Bcc Binary Alloys Research Articles

LÍ THUYẾT BIẾN DẠNG ĐÀN HỒI CỦA MÀNG MỎNG HỢP KIM XEN KẼ NHỊ NGUYÊN LẬP PHƯƠNG TÂM KHỐI TỪ PHƯƠNG PHÁP THỐNG KÊ MÔMEN

The article presents the theory of elastic deformation and elastic wave propagation velocity of BCC binary interstitial alloy’s thin film based on the statistical moment method. Metal’s films and bulk interstitial alloys are specific cases of interstitial alloy’s films in this theory. The obtained theoretical results are applied to W and WSi films, where calculated results are compared with other calculations and experimental data.

Thermodynamic and elastic properties of tungsten and tungsten silicide

We present thermodynamic and elastic theory for BCC metal and binary interstitial alloy established by the statistical moment method (SMM) and perform numerical calculations for the silicon concentration, pressure and temperature dependences of nearest neighbor distance, volume, thermal expansion coefficient, heat capacities at constant volume and at constant pressure, Debye temperature, Gruneisen parameter, isothermal elastic modulus, bulk modulus, shearing modulus, elastic constants and longitudinal wave velocity for W and WSi under temperature up to 3600 K, pressure up to 100 GPa and silicon atom concentration up to 5%. The SMM numerical calculations for W are compared with experiments and other calculations. The SMM calculated results for WSi are predictive, orienting experimental results in the future.

Young Modulus, Maximum Real Stress and Elastic Deformation Limit of W and WSi from Statistical Moment Method

We present the theory of nonlinear and elastic defomation for BCC metal and binary interstitial alloy builded on the basis of a statistical moment method and our numerical calculations for W and WSi depending on temperature, pressure and interstitial atom concentrations. Our numerical calculations for Young modulus of W are compared with experiments and our other numerical calculations are new and predictic.

Elastic deformation and elastic wave velocity of iron and its binary interstitial alloys: Temperature, pressure and interstitial atom concentration dependences

Based on the BCC binary interstitial alloy model with the condition that the interstitial atom concentration is very small compared to the main metal atom concentration and the elastic deformation theory of this alloy obtained on the basis of statistical moment method, we perform numerical calculations for elastic deformation quantities such as the elastic moduli E, K, G, the elastic constants C11, C12, C44, the longitudinal wave velocity Vd and the transverse wave velocity Vn of metal Fe and alloys FeSi, FeC, FeH. Numerical results for Fe are in good agreement with experiments and other calculations. The temperature and pressure dependence of the elastic deformation quantities for FeSi, FeC, FeH are similar to those for Fe. The elastic deformation quantities of FeSi, FeC, FeH in the range from 0 to 1000 K, from 0 to 10 GPa and from 0 to 5% of silicon (carbon, hydrogen) atom concentrations predict experimental results.

STUDY ON ELASTIC PROPERTY OF STAINLESS STEEL UNDER PRESSURE

The paper presents analytic expressions of the Helmholtz free energy and characteristic elastic deformation quantities such as the elastic moduli E, K, G and the elastic constants C11, C12, C44 for BCC interstitial and substitutional alloy with four components are determined by the statistical moment method. The obtained elastic quantities depend on temperature, pressure, the concentration of interstitial atoms, and the concentration of substitutional atoms. This is the elastic deformation theory of BCC interstitial and substitutional alloy with four components published for the first time. The elastic deformation theories of BCC metal, BCC binary interstitial alloy, BCC binary substitutional alloy, and BCC ternary interstitial and substitutional alloy are limit cases of the elastic deformation theory of BCC substitutional and interstitial alloy with four components. Our numerical calculations of the obtained theoretical results for metal Fe and alloy FeSi are in good agreement with other calculations and experiments. Other numerical calculations for alloys FeCr, FeNi, FeCrSi, FeNiSi, FeCrNiSi (some atoms Fe are substituted by atoms Cr and some other atoms Fe are substituted by atoms Ni) called stainless steels predict and orient experimental results in the future. Our numerical calculations for alloy FeCrNiSi are published for the first time.

