the instantaneous dynamic evolution of the atomic SOP is completed at the early stage of the growth of L12 phases.
基金financially supported by the National Natural Science Foundation of China (Nos. 51,204,147 and 51274175)International Cooperation Project Supported by Ministry of Science and Technology of China (No. 2014DFA50320)International Science and Technology Cooperation Project of Shanxi Province (Nos. 2013081017 and 2012081013)
文摘Abstract The process of γ＇ phase precipitating from Ni75Al14MO11 is studied by a computational simulation technique based on microscopic phase-field kinetics model. We studied the phase transformation with the purpose of clarifying the influence of the nearest interatomic potential V Ni-Al （the nearest interatomic potential） on the precipitation process of γ＇ phase. The result demonstrates that there are two kinds of ordered phases, respective Llo and L12 in the early stage, and Llo phase transforms into L12 phase subsequently. For L12 phase, Ni atoms mainly occupy α site （face center positions）, while Al and Mo atoms occupy fl sites （the vertex positions）. When VNi-Al is increased by 10 MeV, the occupation probability of Ni atoms on α sites and Al atoms on β sites are enhanced. Enhanced VNi-Al facilitates clustering and ordering of Al atom, which promotes the formation of the γ＇ phase. At last, the simulation result was discussed by employing the thermodynamic stability.
基金This work was financially supported by the National Natural Science Foundation of China (No.50671084)China Postdoctoral Science Foundation (No.20070420218).
文摘On the basis of the microscopic phase-field dynamic model and the microelasticity theory, the characteristics of the coarsening behavior of γ＇ phase in Ni-Al alloys have been systematically studied in a certain volume fraction of the precipitates. It was found that the initial irregular shape, randomly distributed γ＇ phase, gradually transformed into cuboidal shape, regularly aligned along the [100] and [010] directions, and a highly preferential selected microstructure was formed during the later stage of precipitation. The volume fraction of the precipitates produced some effects on the precipitate morphology but did not produce an obvious effect on the regularities of precipitate distribution. The coarsening rate constant from the cubic growth law decreased as a function of volume fraction for small volume fractions, remained constant for intermediate volume fractions, and increased as a function of volume fraction for large volume fractions. During the coherent coarsening process, four ＂splitting＂ patterns between γ＇ phases, which belonged to different antiphase domains, were produced via particle aggregation, such as an L-shaped pattern, a doublet, a triplet, and a quartet.
文摘With the microscopic phase-field dynamic model, the effects of temperature and concentration on the nucleation incubation time of Ni75AlxV25-x alloy were studied and the relation between the incubation time and precipitation mechanism was investigated by using the atomic occupation probability picture and average order parameter curve. The simulation results demonstrate that there exists the incubation time for different precipitation mechanisms~ such as non-classical nucleation, the mixed style of non-classical nucleation and spinodal decomposition, and spinodal ordering; and the incubation time shortens in turn for the three kinds of mechanisms. With the increase of Al content of Ni75AlxV25-x alloy, the incubation time of Llz phases shortens continuously and that of DOzz phases is prolonged. The effects of temperature on the incubation time of Llz and DOzz phases are accordant, i.e. the incuba- tion time is greatly prolonged with the temperature rising.
基金Foundation items： National Natural Science Foundation of China （50671084） China Postdoctoral Science Foundation Funded Project （20070420218）
文摘This article, by means of the ternary microscopic phase-field model, investigates the effects of re-ageing temperature on the precipitation of Ni75Al10Cr15 alloy with the help of atomic pictures, order parameters, particle density, averaged radii, and volume fractions. During pre-ageing at 873 K, DO22 phases first appear through spinodal decomposition mechanism, and then L12 phases begin to form on the DO22 phase-boundaries through non-classical nucleation mechanism. In either of them, ordering process is obviously faster than atom clustering. At the late stage of re-ageing at 923 K, the elastic strain energy seems to exert stronger effects on microstructure, and DO22 and L12 phases exhibit directional alignment along 〈100〉 direction to a certain extent. When the temperature increases to 1 023 K, the influence of elastic strain energy begins to weaken, and the precipitated phases become randomly distributed in the matrix. The volume fraction of DO22 phase decreases to zero, whereas that of L12 phase first increases and then decreases with the temperature rising from 923 K to 1 123 K. On the whole, the effects of elastic strain energy make the coarsening behavior of both phases deviate from the time-law predictions by LSW diffusion-controlled growth theory.
