Search Results (17)

The mechanical response of high-entropy alloys (HEAs), specifically the FeNiCrCoAl HEA, was studied at both bulk and nanoparticle scales using molecular dynamics simulations. These simulations were performed using the LAMMPS software with an Embedded Atom Method (EAM) potential. The results show that Bulk HEAs exhibited enhanced hardening and plasticity, while in nanoparticles, distinct deformation patterns were observed, including nanotwin formation, V-shaped stacking fault planes, and intermittent dislocation activity due to free surface effects. The crystallographic orientation with respect to the compression significantly affected the deformation mechanisms, with the [100] direction favoring progressive hardening, while the [110] and [111] directions exhibited different stacking fault and dislocation dynamics. A detailed analysis using von Mises stress and dislocation analysis provided insights into the effects of scale on mechanical properties. Full article

Nanocomposites composed of Cu and Mo were investigated by means of molecular dynamics (MD) simulations to study the incoherent interface between Cu and Mo. In order to select an appropriate potential capable of accurately describing the Cu-Mo system, five many-body potentials were compared: three Embedded Atom Method (EAM) potentials, a Tight Binding Second Moment Approximation (TB-SMA) potential, and a Modified Embedded Atom Method (MEAM) potential. Among these, the EAM potential proposed by Zhou in 2001 was determined to provide the best compromise for the current study. The simulated system was constructed with two layers of Cu and Mo forming an incoherent fcc-Cu(111)/bcc-Mo(110) interface, based on the Nishiyama–Wassermann (NW) and Kurdjumov–Sachs (KS) orientation relationships (OR). The interfacial energies were calculated for each orientation relationship. The NW configuration emerged as the most stable, with an interfacial energy of 1.83 J/m², compared to 1.97 J/m² for the KS orientation. Subsequent simulations were dedicated to modeling Cu atomic deposition onto a Mo(110) substrate at 300 K. These simulations resulted in the formation of a dense layer with only a few defects in the two Cu planes closest to the interface. The interfacial structures were characterized by computing selected area electron diffraction (SAED) patterns. A direct comparison of theoretical and numerical SAED patterns confirmed the presence of the NW orientation relationship in the nanocomposites formed during deposition, corroborating the results obtained with the model fcc-Cu(111)/bcc-Mo(110) interfaces. Full article

Ta/Re layered composite material is a high-temperature material composed of the refractory metal tantalum (Ta) as the matrix and high-melting-point, high-strength rhenium (Re) as the reinforcement layer. It holds significant potential for application in aerospace engine nozzles. Developing the Ta/Re potential function is crucial for understanding the diffusion behavior at the Ta/Re interface and elucidating the high-temperature strengthening and toughening mechanism of Ta/Re layered composites. In this paper, the embedded atom method (EAM) potential function for tantalum/rhenium binary alloys (Ta-Re alloys) is derived using the force-matching method and validated through first-principles calculations and experimental characterization. The results show that for the lattice constant of a bcc structure containing 54 atoms, surface formation energies per unit area of Ta-Re alloys obtained based on the potential function are 12.196 Å, E₁₀₀ = 0.16 × 10⁻² eV, E₁₁₀ = 0.10 × 10⁻² eV, and E₁₁₁ = 0.08 × 10⁻² eV, with error values of 0.015 Å, 0.04 × 10⁻² eV, 0.02 × 10⁻² eV, and 0.01 × 10⁻² eV, respectively, compared with the calculations from first principles calculations. It is noteworthy that the errors in the average binding energies of Ta-rich (Ta_39Re20, where the number of Ta atoms is 39 and Re atoms is 20) and Re-rich (Ta₂₀Re₃₉, where the number of Ta atoms is 20 and Re atoms is 39) cluster atoms, calculated by the potential function and first-principles methods, are only 1.64% to 1.98%. These results demonstrate the accuracy of the constructed EAM potential function. Based on this, three compositions of Ta-Re alloys (Ta₄₈Re₆, Ta₃₀Re₂₄, and Ta₆Re₄₈; the numerical subscripts represent the number of atoms of each corresponding element) were randomly synthesized, and a comparative analysis of their bulk moduli was conducted. The results revealed that the experimental values of the bulk modulus showed a decreasing and then an increasing tendency with the calculated values, which indicated that the potential function has a very good generalization ability. This study can provide theoretical guidance for the modulation of Ta/Re laminate composite properties. Full article