Calculation of formation enthalpies and dilute heats of bcc–bcc binary alloys by modified ones of EAM potentials

The formation enthalpies and the dilute heats of body-centered cubic–body-centered cubic (bcc–bcc) binary alloys are evaluated by employing the modified ones of the embedded atom method potentials for bcc metals. The modified embedded atom method (MEAM) potentials for bcc transition metals proposed by Jin et al. (Appl Phys A 120:189, 2015), Johnson’s alloy potential form, and Vegard’s law are applied to calculate the formation enthalpies in the whole composition range for 21 kinds of bcc–bcc binary alloys bearing bcc transition metals Cr, Fe, Mo, Nb, Ta, V, and W. Several formulas are suggested to calculate the dilute heats of the binary alloy solid solutions using the MEAM potentials for bcc transition metals and used in the evaluation of the dilute heats of 42 kinds of bcc–bcc binary alloy solid solutions. The present results of the formation enthalpies and the dilute heats for most bcc–bcc binary alloys are in mainly agreement with the experimental data and the calculations by the Miedema theory, as well as agree with the experimental data and the Miedema theory results better than the precedent MEAM results.

Predicting magnetization of ferromagnetic binary Fe alloys from chemical short range order

Among the ferromagnetic binary alloys, body centered cubic (bcc) Fe-Co is the one showing the highest magnetization. It is known experimentally that ordered Fe-Co structures show a larger magnetization than the random solid solutions with the same Co content. In this work, based on density functional theory (DFT) studies, we aim at a quantitative prediction of this feature, and point out the role of the orbital magnetic moments. Then, we introduce a DFT-based analytical model correlating local magnetic moments and chemical compositions for Co concentrations ranging from 0 to 70 at.%. It is also extended to predict the global magnetization of both ordered and disordered structures at given concentration and chemical short range orders. The latter model is particularly useful for interpreting experimental data. Based on these models, we note that the local magnetic moment of a Fe atom is mainly dictated by the Co concentration in its first two neighbor shells. The detailed local arrangement of the Co atoms has a minor effect. These simple models can fully reproduce the difference in magnetization between the ordered and disordered Fe-Co alloys between 30% and 70% Co, in good agreement with experimental data. Finally, we show that a similar model can be established for another bcc binary Fe alloy, the Fe-Ni, also presenting ferromagnetic interactions between atoms.

Ab initio modelling of vacancy–solute dragging in dilute irradiated iron-based alloys

The formation of solute–defect nanoclusters in RPV steels is the main cause of radiation induced embrittlement. Solute atoms may diffuse in the alloy by a vacancy drag mechanism, depending on the strength of interaction with point defects. A multifrequency model based on ab initio computed migration barriers was applied in order to investigate the possibility of solute drag in iron-based bcc binary alloys containing Ni, Cr, Cu or Mn, and the obtained solute diffusion coefficients were compared with previous experiments. The results show that Ni is expected to be dragged at temperatures below approximately 900K, while Cr and Mn are not involved in the dragging mechanism. As for Cu, the results are controversial because the computed migration barriers are strongly affected by the particular choice of the ab initio method.

Measuring atomic moment and magnetic order through magnetic linear dichroism with angular dependence studies of transition-metal alloys

Magnetic linear dichroism measurements allow the measurement of atomic moments and spin order in alloy magnetic systems with chemical specificity and surface sensitivity. The width of the dichroism spectrum is a measure of the atomic moment via the local exchange, while the dichroism amplitude is a measure of the elemental contribution to magnetic order in the alloy via the dipole selection rules. An analytical method has been introduced to accurately and systematically determine the dichroism width and amplitude in order to compare different alloy systems. Bcc and fcc binary alloys have been compared, and it is found that while the atomic moment is independent of the crystal structure and undergoes no collapse in moment, the magnetic order parameter collapses at the $\mathrm{NiFe}$ invar transition, as expected. Changing magnetic moments have been tracked with changing alloy composition, along with changes in the magnetic easy axis and Curie temperature, and are found to track the Slater-Pauling curve.