基金Project(50671084) supported by the National Natural Science Foundation of ChinaProject(2009021028) supported by Science and Technique Foundation for Young Scholars of Shanxi Province, ChinaProject(20100470125) supported by National Science Foundation for Post-doctoral Scientists of China
文摘The effects of temperature on atomic anti-site behaviors in L12-Ni3(AlFe) phases were studied using microscopic phase-field dynamic model in precipitation progress of Ni75Al20Fe5 alloy.The results show that with the increase of temperature,the formation of NiAl and AlNi anti-sites is much easier in Ni3(AlFe),and Ni and Al anti-site atoms show clearly stronger temperature-dependent than Fe anti-site atoms.The evolution progress of anti-site atoms is completed at the initial growth stage of L12-Ni3(AlFe) phases.The site occupation probabilities of Ni atoms on the sublattice A(NiNi,face centers sites of FCC),and Al and Fe atoms on the sublattice B(AlAl and FeAl,corners sites of FCC) all present the degressive tendency with the temperature increasing.Fe atoms mainly prefer to occupy the Al sublattice at the whole temperature range.
基金Project(50071046) supported by the National Natural Science Foundation of China
文摘The simulations of Cr atom substitution character during the formation of L12 and DO22 phases in Ni-Cr-Al alloy were performed at 873 K based on microscopic phase-field model. It is found that the substitution of Cr is affected by Cr and Al contents and limits of occupation probabilities of Cr atom in L12 phase are present. The precipitate is single L12 phase when the component is less than the limit, Cr atoms substitute the Al sublattices in Ll2 phase, and both of atoms Al and Cr occupy the β-sites and complex phases Ni3（Al1-xCrx） are formed; Cr atoms enter Ni sites when Al and Cr contents exceed the limit, and substitute β-sites or both of α- and β-sites. The DO22 phase is formed at the boundary of Ll2 phase.
基金This work was financially supported by the National Natural Science Foundation of China (No.50071046) and the National High-Tech Research and Development Program of China (No.2002AA331051).
文摘The influence of temperature on the precipitation mechanism and sequence of L 12 and D022 phases during the early precipitation process of a Ni-15.Sat%Cr-14at%Al alloy was simulated based on the microscopic phase-field model. In the range from 873 to 1373 K, the precipitation mechanism transformed from spinodal decomposition to non-classic nucleation and growth; the incubation period prolonged gradually with increasing temperature. The volume fraction of L12 phases increased and that of D022 phases decreased. D022 phases disappeared at 1373 K, and finally single-phase L12 phases were formed.
基金Projects(50941020,10902086)supported by the National Natural Science Foundation of China
文摘The precipitating kinetics of Ni75Al17Zn8 alloy was studied at both 873K and 973K by microscopic phase-field model.The calculation results show that the order-disorder transformation experiences the matrix→lowly-ordered L10 phase→L12 phase at 973 K.And the nucleation of L12 particles belongs to the spinodal decomposition mechanism.As temperature increases,orderings of Al and Zn atoms are resisted,but coarsening of L12 particles is promoted.The value of coarsening kinetic exponents approaches to 1/2.In addition,the discussions about Ni-Al anti-site defect and Zn substitutions for Ni site and Al site exhibit that the higher the temperature,the more distinctive the Ni-Al anti-site defect,but the less the Zn substitution.
基金supported by the National Key Research and Development Program of China(2022YFA1203602)the National Natural Science Foundation of China(Grant No.12025206)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0620101)the National Natural Science Foundations of China(Grant No.12202366).
文摘Anode-free lithium metal batteries are prone to capacity degradation and safety hazards due to the formation and growth of lithium dendrites.The interface between the current collector and deposited lithium plays a critical role in preventing dendrite formation by regulating the thermodynamics and kinetics of lithium deposition.In this study,we develop a phase field model to investigate the influence of the current collector’s surface energy on lithium deposition morphology and its effect on the quality of the lithium metal film.It is demonstrated that a higher surface energy of the current collector promotes the growth of lithium metal along the surface of the current collector.Further,our simulation results show that a higher surface energy accelerates the formation of the lithium metal film while simultaneously reducing its surface roughness.By examining different contact angles and applied potentials,we construct a phase diagram of deposition morphology,illustrating that increased surface energy facilitates the dense and uniform deposition of lithium metal by preventing the formation of lithium filaments and voids.These findings provide new insights into the development and application of anode-free lithium metal batteries.
基金supported by the Zhejiang Provincial Natural Science Foundation of China(Grant No.LY23E040001)Fundamental Research Funding Project of Zhejiang Province,China(Project Category A,Grant No.2022YW06)National Key R&D Program of China(Grant No.2023YFF0614902).
