Modified Embedded Atom Method Research Articles

Study on the Irradiation Evolution and Radiation Resistance of PdTi Alloys.

Medium-entropy alloys (MEAs) exhibit exceptional mechanical properties, thermal properties, and irradiation resistance, making them promising candidates for aerospace and nuclear applications. This study utilized molecular dynamics simulations to examine the defect behavior in PdTi alloys under various irradiation conditions. Simulations were performed using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) with the modified embedded-atom method (MEAM) potential to describe interatomic interactions. Various temperatures, primary knock-on atom (PKA) energies, and elemental ratios were tested to understand the formation and evolution of defects. The results show that compared to pure Pd, PdTi alloys with increased entropy exhibit significantly enhanced irradiation resistance at higher temperatures and PKA energies. This study explored the impact of different elemental ratios, including Pd, PdTi1.5, PdTi, and Pd1.5Ti. Findings indicate that increasing the Pd concentration enhances the alloy's irradiation resistance, improving mobility and recombination rates of defect clusters. A one-to-one Pd-to-Ti ratio demonstrated optimal performance. Temperature analysis revealed that at 300 K and 600 K, PdTi alloys exhibit excellent irradiation resistance at a PKA energy of 30 keV. However, as the temperature rises to 900 K, the irradiation resistance decreases slightly, and at 1200 K, the performance is likely to decline further. This study offers some useful insights into the irradiation evolution and radiation resistance of PdTi medium-entropy alloys, which may help inform their potential applications in the nuclear field and contribute to the further development of MEAs in this area.

Neural network interatomic potential-driven analysis of phase stability in Ti–V alloys at the atomistic scale

The evolution of the ω phase in titanium–vanadium (Ti–V) alloys is critical for their mechanical properties, particularly in aerospace and biomedical applications. This study employs a Rapid Artificial Neural Network (RANN) potential to model the ω phase evolution at the atomistic level, demonstrating a high degree of consistency with experimental observations, unlike the Modified Embedded Atom Method (MEAM), which fails to capture this phase transformation accurately. RANN simulations replicate key phenomena such as the nucleation of α precipitates at ω/β interfaces and accurate lattice orientations, enhancing our understanding of phase stability and transformation kinetics. The findings affirm that RANN potentials can significantly improve the prediction accuracy of complex material behaviors, offering a powerful tool for designing advanced materials with tailored properties such as solute effect in various stacking fault energies. This approach not only bridges the gap between theoretical predictions and empirical data but also sets a new direction for future research in materials science, emphasizing the integration of machine learning techniques in the development and optimization of new alloys.

Effect of alloying element content, temperature, and strain rate on the mechanical behavior of NbTiZrMoV high entropy alloy: A molecular dynamics study

High entropy alloys (HEAs) have drawn attention among researchers due to their excellent mechanical properties at low and high temperatures, which pave the way for their numerous applications in various sectors. In this study, we have investigated the effect of temperature and strain rate on the mechanical properties of single crystal equimolar NbTiZrMoV alloy, a refractory HEA (RHEA), using molecular dynamics simulation with the help of a newly developed modified embedded atom method (MEAM) potential. Uniaxial tensile simulations were conducted along x-direction at temperatures between 77 K and 600 K, with temperature intervals of 100 K, and at strain rates of 0.001 ps−1, 0.005 ps−1, 0.025 ps−1, and 0.125 ps−1. Stress-strain curves were plotted from the simulation data, and different tensile properties of the alloy were calculated from the graph. This study suggests that the tensile strength and the elastic modulus of the HEA decrease with increasing temperature as the materials become soft at higher temperatures. Strain rate improves the tensile mechanical properties with increasing rate due to the lack of required time for atom rearrangement and dislocation entrapment requiring higher stresses to continue deformation. Ultimately, the tensile characteristics of the HEA are shown to be influenced by the content of alloying elements. Specifically, Mo content has a rising effect, and Nb content is having a reducing impact on the tensile properties of NbTiZrMoV HEA. The study provides insights into the mechanical properties of NbTiZrMoV HEA, which could inform its applications in various sectors due to its promising mechanical features at different temperatures and strain rates.

