Segregation Energy Research Articles

Oxygen Evolution Catalysts with Iridium Oxide Supported on Doped Titanium Oxide: Role of Dopants on Catalysts Reactivity and Stability

Titanium dioxide (TiO2) is a semiconductor that has been extensively studied for its thermo and photo catalytic properties due to its high stability, abundant oxygen vacancies and low price. In electrochemistry, titanium dioxide has been used as support for anode catalysts in Proton Exchange Membrane Water Electrolysis (PEMWE). The electrolysis of water into oxygen and hydrogen is kinetically limited by the Oxygen Evolution Reaction (OER) occurring at the positive electrode with a four-electron transfer. The noble metal oxides of Ruthenium and Iridium are currently considered the best electrocatalysts for OER due to their high activity and relatively high IrO2 stability [1]. The high price and scarcity of these precious catalysts prompt a strong interest in minimizing their loading [2]. The use of an electronically conductive support allows to decrease the loading by increasing the surface to volume ratio of precious metal particles. Titania is highly stable at the high potentials used during the OER and can be made conductive using some transition metals as dopants [3].TiO2 exists in nature in three crystalline forms: rutile, anatase, and brookite but because iridium oxide is used for OER in its rutile phase, and to promote epitaxial growth, this work uses the doped-TiO2 rutile phase as a support for Iridium oxide catalysts.New synthetic routes based on sol-gel process are used to form (Ru, Nb, Ta)-TiO2 nanoparticles. The size, shape and crystalline structure of the support was controlled by tuning calcination temperature and the Ti precursor. The doped rutile TiO2 particles synthesized consist of an ideal support for iridium oxide nanoparticles deposited by wet impregnation in different loading and phase. The epitaxial growth from rutile TiO2 to rutile IrOx promotes the catalyst support interaction and electrical conductivity.All the catalysts were characterized by their physico-chemical and electrochemical properties towards the oxygen evolution reaction. The surface morphology and crystallinity of these materials was evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The activity toward oxygen evolution reaction was investigated in liquid electrolyte in a 3-electrode set-up. [1] Alia, S. M.; Rasimick, B.; Ngo, C.; Neyerlin, K. C.; Kocha, S. S.; Pylypenko, S.; Xu, H.; Pivovar, B. S. Activity and Durability of Iridium Nanoparticles in the Oxygen Evolution Reaction. J. Electrochem. Soc 163, 596-603 (2016) [2] Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D. A comprehensive review on PEM water electrolysis. Int. J. Hydrogen Energy 38, 4901– 4934 (2013) [3] Bauerfeind, K.C.L.; Laun, J., Frisch, M.; et al. Metal Substitution in Rutile TiO2: Segregation Energy and Conductivity. J. Electron. Mater. 51, 609–620 (2022)

Theoretical Investigation on the Stability of Second Phase Formation in Ba(Zr, M)O3-Δ By Electrode Derived Ni and Co Elements

Ba(Zr,M)O3-δ is a perovskite-type oxide in which B-site is partially substituted by the dopant element M. It is expected to be applied as a solid electrolyte in proton-conducting ceramic fuel cells (PCFC). In recent years, there has been concern that the diffusion of Ni from the anode and Co from the cathode e into the solid electrolyte causes second phase formation, resulting in cell degradation. For example, depending on the type and amount of dopant, highly resistive phase, BaM 2NiO5, is reported to be precipitated [1]. Thus, understanding the precipitation conditions and precipitation mechanism of the second phase is essential to control cell degradation. Our previous studies have shown that the energetic stability of the precipitates is dominant in the formation of the precipitates by the anode-derived Ni. On the other hand, concerning the formation of cathode-derived Co precipitates, a complex oxide considered to be spinel precipitates at the grain boundary.However, not enough research has been done, and there is a possibility of other compounds precipitating as well, depending on conditions.In the present study, we referred to our previous experimental evaluation and performed first-principles calculations to theoretically examine the precipitation of the second phase associated with the solid solution of Ni and Co in Ba(Zr,M)O3. Anode-derived Ni reacts with dopant element M to form precipitates, and the formation tendency was found to be organized by the ionic radius of the dopant element M. Co from the cathode is thought to segregate with Ni at the grain boundary of the solid electrolyte, and this mechanism was investigated in terms of segregation energy and solid solution energy of Ni in spinel at the grain boundary. Furthermore, the formation energies of complex oxides involving Co for various M elements were evaluated by first-principles calculations to investigate the relative stability of the oxides under various equilibrium conditions organized by chemical potentials. The results suggest that BaCoO3 is stable in an oxidation atmosphere, and this trend was most pronounced for M=Yb. It is thought that BaCoO3 precipitation does not deplete dopants from the solid electrolyte matrix phase and is not likely to lead to degradation. At the conference, the detailed precipitation mechanism and the changes in the lattice constants of BaZrO3 due to the solid solution of different elements with respect to chemical expansion will be discussed.AcknowledgmentThis research result was obtained as a result of the commissioned work (Development of Ultra-High Efficiency Protonic Ceramic Fuel Cell Devices WP2, WP3, JPNP20003) of the New Energy and Industrial Technology Development Organization (NEDO). We would like to express our gratitude to all parties involved.Reference[1] T. Kuroha, Y. Niina, M. Shudo, G. Sakai, N.Matsunaga, T. Goto, K. Yamauchi, Y. Mikami, and Y. Okuyama, Optimum dopant of barium zirconate electrolyte for manufacturing of protonic ceramic fuel cells, Journal of power sources, 506 (15), 230134 (2021).