Multi-element alloys (e.g., non-equiatomic FeMnCoCr alloys) have attracted extensive attention from researchers due to the breaking of the strengthen-ductility tradeoff relationship. Plenty of work has been conducted to investigate the ingredient-dependent deformation mechanism in these alloys in experiments. However, the atomic simulations on such parameter-related mechanisms are greatly limited with the lack of the related interatomic potentials. In this work, two interatomic potentials are developed within the embedded atom method (EAM) framework for Fe_80−xMn_xCo₁₀Cr₁₀ high-entropy alloys. The tunability of the cohesive energy-related martensitic transformation (MT) mechanism was comprehensively investigated using molecular dynamics (MD) through a series of unilateral crack configurations with different twin boundary spacings (TBs). It is noted that the main deformation mechanism around the crack tip is transformed from a martensitic transformation to dislocation activities (dislocation or twin) with the variation of different cohesive energies between face-centered cubic (fcc) and hexagonal close-packed (hcp) phases. Additionally, the introduction of twin boundaries significantly enhances the strength and toughness of the alloys. The newly developed interatomic potentials are expected to provide theoretical support for the related simulations, focusing the martensitic transformation mechanism on high-entropy alloys. Full article

Voids in face-centered cubic (fcc) metals are commonly assumed to form via the aggregation of vacancies; however, the mechanisms of vacancy clustering and diffusion are not fully understood. In this study, we use computational modeling to provide a detailed insight into the structures and formation energies of primary vacancy clusters, mechanisms and barriers for their migration in bulk copper, and how these properties are affected at simple grain boundaries. The calculations were carried out using embedded atom method (EAM) potentials and density functional theory (DFT) and employed the site-occupation disorder code (SOD), the activation relaxation technique nouveau (ARTn) and the knowledge led master code (KLMC). We investigate stable structures and migration paths and barriers for clusters of up to six vacancies. The migration of vacancy clusters occurs via hops of individual constituent vacancies with di-vacancies having a significantly smaller migration barrier than mono-vacancies and other clusters. This barrier is further reduced when di-vacancies interact with grain boundaries. This interaction leads to the formation of self-interstitial atoms and introduces significant changes into the boundary structure. Tetra-, penta-, and hexa-vacancy clusters exhibit increasingly complex migration paths and higher barriers than smaller clusters. Finally, a direct comparison with the DFT results shows that EAM can accurately describe the vacancy-induced relaxation effects in the Cu bulk and in grain boundaries. Significant discrepancies between the two methods were found in structures with a higher number of low-coordinated atoms, such as penta-vacancies and di-vacancy absortion by grain boundary. These results will be useful for modeling the mechanisms of diffusion of complex defect structures and provide further insights into the structural evolution of metal films under thermal and mechanical stress. Full article

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. Full article

The formation of intermetallic compounds (IMC) at the Al/Fe interface determined the mechanical property of steel-aluminum welded joint. To understand the interfacial microstructure evolution and relate diffusion mechanism of atoms cross the Al/Fe interface, the effect of welding parameters on the interfacial IMC was studied, and the molecular dynamics method (MD) was used to simulate the diffusion process of Al and Fe atoms. Four temperatures (950 K, 1000 K, 1050 K, and 1100 K) were selected in the simulation model. The interfacial IMC are distributed in a laminar pattern, and their physical phases are mainly composed of Fe₂Al₅, controlling the Al/Fe atomic ratio of 5:2 in the IMC configuration, the Embedded Atom Method (EAM) potential is used to describe the interactions between Al and Fe atoms. In the Al-Fe system IMC conformation, the mean square displacement and diffusion (MSD) coefficient of Al atoms at different temperatures were small, and the main diffusion path is the Al atoms across the IMC conformation into the Fe crystal structure. The diffusion in the IMC conformation was mainly along the direction perpendicular to the interface. The diffusion mechanisms were mainly vacancy diffusion and interstitial diffusion mechanisms. Full article