Atomistic study of intermetallics of Fe–Al–Zn system and their interfacial properties

Galvanizing is an important industrial process to improve the corrosion resistance of advanced high strength steels (AHSSs) that are vital for automotive industries. During galvanizing, nanoscale intermetallic phases with complex crystal structures are formed at the interface between the steel substrate and the zinc overlay. To better understand the nanoscale structures and the interfacial properties between the intermetallics, in this work, we develop a second nearest neighbor (2NN) Fe–Al–Zn ternary Modified Embedded Atom Method (MEAM) potential to describe the crystal structures of the intermetallics, i.e. Fe3Al8, Fe4Zn9 and FeZn13 and to calculate the interfacial structure and energy between them. The developed MEAM potential describes well the complex crystal structures and can be used to investigate the interfacial properties that are difficult to obtain from experiments. The Fe4Zn9, FeZn13 surface energies; the Fe–Fe4Zn9, Fe–FeZn13, Fe3Al8–FeZn13 interfacial energies; and the work of adhesion are calculated with the developed MEAM potential. The results show that FeZn13 crystal orientation has an insignificant effect on the FeZn13 surface energy and the Fe–FeZn13 interfacial energy. A negative interfacial energy is obtained for the Fe–Fe4Zn9 and the Fe–FeZn13 interface. The lowest interfacial energy is obtained in the {100}Fe case. The interfacial energy of Fe3Al8–FeZn13 depends on the surface termination of Fe3Al8 and FeZn13. A low interfacial energy is obtained when the surface termination of Fe3Al8 and FeZn13 are both Fe rich. In contrast, when the surface termination of Fe3Al8 is Al rich or the surface termination of FeZn13 is Zn rich, no low energy, stable interface can be formed between the two phases.

Microstructural Evolution of Al under Computational Analysis of Uniaxial [100] Compression

The strain rate exerts a profound influence on the mechanical characteristics of nanomaterials. To investigate this phenomenon, the molecular dynamics approach was employed to examine the impact of uniaxial compression along the [100] crystallographic direction in monocrystalline Al. The purpose of this research was to determine the differences in reactions observed during the elastic and plastic phases. It employed the Embedded Atom Method (EAM) as well as the Modified Embedded Atom Method (MEAM) potentials at 300 K. A comparative analysis of the outcomes from these potentials demonstrated considerable disparities. The results encompassed the percentage distribution of crystal structures (fcc, hcp, bcc, and others) as well as their atomic configurations. Several analytical factors were examined, including the strain-stress curve, the radial distribution function (RDF), the common neighbor analysis (CAN). The applied MEAM potential represents a subsequent occurrence of transitions following EAM, encompassing both increasing and decreasing phase transitions.

Atomistic investigation of effect of alloying on mechanical properties and microstructural evolution of ternary FeCo-X (X = V, Nb, Mo, W)

This atomistic simulation study delves into the impact of V, Nb, Mo, and W on the mechanical properties of equiatomic FeCo, employing the modified embedded atom method (MEAM). An analysis of individual effects on antiphase boundary (APB) energies reveals a consistent reduction along preferred slip planes, except for Nb. Monte Carlo-molecular dynamics (MC-MD) simulations were used to explore the diffusion behavior of these solutes, highlighting their dynamic interactions and preference to migrate into the grain boundaries (GB).Tensile simulations conducted on nanocrystalline (NC) models oriented in different directions unveil comparable stress–strain curves, displaying continuous yielding with a humpy yield curve that varies with the straining orientation. Notably, W emerged as the most effective addition enhancing the ultimate tensile strength (UTS). Microcrack nucleation development differ depending on the straining direction. In binary FeCo and in the alloy with Mo additions, void development was observed at grain boundary (GB) triple junctions, while with V and W additions, it occurred at the intersection of a slip band and a GB, with limited propagation in both scenarios. In contrast, Nb additions show enhanced stress accommodation through slip band formation within grains, preventing microcrack development. These discoveries offer valuable insights on the impact of alloying elements on the mechanical behavior of ternary FeCo-X (X = V, Nb, Mo, W) alloys.

Theoretical investigation on the solid-liquid phase transition of gallium through free energy analysis.

Gallium, renowned for its notably low melting point and unique property of becoming liquid at room temperature, is a valuable constituent in phase change materials. In this study, we investigate the solid-liquid phase transition of gallium using the modified embedded atom method (MEAM) potential. It addresses the technique to compute the free energy difference between the solid and liquid without using a reference state. We examine various thermodynamic and dynamic properties, including density, specific heat capacity, diffusivity, and radial distribution functions. We compute the coexistence temperature of the solid-liquid phase transitions of gallium from free energy analysis. This information is crucial for understanding the behavior of the material under different pressure conditions and can be valuable for various applications, such as materials processing and high-pressure studies. The analysis, findings, and insights of the present work will be of great significance to the broad scientific and engineering communities in the field of phase transformation of materials. A series of molecular dynamics(MD) simulations were conducted using the LAMMPS software packages. The gallium atoms are modeled using the modified embedded atom method (MEAM) potential. To accurately predict the solid-liquid phase transitions of gallium, we calculated free energy by employing the "constrained λ integration" method, coupled with multiple histogram reweighting (MHR). The solid-liquid coexistence line is determined through the Gibbs-Duhem integration technique.