Segregation at prior austenite grain boundaries: The competition between boron and hydrogen

The interaction between boron and hydrogen at grain boundaries has been investigated experimentally and numerically in boron-doped and boron-free martensitic steels using thermal desorption spectrometry (TDS) and ab initio calculations. The calculations show that boron and hydrogen are attracted to grain boundaries but boron can repel hydrogen. This behavior has also been observed using TDS measurements, with the disappearance of one peak when boron is incorporated into the microstructure. Additionally, the microstructure of both steels has been studied through electron backscattered diffraction, synchrotron X-ray measurements, and correlative transmission Kikuchi diffraction-atom probe tomography measurements. While they have a similar grain size, grain boundary distribution, and dislocation densities, pronounced boron segregation into PAGBs is observed for boron-doped steels. It indicates that boron in PAGBs is responsible for the disappearance of the TDS peaks for the boron-doped steel. Then, the equilibrium hydrogen concentration in different trapping sites has been evaluated using the Langmuir–McLean approximation. This thermodynamic model shows that the distribution of hydrogen is identical for all traps when the total hydrogen concentration is low for boron-free steel. However, when it increases, traps of the lowest segregation energies (mostly PAGBs) are firstly saturated, which promotes failure initiation at this defect type. This finding partially explains why PAGBs are the weakest microstructure feature when martensitic steels are exposed to hydrogen-containing environments.

Grain boundary self-diffusion and point defect interactions in α-U via molecular dynamics

Though metallic U-Zr fuel has been used in nuclear reactors since the 1960s, many of its fundamental and thermodynamic properties are still unknown. The α-U phase, which has a highly anisotropic crystal structure and physical properties, is present in U-Zr fuel. The character and behavior of α-U grain boundaries will strongly impact fuel thermophysical performance under irradiation. We study the interaction of point defects with grain boundaries, diffusion along grain boundaries, and the predicted diffusional creep behavior of α-U via molecular dynamics. We calculate the segregation energy of vacancies and interstitials to grain boundaries and quantify the biased sink strength of the grain boundaries, and observe that this sink strength is not strongly dependent on the grain boundary orientation. We also find that grain boundary diffusivity is strongly dependent on the grain boundary energy and grain boundary orientation. The presence of point defects within the grain boundary can induce diffusion in grain boundaries with low formation energies and can enhance diffusion in high-energy grain boundaries. We also find that diffusional creep of α-U at prototypical metallic fuel operation conditions is extremely high and could help explain observed metallic fuel swelling behaviors.

Grain boundary segregation spectrum in basal-textured Mg alloys: From solute decoration to structural transition

Mg alloys are promising lightweight structural materials due to their low density and excellent mechanical properties. However, their limited formability and ductility necessitate improvements in these properties, specifically through texture modification via grain boundary segregation. While significant efforts have been made, the segregation behavior in Mg polycrystals, particularly with basal texture, remains largely unexplored. In this study, we performed atomistic simulations to investigate grain boundary segregation in dilute and concentrated solid solution Mg–Al alloys. We computed the segregation energy spectrum of basal-textured Mg polycrystals, highlighting the contribution from specific grain boundary sites, such as junctions, and identified a newly discovered bimodal distribution which is distinct compared to the conventional skew-normal distribution found in randomly-oriented polycrystals. Using a hybrid molecular dynamics/Monte Carlo approach, we simulated segregation behavior at finite temperatures, identifying grain boundary structural transitions, particularly the varied fraction and morphology of topologically close-packed grain boundary phases when changing thermodynamic variables. The outcomes of this study offer crucial insights into basal-textured grain boundary segregation and phase formation, which can be extended to other relevant Mg alloys containing topologically close-packed intermetallics.