Surface composition of alloys via BFS atomistic Monte Carlo simulation

We have computed, via Monte Carlo atomistic simulation, the heats of segregation for the (1 0 0) surface of bcc binary alloys, including all combinations of V, Cr, Fe, Nb, Ta and W. Energetics are computed using the Bozzolo–Ferrante–Smith method for alloys, with and without atomistic relaxation. We discuss segregation trends in the context of the mechanisms believed to drive the segregation, and examine in more detail specific binaries in which the effects of these mechanisms are particularly evident.

Interstitial Hydrogen in BCC Binary Alloys: Site Occupancies and Transition Probabilities

The nature of interstitial sites, their spatial correlations as well as their occupation probabilities by H (or D) have been investigated in random bcc binary alloys. Sites of both octahedral and tetrahedral types have been taken into account assuming they were distinguishable one another on the basis of either the chemical composition of their first shell of neigbouring atoms or of the distribution of the two metallic species within this shell. Short-range repulsive interactions among H atoms have been accounted for in terms of the hard core model and expressions have been derived for the so-called selective blocking factors. The results of calculations have been used to predict the occurrence of anelastic relaxations due to H. A comparison of the theoretical predictions with experimental data available in the literature is presented.

Concentration overshooting caused by compositional relaxation in a one-dimensional bcc binary model alloy: a computer simulation on microscopic master equations

Concentration overshooting caused by compositional relaxation in a one-dimensional bcc binary model alloy: a computer simulation on microscopic master equations

Surface critical behavior of bcc binary alloys

The surface critical behavior of bcc binary alloys undergoing a continuous B2-A2 order-disorder transition is investigated in the mean-field (MF) approximation. Our main aim is to provide clear evidence for the fact that surfaces which break the two-sublattice symmetry generically display the critical behavior of the NORMAL transition, whereas symmetry-preserving surfaces exhibit ORDINARY surface critical behavior. To this end we analyze the lattice MF equations for both types of surfaces in terms of nonlinear symplectic maps and derive a Ginzburg-Landau model for the symmetry-breaking (100) surface. The crucial feature of the continuum model is the emergence of an EFFECTIVE ORDERING (``staggered'') SURFACE FIELD, which depends on temperature and the other lattice model parameters, and which explains the appearance of NORMAL critical behavior for symmetry-breaking surfaces.

Wetting Phenomena in bcc Binary Alloys

We study the influence of the surface orientation on the wetting behavior of bcc binary alloys, using a semiinfinite lattice model equivalent to a nearest-neighbor Ising antiferromagnet in an external magnetic field. This model describes alloys that exhibit a continuous B2–A2 order–disorder transition, such as FeAl or FeCo. For symmetry-breaking surfaces like (100), an effective ordering surface field g1≠0 emerges. Such a field not only crucially affects the surface critical behavior at bulk criticality, but also gives rise to wetting transitions below the critical temperature Tc. Starting from the mean-field theory for the lattice model and making a continuum approximation, a suitable Ginzburg–Landau model is derived. Explicit results for the dependence of its parameters (e.g., of g1) on the microscopic interaction constants are obtained. Utilizing these in conjunction with Landau theory, the wetting phase diagram is calculated.

Ordering Processes in FCC and BCC Binary Alloys: A Comparative Study

We study the problem of ordering kinetics in a binary alloy rapidly quenched through an order-disorder transition by Monte Carlo simulations. We consider two particular cases: (i) an AB bcc alloy relaxing from the disordered to an ordered B2 phase (e.g. FeAl) and (ii) an A 3 B fcc alloy relaxing from a disordered to an ordered L1 2 phase (e.g. Cu 3 Au). The alloys, that are supposed to contain a little concentration of vacancies, are modeled by means of a spin-1 Ising model. A modified Kawasaki dynamics in which only exchanges between atoms and vacancies are permitted, has been used in the simulations. The main differences in the behaviour of both systems during the coarsening regime are analyzed.