Comparison and Assessment of Different Interatomic Potentials for Simulation of Silicon Carbide.

Interatomic potentials play a crucial role in the molecular dynamics (MD) simulation of silicon carbide (SiC). However, the ability of interatomic potentials to accurately describe certain physical properties of SiC has yet to be confirmed, particularly for hexagonal SiC. In this study, the mechanical, thermal, and defect properties of four SiC structures (3C-, 2H-, 4H-, and 6H-SiC) have been calculated with multiple interatomic potentials using the MD method, and then compared with the results obtained from density functional theory and experiments to assess the descriptive capabilities of these interatomic potentials. The results indicate that the T05 potential is suitable for describing the elastic constant and modulus of SiC. Thermal calculations show that the Vashishta, environment-dependent interatomic potential (EDIP), and modified embedded atom method (MEAM) potentials effectively describe the vibrational properties of SiC, and the T90 potential provides a better description of the thermal conductivity of SiC. The EDIP potential has a significant advantage in describing point defect formation energy in hexagonal SiC, and the GW potential is suitable for describing vacancy migration in hexagonal SiC. Furthermore, the T90 and T94 potentials can effectively predict the surface energies of the three low-index surfaces of 3C-SiC, and the Vashishta potential exhibits excellent capabilities in describing stacking fault properties in SiC. This work will be helpful for selecting a potential for SiC simulations.

Atomistic mechanism of AlCu thin film alloy growth on trenched Si substrate

Molecular dynamics simulation was employed to study the growth mechanisms of an AlCu thin film on a trenched Si(001) substrate. The atomic interactions between Al, Cu, and Si atoms were described by using the Modified Embedded Atom Method (MEAM). This investigation focused on examining the effect of both incident energy and trench heights on the structure, and the morphology of deposited AlCu thin film. The results reveal that the growth mode follows an island mode, and the AlCu film surface exhibits both non-flat and non-uniform texture. The increase in the trench height leads to a more pronounced change in surface morphology and roughness. However, a higher incident energy can significantly reduce the surface roughness due to the mobility of deposited atoms. In addition, a mixing region was observed at the interface between the film and substrate. It is revealed that increasing the incident energy leads to deeper penetration of Al and Cu atoms into the substrate. More importantly, Al atoms penetrate deeper than the Cu atoms. On the other hand, deposition on a trench with 15 monoatomic layers leads to the formation of voids in the film. However, these voids disappear with higher incident energy. The microstructural evolution during deposition film was also analyzed based on the radial distribution function. The results of this function indicate that changes in trench height and the energy of incident adatoms do not significantly influence the structure of the film.

Effect of cooling rate on solidification points and atomic structures of metal nanoclusters: a molecular dynamics simulation study

In this work, the micro-structural evolution during the solidification process of three metal nanoclusters (copper, nickel, and silver) containing 2048 atoms each, subjected to different cooling rates are investigated. Molecular dynamics (MD) simulations in conjunction with modified embedded atom method (MEAM) potentials have been employed to carry out the work. For different cooling rates, the solidification points of the nanoclusters are estimated from the variation in average potential energy of the systems during the crystallization process, and the structural evolutions are analysed by utilising radial distribution function and common neighbour analysis method. The results advocate that the cooling rate has a profound impact on the structures of the solidified nanoclusters. The critical cooling rate for each nanocluster has been captured, where a glassy/amorphous structure is observed. Polycrystalline nano-structures (consisting of amorphous, FCC and HCP) are observed below these critical cooling rates and the number of close-packed structures (FCC, HCP) are found to decrease with the increase in cooling rate. The findings of this work would be helpful in various practical applications of the metal nanoclusters, where the structure of nanoclusters directly affect.

