Simulation of pre-precipitation in Ni_(75)Al_(14)Mo_(11) alloy by microscopic phase-field model

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.

Microscopic phase-field modeling of atomic anti-site behaviors in precipitation progress of Ni_3(AlFe)

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.

Microscopic phase-field study on directional coarsening mechanism caused by interaction between precipitates in Ni-Al-V alloy

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.

Microscopic Calculation of Parameters of the sdg Interacting Boson Model for ^(104-110)Pd Isotopes

The parameters of the sdg interacting boson model Hamiltonian are calculated for the 104-110Pdisotopes.The calculations utilize the microscopic procedure based on the Dyson boson mapping proposedby Yang-Liu-Qi and extended to include the g boson effects.The calculated parameters reproduce thosevalues from the phenomenological fits.The resulting spectra are compared with the experimental spectra.

Impact Analysis of Microscopic Defect Types on the Macroscopic Crack Propagation in Sintered Silver Nanoparticles

Sintered silver nanoparticles(AgNPs)arewidely used in high-power electronics due to their exceptional properties.However,the material reliability is significantly affected by various microscopic defects.In this work,the three primary micro-defect types at potential stress concentrations in sintered AgNPs are identified,categorized,and quantified.Molecular dynamics(MD)simulations are employed to observe the failure evolution of different microscopic defects.The dominant mechanisms responsible for this evolution are dislocation nucleation and dislocation motion.At the same time,this paper clarifies the quantitative relationship between the tensile strain amount and the failure mechanism transitions of the three defect types by defining key strain points.The impact of defect types on the failure process is also discussed.Furthermore,traction-separation curves extracted from microscopic defect evolutions serve as a bridge to connect the macro-scale model.The validity of the crack propagation model is confirmed through tensile tests.Finally,we thoroughly analyze how micro-defect types influence macro-crack propagation and attempt to find supporting evidence from the MD model.Our findings provide a multi-perspective reference for the reliability analysis of sintered AgNPs.

Quantitative calculation on atomic site occupation during precipitation of Ni_3(Al_(1-x)Fe_x) by microscopic phase-field study

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.

Microscopic Determination of Leading Terms of the Interaction Hamiltonian Between sd- and g-Parts in the sdg IBM

Starting from one of the microscopic sdg interacting boson approximations, the lead-ing terms in the interaction Hamiltonian are discussed by using numerical investigations. Com-parisons of both the calculated levels and the overlap of wave functions between the exact re-sults and the approximations are made to find out negligible part in the Hamiltonian. The re-sults show that the leading terms given in this paper may provide a way to simplify the complexcalculations.

Microscopic phase-field simulation of the coarsening behavior of coherent precipitates in Ni-Al alloys

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.

Microscopic Phase-field Simulation of Competition Mechanism Between Ll_2 and D0_(22) Structure in Ni-Cr-Al Alloy

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.

Microscopic phase-field simulation of L1_2 and D0_(22) phases during the early precipitation process of Ni-Cr-Al alloys

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.

Microscopic phase-field simulation for nucleation incubation time of Ni_(75)Al_xV_(25-x)alloy

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.

Free dendritic growth model based on nonisothermal interface and microscopic solvability theory

Considering both the effect of nonisothermal nature of the solid/liquid interface and the microscopic solvability theory (MicST), a further improved version of free dendritic growth model for pure materials was proposed. Model comparison indicates that there is a higher temperature at the tip of dendrite predicted by the present model compared with the corresponding model with the isothermal solid/liquid interface assumption. This is attributed to the sidewise thermal diffusion, i.e. the gradient of temperature along the nonisothermal interface. Furthermore, it is indicated that the distinction between the stability criteria from MicST and marginal stability theory (MarST) is more significant with the increase of bath undercoolings. Model test also indicates that the present model can give an agreement with the available experimental data. It is finally concluded that the nonisothermal nature of the solid/liquid interface and the stability criterion from MicST should be taken into account in modeling free dendritic growth.

Microscopic phase-field simulation of Cr atom substitution character during formation of L1_2 and DO_22 phases in Ni-Cr-Al alloy

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.

Microscopic phase-field simulation for coarsening behavior of Ll_2 and DO_(22)phases of Ni_(75)Cr_xAl_(25-x) alloy

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.

Numerical Simulation of Two-Dimensional Dendritic Growth Using Phase-Field Model

In this article, we study the phase-field model of solidification for numerical simulation of dendritic crystal growth that occurs during the casting of metals and alloys. Phase-field model of solidification describes the physics of dendritic growth in any material during the process of under cooling. The numerical procedure in this work is based on finite difference scheme for space and the 4th-order Runge-Kutta method for time discretization. The effect of each physical parameter on the shape and growth of dendritic crystal is studied and visualized in detail.

Fourth-order phase-field modeling for brittle fracture in piezoelectric materials

Failure analyses of piezoelectric structures and devices are of engineering and scientific significance.In this paper,a fourth-order phase-field fracture model for piezoelectric solids is developed based on the Hamilton principle.Three typical electric boundary conditions are involved in the present model to characterize the fracture behaviors in various physical situations.A staggered algorithm is used to simulate the crack propagation.The polynomial splines over hierarchical T-meshes(PHT-splines)are adopted as the basis function,which owns the C1continuity.Systematic numerical simulations are performed to study the influence of the electric boundary conditions and the applied electric field on the fracture behaviors of piezoelectric materials.The electric boundary conditions may influence crack paths and fracture loads significantly.The present research may be helpful for the reliability evaluation of the piezoelectric structure in the future applications.

The Semi-Microscopic Description of the Gross Resonant Structure of ^(16)O+^(16)O system

Within the framework of nuclear molecular orbital model,the semi-micro-scopic description of the gross resonant structure of 16O+16O system is given.The pre-sent result is comparable to other theoretical results which are in agreement with the ex-isting experimental data.

Calibration of a Microscopic Model of an Urban Traffic Network

Traffic simulation models have the potential to provide an objective, cost-effective and flexible approach to assessing system design, traffic operations and management strategies. In that regard, the calibration and validation of simulation model is crucial for appropriate decision making process. This paper presents an application of microscopic simulation model calibration and validation procedure for a multimodal urban traffic network. Model is developed by VISSIM and VISSIG software tools.

Application of a microscopic optical potential of chiral effective field theory in (p, d) transfer reactions

The microscopic global nucleon–nucleus optical model potential(OMP)proposed by Whitehead,Lim,and Holt,the WLH potential(Whitehead et al.,Phys Rev Lett 127:182502,2021),which was constructed in the framework of many-body per-turbation theory with state-of-the-art nuclear interactions from chiral effective field theory(EFT),was tested with(p,d)transfer reactions calculated using adiabatic wave approximation.The target nuclei included both stable and unstable nuclei,and the incident energies reached 200 MeV.The results were compared with experimental data and predictions using the phenomenological global optical potential of Koning and Delaroche,the KD02 potential.Overall,we found that the micro-scopic WLH potential described the(p,d)reaction angular distributions similarly to the phenomenological KD02 potential;however,the former was slightly better than the latter for radioactive targets.On average,the obtained spectroscopic factors(SFs)using both microscopic and phenomenological potentials were similar when the incident energies were below approxi-mately 120 MeV.However,their difference tended to increase at higher incident energies,which was particularly apparent for the doubly magic target nucleus 40Ca.

Microscopic phase-field study on aging behavior of Ni_(75)Al_(17)Zn_8 alloy

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.