Effects of different pressures on the isothermal-solidification process of pure Al were studied by molecular dynamics (MD) simulation using the embedded-atom method (EAM). Al was first subjected to a rapid-cooling process, and then it was annealed under different pressures conditions. Mean first-passage times (MFPT) method, Johnson-Mehl-Avrami (JMA) law, and X-ray diffraction (XRD) simulation analysis method were used to qualify the solidification- kinetic processing. Nucleation rate, critical-nucleus size, Avrami exponent, growth exponent, and crystallite size were calculated. Results show that the nucleation rate increases as the pressure increases. The change of critical-nucleation size is not obvious as the pressure increases. With the pressure increasing, growth exponent decreases, indicative of decreased grain-growth rate. It was also found that with the pressure increasing, the Avrami exponent decreases, indicating that the increased pressure has an effect on growth modes during solidification, which changes from three-dimensional growth to one-dimensional growth. Results of XRD simulation shows that with pressure increasing, crystallite size decreases. Full article

In this research, the numerical calculation for elastic and nonlinear strains of Fe metal and FeC alloy under different pressures has been performed by the statistical moment method SMM with Mie–-Lennard–Jones potential (MLJ) and Embedded-Jones potential Atom Method (EAM). The analysis reveals that an enhancement in the concentration (cC) from 0 to 5% causes a decrement in the Young’s modulus (E) at room temperature (T = 300 K) for FeC. These calculated results are consistent with the experimental results. In addition, the obtained stress-strain curves for Fe are in perfect agreement with the experimental curves. Besides, increasing the cC for a continuous strain decreases the stress, showing that adding C to Fe to form FeC steel will increase strength and hardness, but decrease elasticity and hardness. The results obtained will be very useful not only for experimental studies but also for theoretical studies of metals and their interstitial alloys. Full article

Molecular dynamics simulations of body-centered cubic (bcc) iron thin films with crack defects were carried out by adopting methods of EAM (Embedded Atom Method) potential, spin/exchange potential and spin/neel potential. In this article, the effects of the variation of distance between two crack defects and their directions on the magnetostrictive properties of the thin films are studied, and the corresponding microscopic mechanism is also analyzed. The results show that the defects affect the atomic magnetic moment nearby, and the magnetostrictive properties of thin iron films vary with the direction and spacing of the crack defects. If the defect spacing is constant, the iron model with crack perpendicular to the magnetization direction has stronger magnetostriction than that of parallel to the magnetization direction. The variation of the defect spacing has a great influence on the magnetostrictive properties of the iron model with crack direction parallel to magnetization direction, but it has a small effect on another perpendicular situation. The atoms between the defects may move, but if the defect spacing increases to a certain value, then none of the atoms will move. Full article

Understanding of the defect evolution mechanism under irradiation is very important for the research of pressure vessel steel embrittlement. In this paper, the embedded atom method (EAM) based canonical ensemble molecular dynamics (MD) method was used to study the evolution of the stacking structure of different nano-sized Cu_n (n = 13, 43 and 87) clusters in an Fe_bulk embedded with BCC lattice structure during continuous heating. The mean square displacement, pair distribution functions and atomic structures of Cu atom clusters at the nanometer scale were calculated at different temperatures. The structural changes present apparent differences, for the Fe_bulks contain nano-sized Cu clusters with different atom numbers during heating. For the Fe_bulk–Cu₁₃ system, since the ability to accommodate the atomic Cu in the Fe substrate is lesser, a small number of Cu atoms in BCC lattice positions cannot influence the whole structure of the Fe-Cu system. For the Fe_bulk–Cu₄₃ system, with an increase in temperature, a Cu atomic pile structural change happened, and the strain areas decreased significantly in the Fe_bulk, but a single strain area grew large. For the Fe_bulk–Cu₈₇ system, when the Cu atoms are constrained by the Fe atoms in bulk, only a few of the Cu atoms adjust their positions. With the increase in temperature, strain in the Fe eased. Full article