文摘Accurate prediction of coal reservoir permeability is crucial for engineering applications,including coal mining,coalbed methane(CBM)extraction,and carbon storage in deep unmineable coal seams.Owing to the inherent heterogeneity and complex internal structure of coal,a well-established method for predicting permeability based on microscopic fracture structures remains elusive.This paper presents a novel integrated approach that leverages the intrinsic relationship between microscopic fracture structure and permeability to construct a predictive model for coal permeability.The proposed framework encompasses data generation through the integration of three-dimensional(3D)digital core analysis and numerical simulations,followed by data-driven modeling via machine learning(ML)techniques.Key data-driven strategies,including feature selection and hyperparameter tuning,are employed to improve model performance.We propose and evaluate twelve data-driven models,including multilayer perceptron(MLP),random forest(RF),and hybrid methods.The results demonstrate that the ML model based on the RF algorithm achieves the highest accuracy and best generalization capability in predicting permeability.This method enables rapid estimation of coal permeability by inputting two-dimensional(2D)computed tomography images or parameters of the microscopic fracture structure,thereby providing an accurate and efficient means of permeability prediction.
基金This work was supported by the National Natural Science Foundation of China （Grant No. 50071046） the National High-Tech Research and Development Program of China （863 Program, No. 2002AA331051）.
文摘Simulations are performed on temporal evolution of atom morphology and ordering parameters of Ni-14.5 Cr-16.5 Al alloy during early precipitation process at different temperatures based on microscopic phase-field theory; the relationship between precipitation sequence and mechanism of L12 and D022 structure and precipitation temperature are illuminated. The nonstoichiometric ordered L12 phases appear first with congruent ordering＋spinodal decomposition mechanism which is then followed by precipitation of D022 phases at ordering domain boundaries of L12 phases by spinodal decomposition mechanism at 1073 K and 1223 K. The nonstoichiometric L12 phases transform to stoichiometric ordering phases gradually. The incubation period of L12 and D022 phases is shorter at 1073 K than that 1223 K, and growth speed is higher at 1073 K. At 1373 K, L12 and D022 phases appear simultaneously by non-classical nucleation and growth mechanism. After that the particles of D022 phases diminish and disappear gradually; L12 phases grow and single L12 phases are remained at last.
基金Project(50671084)supported by the National Natural Science Foundation of ChinaProject(20070420218)supported by ChinaPostdoctoral Science Foundation
文摘Based on the microscopic phase-field dynamic model and the microelasticity theory,the coarsening behavior of L12 and DO22 phases in Ni75CrxAl25-x alloy was simulated.The results show that the initial irregular shaped,randomly distributed L12 and DO22 phases are gradually transformed into cuboidal shape with round corner,regularly aligned along directions[100]and[001],and highly preferential selected microstructure is formed during the later stage of precipitation.The elastic field produced by the lattice mismatch between the coherent precipitates and the matrix has a strong influence on the coarsening kinetics,and there is no linear relationship between the cube of the average size of precipitates and the aging time,which does not agree with the results predicted by the classical Lifshitz-Slyozov-Wagner.The coarsening processes of L12 and DO22 phases are retarded in elastically constrained system.In the concurrent system of L12 and DO22 phases,there are two types of coarsening modes:the migration of antiphase domain boundaries and the interphase Ostwald ripening.
基金Projects(51161011,11364024)supported by the National Natural Science Foundation of ChinaProject(1204GKCA065)supported by the Key Technology R&D Program of Gansu Province,China+1 种基金Project(201210)supported by the Fundamental Research Funds for the Universities of Gansu Province,ChinaProject(J201304)supported by the Funds for Distinguished Young Scientists of Lanzhou University of Technology,China
文摘A mathematical model combined projection algorithm with phase-field method was applied. The adaptive finite element method was adopted to solve the model based on the non-uniform grid, and the behavior of dendritic growth was simulated from undercooled nickel melt under the forced flow. The simulation results show that the asymmetry behavior of the dendritic growth is caused by the forced flow. When the flow velocity is less than the critical value, the asymmetry of dendrite is little influenced by the forced flow. Once the flow velocity reaches or exceeds the critical value, the controlling factor of dendrite growth gradually changes from thermal diffusion to convection. With the increase of the flow velocity, the deflection angle towards upstream direction of the primary dendrite stem becomes larger. The effect of the dendrite growth on the flow field of the melt is apparent. With the increase of the dendrite size, the vortex is present in the downstream regions, and the vortex region is gradually enlarged. Dendrite tips appear to remelt. In addition, the adaptive finite element method can reduce CPU running time by one order of magnitude compared with uniform grid method, and the speed-up ratio is proportional to the size of computational domain.