Development of U-Zr-Xe ternary interatomic potentials appropriate for simulation of defect and Xe behaviors in U-Zr system

U-10Zr metallic fuel (alloys of U with 10 wt% Zr) is considered as a potential candidate for fast reactors due to its excellent performance. However, the fission gas swelling has a significant impact on its properties and prevents it from reaching higher burnup. To gain a deeper understanding of the fission gas swelling mechanism, molecular dynamics simulations based on interatomic potentials are underway to fill the key knowledge gaps. In this work, two modified embedded-atom method (MEAM) potentials are developed for the U-Zr system with Xe, one for α-U-Zr and δ-UZr2, and the other for γ-U-Zr. The parameters of the potentials are determined by fitting the material properties from experiments or density functional theory (DFT) calculations. It is verified that the potentials can reproduce well the lattice constants, elastic constants, point defects, surface energy, and the melting point of U. In addition, the lattice constants, elastic constants, cohesive energy, and point defect formation energy of Zr are in good agreement with the experimental and DFT results. For the alloy system, the typical defect properties of Zr and Xe in U, as well as the formation energy and elastic constant of δ-UZr2 are close to the DFT. The lattice constant, linear thermal expansion, and mixing enthalpy of γ-U-Zr alloy are following the experimental values. The results show that the obtained potentials are suitable for simulating the defect evolution and Xe behaviors in the U-Zr system.

Modified embedded atom method interatomic potential for FCC γ-cerium

As interest in Cerium containing alloys and Al-Ce alloys in particular grows, the need to generate predictions of mechanical, thermodynamic and transport properties across a compositional space becomes more pronounced. The absence of a reliable interaction potential to be used in classical molecular dynamics (MD) simulation of γ-Ce is a fundamental bottleneck to subsequent alloy simulation. In this work, a Modified Embedded Atom Method (MEAM) potential to be used in MD simulation for γ-Ce has been generated. The parameterization process involved two steps. First, the iterative Latin hypercube sampling (LHS) method was used to generate MEAM parameter sets based on an automated optimization of energies and forces relative to a training set of small configurations evaluated through Density Functional Theory (DFT). Second, a human-guided optimization in that local parameter space was performed to refine the parameters to satisfy an array of mechanical, thermodynamic and transport properties available from the experimental literature. When used in an MD simulation, the resulting potential provides excellent estimates of all tested material properties across a broad temperature range. This γ-Ce potential, when combined with existing MEAM potential for Al, will form the necessary foundation for the subsequent development of a mixture potential, enabling the simulation of Al-Ce and Al-Ce-X alloys.

A Molecular Dynamics Study of Nucleation and Grain Growth of Novel Al-15Mg<sub>2</sub>Si-4.5Si Composite during Rapid Cooling Based Semi Solid Slurry Preparation

Owing to their several attractive features such as high hardness, high elastic modulus, light weight, high strength to weight ratio, high thermal conductivity, and high temperature strength, composites from Al-Mg2Si family offers promise towards deployment in several industries such as automobile, aerospace, marine, defence and electronic. The present molecular dynamics (employing LAMMPS) based simulation study is one of the first attempt to investigate the nucleation and grain growth mechanisms of Mg2Si phase at atomic level in case of novel Al-15Mg2Si-4.5Si composite, during semi-solid processing. Modified embedded atom method (MEAM) potential has been used to study the atomic interactions in the composite. Reaching the melt state at 1000 K, the temperature of the system is first decreased from 1000 K to 853 K and then the system is held at 853 K for 100 ps. The simulations are performed with three different cooling rates. With lowering of temperature, randomly distributed Mg and Si atoms form atomic clusters at arbitrary locations within the system, which is the nucleation stage for Mg2Si phase formation. Cluster size, radial distribution function has been used to investigate the structural evolution of Mg-Si clusters. Cooling rate significantly influences the grain size as well as the grain growth kinetics. The information about the thermodynamic state of the system has been revealed by extracting the values of internal energy, enthalpy, specific heat. during the slurry preparation and isothermal holding stages. The growth mechanism of Mg2Si nucleus has been characterized from the temporal variation of (Mg + Si) atoms taking part in the cluster formation. Power-law variation is observed in the cooling stage whereas a linear variation is observed in the isothermal stage.