In the present study, molecular dynamics simulations were employed to investigate the effect of strain rate on the plastic deformation mechanism of nanocrystalline 316 L stainless-steel, wherein there was an average grain of 2.5–11.5 nm at room temperature. The results showed that the critical grain size was 7.7 nm. Below critical grain size, grain boundary activation was dominant (i.e., grain boundary sliding and grain rotation). Above critical grain size, dislocation activities were dominant. There was a slight effect that occurred during the plastic deformation mechanism transition from dislocation-based plasticity to grain boundaries, as a result of the stress rate on larger grain sizes. There was also a greater sensitive on the strain rate for smaller grain sizes than the larger grain sizes. We chose samples of 316 L nanocrystalline stainless-steel with mean grain sizes of 2.5, 4.1, and 9.9 nm. The values of strain rate sensitivity were 0.19, 0.22, and 0.14, respectively. These values indicated that small grain sizes in the plastic deformation mechanism, such as grain boundary sliding and grain boundary rotation, were sensitive to strain rates bigger than those of the larger grain sizes. We found that the stacking fault was formed by partial dislocation in all samples. These stacking faults were obstacles to partial dislocation emission in more sensitive stress rates. Additionally, the results showed that mechanical properties such as yield stress and flow stress increased by increasing the strain rate. Full article

The design of advanced nanostructured materials with predetermined physical properties requires knowledge of the relationship between these properties and the internal structure of the material at the nanoscale, as well as the dependence of the internal structure on the production (synthesis) parameters. This work is the first report of computer-aided analysis of high pressure consolidation (cold sintering) of bimetallic nanoparticles of two immiscible (Fe and Cu) metals using the embedded atom method (EAM). A detailed study of the effect of cold sintering parameters on the internal structure and properties of bulk Fe–Cu nanocomposites was conducted within the limitations of the numerical model. The variation of estimated density and bulk porosity as a function of Fe-to-Cu ratio and consolidation pressure was found in good agreement with the experimental data. For the first time, topological analysis using Minkowski functionals was applied to characterize the internal structure of a bimetallic nanocomposite. The dependence of topological invariants on input processing parameters was described for various components and structural phases. The model presented allows formalizing the relationship between the internal structure and properties of the studied nanocomposites. Based on the obtained topological invariants and Hadwiger’s theorem we propose a new tool for computer-aided design of bimetallic Fe–Cu nanocomposites. Full article

The adhesion feature of graphene on metal substrates is important in graphene synthesis, transfer and applications, as well as for graphene-reinforced metal matrix composites. We investigate the adhesion energy of graphene nanosheets (GNs) on iron substrate using molecular dynamic (MD) simulations. Two Fe–C potentials are examined as Lennard–Jones (LJ) pair potential and embedded-atom method (EAM) potential. For LJ potential, the adhesion energies of monolayer GN are 0.47, 0.62, 0.70 and 0.74 J/m² on the iron {110}, {111}, {112} and {100} surfaces, respectively, compared to the values of 26.83, 24.87, 25.13 and 25.01 J/m² from EAM potential. When the number of GN layers increases from one to three, the adhesion energy from EAM potential increases. Such a trend is not captured by LJ potential. The iron {110} surface is the most adhesive surface for monolayer, bilayer and trilayer GNs from EAM potential. The results suggest that the LJ potential describes a weak bond of Fe–C, opposed to a hybrid chemical and strong bond from EAM potential. The average vertical distances between monolayer GN and four iron surfaces are 2.0–2.2 Å from LJ potential and 1.3–1.4 Å from EAM potential. These separations are nearly unchanged with an increasing number of layers. The ABA-stacked GN is likely to form on lower-index {110} and {100} surfaces, while the ABC-stacked GN is preferred on higher-index {111} surface. Our insights of the graphene adhesion mechanics might be beneficial in graphene growing, surface engineering and enhancement of iron using graphene sheets. Full article

Most investigations dealing with fatigue crack propagation on the nanoscale, limit their studies on a loading scenario of constant stress or strain amplitudes. Since such a load scenario is rather rare, this paper aims to examine the influence of the load sequence on the crack growth using bcc iron. For this purpose, a specimen containing a central crack was loaded repeatedly by varying the load amplitude. All computations were carried out using molecular dynamics methods (MD), and the material behaviour was represented by utilising an embedded atom method (EAM) potential. Significant deviation in the crack growth behaviour was observed when loading the specimens with variable amplitudes rather than with constant amplitudes. Cracks did not only extend during the loading phase but also in the initial phase of the unloading process where cracks expanded from voids that had been formed in the last phase of loading. These voids coalesced with the main crack as the specimen was subjected to further loading. Full article