基金financially supported by the National Natural Science Foundation of China (NO.52174095)。
文摘The use of aeolian sand(AS)as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits.Owing to the lack of research on the mechanism of cemented AS backfill(CASB),the response surface method(RSM)was adopted in this study to analyze the influence of ordinary Portland cement(PO)content(x_(1)),fly ash(FA)-AS(FA-AS)ratio(x_(2)),and concentration(x_(3))on the mechanical and microscopic properties of the CASB.The hydration characteristics and internal pore structure of the backfill were assessed through thermogravimetric/derivative thermogravimetric analysis,mercury intrusion porosimetry,and scanning electron microscopy.The RSM results show that the influence of each factor and interaction term on the response values is extremely significant(except x_(1)x_(3),which had no obvious effect on the 28 d strength).The uniaxial compressive strength(UCS)increased with the PO content,FA-AS ratio,and concentration.The interaction effects of x_(1)x_(2),x_(1)x_(3),and x_(2)x_(3) on the UCS at 3,7,and 28 d were analyzed.In terms of the influence of interaction items,an improvement in one factor promoted the strengthening effect of another factor.The enhancement mechanism of the curing time,PO content,and FA-AS ratio on the backfill was reflected in the increase in hydration products and pore structure optimization.By contrast,the enhancement mechanism of the concentration was mainly the pore structure optimization.The UCS was positively correlated with weight loss and micropore content but negatively correlated with the total porosity.The R^(2) value of the fitting function of the strength and weight loss,micropore content,and total porosity exceeded 0.9,which improved the characterization of the enhancement mechanism of the UCS based on the thermogravimetric analysis and pore structure.This work obtained that the influence rules and mechanisms of the PO,FA-AS,concentration,and interaction terms on the mechanical properties of the CASB provided a certain theoretical and engineering guidance for CASB filling.
基金funded by the National Natural Science Foundation of China(Grant No.12272020)Beijing Natural Science Foundation(Grant No.JQ21001)+1 种基金S.W.acknowledges support from the Fundamental Research Funds for the Central Universities(Grant No.YWF-23-SDHK-L-019)M.Y.acknowledges support from the National Natural Science Foundation of China(Grant Nos.12302134,12272173,and 11902150).
文摘Flexoelectricity is a two-way coupling effect between the strain gradient and electric field that exists in all dielectrics,regardless of point group symmetry.However,the high-order derivatives of displacements involved in the strain gradient pose challenges in solving electromechanical coupling problems incorporating the flexoelectric effect.In this study,we formulate a phase-field model for ferroelectric materials considering the flexoelectric effect.A four-node quadrilateral element with 20 degrees of freedom is constructed without introducing high-order shape functions.The microstructure evolution of domains is described by an independent order parameter,namely the spontaneous polarization governed by the time-dependent Ginzburg–Landau theory.The model is developed based on a thermodynamic framework,in which a set of microforces is introduced to construct the constitutive relation and evolution equation.For the flexoelectric part of electric enthalpy,the strain gradient is determined by interpolating the mechanical strain at the node via the values of Gaussian integration points in the isoparametric space.The model is shown to be capable of reproducing the classic analytical solution of dielectric materials incorporating the flexoelectric contribution.The model is verified by duplicating some typical phenomena in flexoelectricity in cylindrical tubes and truncated pyramids.A comparison is made between the polarization distribution in dielectrics and ferroelectrics.The model can reproduce the solution to the boundary value problem of the cylindrical flexoelectric tube,and demonstrate domain twisting at domain walls in ferroelectrics considering the flexoelectric effect.
基金Projects(51474251,51874351)supported by the National Natural Science Foundation,China。
文摘It is important to calibrate micro-parameters for applying partied flow code(PFC)to study mechanical characteristics and failure mechanism of rock materials.Uniform design method is firstly adopted to determine the microscopic parameters of parallel-bonded particle model for three-dimensional discrete element particle flow code(PFC3D).Variation ranges of microscopic of the microscopic parameters are created by analyzing the effects of microscopic parameters on macroscopic parameters(elastic modulus E,Poisson ratio v,uniaxial compressive strengthσc,and ratio of crack initial stress to uniaxial compressive strengthσci/σc)in order to obtain the actual uniform design talbe.The calculation equations of the microscopic and macroscopic parameters of rock materials can be established by the actual uniform design table and the regression analysis and thus the PFC3D microscopic parameters can be quantitatively determined.The PFC3D simulated results of the intact and pre-cracked rock specimens under uniaxial and triaxial compressions(including the macroscopic mechanical parameters,stress−strain curves and failure process)are in good agreement with experimental results,which can prove the validity of the calculation equations of microscopic and macroscopic parameters.