Dissociation of edge and screw pyramidal I and II dislocations in magnesium

Pyramidal dislocations in magnesium (Mg) and other hexagonal close-packed metals play an important role in accommodating plastic strains along the c-axis. Bulk single crystal Mg only presents very limited plasticity in c-axis compression, and this behavior was attributed to out-of-plane dissociation of pyramidal dislocations onto the basal plane and resulted in an immobile dislocation configuration. In contrast, other simulations and experiments reported in-plane dissociation of pyramidal dislocations on their slip planes. Thus, the core structure and mode of dissociation of pyramidal dislocations are still not well understood. To better understand the dissociation behavior of pyramidal dislocations in Mg at room temperature, in this work, atomistic simulations were conducted to investigate four types of pyramidal dislocations at 300 K: edge and screw Py-I on {101¯1}, edge and screw Py-II on {112¯2} by using a modified embedded atom method (MEAM) potential for Mg and anisotropic elasticity dislocation model. The results show that when energy minimization was performed before relaxation, in-plane dissociation of edge dislocations on respective pyramidal plane could be obtained at room temperature for all four types of dislocation. Without energy minimization, the edge dislocations dissociated out-of-plane onto the basal plane. Calculations of potential energy and hydrostatic stress of individual atoms at the edge dislocation core show that the extraordinarily high energy and atomic stresses in the as-constructed dislocation structures caused the out-of-plane dissociation onto the basal plane. The core structures of all four types of pyramidal dislocation after in-plane dissociation were analyzed by computing the distribution of the Burgers vector.

Machine learning-assisted MD simulation of melting in superheated AlCu validates the Classical Nucleation Theory

The validity of the Classical Nucleation Theory (CNT), the standard tool for describing and predicting nucleation kinetics in metastable systems, has been under scrutiny for almost a century. While the CNT is commonly employed to describe liquid → crystal and liquid ↔ vapor phase transitions, its application to the crystal → liquid case has been limited because of the experimental challenges in achieving superheating states and detecting homogeneous liquid nucleation. In this study, we performed comprehensive molecular dynamics (MD) simulations of spontaneous melting of a superheated AlCu crystal under atmospheric pressure at five temperatures, covering a superheating range of T/TL = 1.1–1.3, where TL is the liquidus temperature. Two realistic AlCu models were investigated: one described by the modified embedded atom method (MEAM) and the other by an interatomic potential generated by an artificial neural network machine learning (ML) approach, extensively trained on an ab initio dataset of liquid and crystal configurations. Fifty independent melting events were simulated at each temperature. By analyzing the distribution of melting times using the Poisson law, the homogeneous nucleation rate was determined through the mean lifetime method. Additionally, the Zeldovich factor, critical nucleus size, and work of formation were obtained using the mean first-passage time method, utilizing the disorder parameter based on atomic displacements (liquid-like atoms in the superheated crystal) as the reaction coordinate. Also, the effective atomic transport coefficient across the metastable crystal/critical liquid nucleus interface was determined by MD simulations as the interfacial attachment coefficient for nuclei growth rates. Using these simulation-generated data, the theoretical nucleation rates were calculated by the CNT with no fitting parameters. We found excellent agreement between the theoretically and MD-computed liquid nucleation rates for both MEAM and ML crystals. Notably, the effective solid-liquid interfacial free energy value obtained from the MD data aligns with its recent experimental measure. Moreover, the CNT qualitatively and quantitatively described the underlying details of liquid drop nucleation in our ML solid, unprecedentedly and accurately reproducing the kinetic prefactor and the size, formation energy, and growth rate of the critical nuclei. Thus, the melting of the AlCu model created through machine learning-processed quantum calculations, that is, not relying on hand-crafted interatomic potential functions, was successfully described by the CNT phenomenological formalism, without any adjustable parameters. This finding confirms the CNT as a very reliable descriptor of homogeneous nucleation in the superheated AlCu alloy and generalizes this theory as a powerful tool for analyzing and predicting the kinetics of crystal-liquid transitions.

Mechanical properties of aluminum through electronic- and atomic-scale simulations

Implementing the integrated computational materials engineering methodology in modeling plastic deformation processes and associated phenomena can provide a unique opportunity for a deeper study of material behavior at smaller scales and result in more precise and accurate predictions. This study presents a multiscale modeling framework linking two different length scales – namely, the electronic and the atomic scale – to investigate the mechanical properties of pure aluminum (Al) and to achieve the required parameters and information for higher scales. At the electronic scale, the elastic properties and interfacial energies for aluminum were garnered from density functional theory simulations to calibrate the modified embedded atom method (MEAM) potentials required for atomic simulations. The calculation for the generalized stacking fault energy resulted in an intrinsic stacking fault energy of 185.5 mJ/m2. Using the parameter calculated at the electronic scale as well as the MEAM potential parameters, the edge dislocation mobility of aluminum from molecular dynamics simulations was calculated at the atomic scale (nano). A drag coefficient of 7.3 × 10−5 Pa s was computed at 300 K. The dependency of the drag coefficient on the temperature was also studied, and the results showed that the velocity linearly depended on τ/T up to 0.4 MPa/K.