Interstitial Hydrogen in bcc Binary Alloys : Site Occupancies and Transition Probabilities

The nature of interstitial sites, their spatial correlations as weil as their occupation probabilities by H (or D) have been investigated in random bcc binary alloys. Sites of both octahedral and tetrahedral types have been taken into account assuming they were distinguishable one another on the basis of either the chemical composition of their first shell of neigbouring atoms or of the distribution of the two metallic species within this shell. Short-range repulsive interactions among H atoms have been accounted for in terms of the hard core model and expressions have been derived for the so-called selective blocking factors. The results of calculations have been used to predict the occurrence of anelastic relaxations due to H. A comparison of the theoretical predictions with experimental data available in the literature is presented.

Computer Simulation of Phase Decomposition Process Generating Precipitates Harder than Matrix

The Monte Carlo method combined with the static variational method is applied to a computer simulation on the phase decomposition process when a precipitate in a bcc binary alloy is elastically harder than the matrix. The present study is compared with our previous results that were obtained for the case of the same elastic constant of the precipitates as that of the matrix in our previous report. We have adopted the Jonson-type potentials as the interaction between the constituent elements, and have used three kinds of interaction potentials between solute atoms. We find an anisotropic structure in the alloy whose elastic constant of the precipitates is equivalent to the constant of the matrix. The alloy that has harder precipitates than the matrix shows an isotropic structure or a little anisotropic structure depending on the value of elastic constant of the precipitates. We presume that the isotropic structure is yielded because of the larger contribution of the interfacial energy than the elastic strain energy. Evidently the total energy of the alloy with isotropic clusters is lower than that with anisotropic clusters for every potential used in the present simulation. Therefore we conclude that the formation of anisotropic clusters is not due to the shape of precipitates with the minimum elastic energy but due to the dynamical process of phase decomposition concemed with nonlinear many body effect.

Statistico-thermodynamic properties of a binary alloy

We use the antiferromagnetic Ising model to obtain the equilibrium properties of a bcc binary alloy AxB1−x which undergoes an order–disorder transition. We use Monte Carlo simulations to obtain the μ–T phase diagram, for different values of x, and discuss how to interpret the results in relation to experiments.

母相より硬い析出物を生成する相分解過程の計算機シミュレーション

The Monte Carlo method combined with the static variational method is applied to a computer simulation on the phase decomposition process when a precipitate in a bcc binary alloy is elastically harder than the matrix. The present study is compared with our previous results that were obtained for the case of the same elastic constant of the precipitates as that of the matrix in our previous report. We have adopted the Jonson-type potentials as the interaction between the constituent elements, and have used three kinds of interaction potentials between solute atoms. We find an anisotropic structure in the alloy whose elastic constant of the precipitates is equivalent to the constant of the matrix. The alloy that has harder precipitates than the matrix shows an isotropic structure or a little anisotropic structure depending on the value of elastic constant of the precipitates. We presume that the isotropic structure is yielded because of the larger contribution of the interfacial energy than the elastic strain energy. Evidently the total energy of the alloy with isotropic clusters is lower than that with anisotropic clusters for every potential used in the present simulation. Therefore we conclude that the formation of anisotropic clusters is not due to the shape of precipitates with the minimum elastic energy but due to the dynamical process of phase decomposition concemed with nonlinear many body effect.

Antiphase domain growth in BCC metallic alloys via vacancies

We study by Monte Carlo simulation the influence of vacancies on the growth of antiphase domains after a quench of a BCC binary alloy. We find a powerlaw regime (R(t)∼t x withx depending on temperature and larger than the Allen-Cahn value 0.5. We have verified the scaling of the structure factor and performed a finite size analysis of the excess energy evolution and vacancy diffusion.