Grain-boundary thermodynamics with artificial-neural-network potential: Its ability to predict the atomic structures, energetics, and lattice vibrational properties for Al

An artificial neural network (ANN) potential for Al, trained with density-functional-theory (DFT) data, is constructed to accurately predict lattice vibrational properties and thermodynamics of grain boundaries (GBs) in Al. The ANN potential is demonstrated to accurately predict not only atomic structures and energetics of the GBs at 0 K but also partial phonon densities of states and vibrational entropies, even for GBs absent in the training data sets. In addition, their total potential energies and atomic forces by DFT at elevated temperatures up to 800 K can also be well reproduced by molecular dynamics with the ANN potential. In contrast, a modified embedded atom method (MEAM) potential shows larger errors in phonon frequencies and atomic forces for atoms at GBs, as well as in the bulk, than the ANN potential. The MEAM potential is thus likely to be inadequate to quantitatively predict thermodynamic properties of GBs, particularly at high temperature. The present ANN potential is also applied to systematically examine thermodynamic stability of asymmetric tilt GBs. It is predicted that for the \ensuremath{\Sigma}9 system, the GB free-energy profile as a function of inclination angle exhibits a cusp at elevated temperatures, due to its larger vibrational entropies of asymmetric tilt GBs than those of \ensuremath{\Sigma}9 symmetric tilt GBs.

A Modified Embedded-Atom Method Potential for a Quaternary Fe-Cr-Si-Mo Solid Solution Alloy

Ferritic-martensitic steels, such as T91, are candidate materials for high-temperature applications, including superheaters, heat exchangers, and advanced nuclear reactors. Considering these alloys' wide applications, an atomistic understanding of the underlying mechanisms responsible for their excellent mechano-chemical properties is crucial. Here, we developed a modified embedded-atom method (MEAM) potential for the Fe-Cr-Si-Mo quaternary alloy system-i.e., four major elements of T91-using a multi-objective optimization approach to fit thermomechanical properties reported using density functional theory (DFT) calculations and experimental measurements. Elastic constants calculated using the proposed potential for binary interactions agreed well with ab initio calculations. Furthermore, the computed thermal expansion and self-diffusion coefficients employing this potential are in good agreement with other studies. This potential will offer insightful atomistic knowledge to design alloys for use in harsh environments.

The Effect of Interatomic Potentials on the Nature of Nanohole Propagation in Single-Crystal Nickel: A Molecular Dynamics Simulation Study

Based on a molecular dynamics (MD) simulation, we investigated the nanohole propagation behaviors of single-crystal nickel (Ni) under different styles of Ni–Ni interatomic potentials. The results show that the MEAM (the modified embedded atom method potential) potential is best suited to describe the brittle propagation behavior of nanoholes in single-crystal Ni. The EAM/FS (embedded atom method potential developed by Finnis and Sinclair) potential, meanwhile, is effective at characterizing the plastic growth behavior of nanoholes in single-crystal Ni. Furthermore, the results show the difference between the different styles of interatomic potentials in characterizing nanohole propagation in single-crystal Ni and provide a theoretical basis for the selection of interatomic potentials in the MD simulation of Ni crystals.

Simulation of thermal decomposition of γ′-Fe4N using molecular dynamics method

α″-Fe16N2 is a promising environmentally friendly rare-earth-free permanent magnet material with ultra-high saturation magnetization. Recent research has demonstrated experimentally through a thermally quenching treatment using γ′ phase Fe4N as a precursor to synthesize α″-Fe16N2 in bulk format. In this research using Molecular Dynamics (MD) simulation, we investigated the γ′-Fe4N phase thermal decomposition process and the potential phase transition from face center cubic (fcc)-phase to body center tetragonal (bct)-phase. As nitrogen concentration is higher in γ′-Fe4N (5.9 wt. %) than that in α′-Fe8N or α″-Fe16N2 (3 wt. %), Nitrogen bond formation through atom diffusion is studied with a “Nitrogen-rich” grain boundary (GB) model to find out whether lower-Nitrogen content bct Fe–N solid solution can be formed. Modified Embedded Atom Method (MEAM) interatomic potential of Fe–N system is applied. Post-processing including Nitrogen bond mapping/tracking is also performed for the thermostat-controlled heating and quenching simulation process. We also applied virtual XRD computation to characterize the material crystallographic texture before and after the thermal treatment.