First-principles study of solute segregation and its effects on the cohesion of the Fe/Y2Ti2O7 interface in ferritic ODS alloy with He

The solute segregation and its effects on the cohesion of the Fe/Y₂Ti₂O₇ interface in ferritic oxide dispersion strengthened (ODS) alloy have been investigated using first-principles calculations. The computational results indicate that W, Cr, Al, Nb, Zr, and Hf are prone to segregate to the Fe/Y₂Ti₂O₇ interface and enhance the cohesive strength of the Fe/Y₂Ti₂O₇ interface, improving its stability. He atoms exhibit a strong tendency to segregate at the Fe/Y₂Ti₂O₇ interface, leading to embrittlement of the interface. Moreover, in the case of co-existing of W, Cr, Al, Nb, Zr, and Hf with He atoms, it is found that W, Cr, and Al increase the segregation energy of He at the Fe/Y₂Ti₂O₇ interface. This promotes the diffusion of He from the Fe/Y₂Ti₂O₇ interface into the bulk of the Y₂Ti₂O₇, thereby reducing He-induced embrittlement at the Fe/Y₂Ti₂O₇ interface. Finally, the electronic structures of the Fe/Y₂Ti₂O₇ interfaces with and without solute elements, as well as the interaction between metallic solutes and He, have been discussed in detail to reveal the mechanisms of alloying reduction effect on He-segregated embrittlement at the Fe/Y₂Ti₂O₇ interface. The results obtained from this work suggest that adjusting the alloying components in ODS alloys can improve the radiation resistance of the alloy, providing theoretical guidance for the design and optimization of ferritic ODS alloys.

A universal descriptor to determine the effect of solutes in segregation at grain boundaries

The control of solute segregation at grain boundaries is of significance in engineering alloy properties. However, there is currently a lack of a physics-informed predictive model for estimating solute segregation energies. Here we propose novel electronic descriptors for grain-boundary segregation based on the valence, electronegativity and size of solutes. By integrating the non-local coordination number of surfaces, we build a predictive analytic framework for evaluating the segregation energies across various solutes, grain-boundary structures, and segregation sites. This framework uncovers not only the coupling rule of solutes and matrices, but also the origin of solute-segregation determinants, which stems from the d- and sp-states hybridization in alloying. Our scheme establishes a novel picture for grain-boundary segregation and provides a useful tool for the design of advanced alloys.

An understanding of the segregation and migration mechanism of point defects in tungsten grain boundaries: An atomic scale simulation

In this study, molecular dynamics (MD) simulations are employed to investigate the interactions between point defects and grain boundaries (GBs) in tungsten. Firstly, the segregation energy of vacancies (Vs) and self-interstitial atoms (SIAs) to GBs is examined. The results indicate that both Vs and SIAs tend to segregate towards GBs. Notably, the different types of GBs exhibit varying attraction to Vs and SIAs. The interaction radius is applied to investigate the degree of segregation, which is a significant index of GBs’ attraction to Vs and SIAs. The segregation radius of SIAs is typically larger than that of Vs. High-angle grain boundaries (HAGBs) show strong segregation for SIAs, facilitating the aggregation at GBs. Additionally, elastic theory is applied to qualitatively discuss the factors influencing the segregation energy distribution. The differences in atomic free volume caused by hydrostatic stress and the lattice distortion induced by point defects lead to Vs and SIAs occupying different sites. Finally, the nudged elastic band (NEB) method is employed to study the migration of Vs and SIAs near GBs, revealing that migration energy barriers for Vs and SIAs in GBs are much lower than in bulk. GBs facilitate the migration of point defects. Low-angle grain boundaries (LAGBs) present a higher energy barrier for V migration. Vs tend to occupy the compressive region, while SIAs tend to occupy the tensile region. Particularly, in comparison to Vs, SIAs are more likely to segregate to GBs due to higher binding energy, wider interaction radius, and extremely lower diffusion energy barrier. This provides some insights into the segregation and migration of point defects in GBs.

High temperature stress relaxation behavior of high Si, Mo-doped austenitic stainless steels

The resistance to stress relaxation at high temperatures is of importance to fasteners. In this study, the stress relaxation behavior of high Si, Mo-doped austenitic stainless steels at 450, 510, 550, 600 and 650 °C were investigated, taking the microstructure evolution at high-temperature long-term condition into account. It is found that Mo can effectively mitigate the plastic strain rate at high temperatures by impeding the extension of partial dislocations, thus leading to a noteworthy enhancement in the stress relaxation resistance. The first-principles calculations indicated that the addition of Mo can suppress the formation of a multi-phase composed of G phase and ferrite at high temperatures, by increasing the segregation energy of Si, Cr, and Ni at grain boundaries. This multi-phase induces the formation of stacking faults and twins, and therefore is responsible for an abnormal reduction in the residual stress.

Learning grain boundary segregation behavior through fingerprinting complex atomic environments

Although continuum-scale segregation is a well-documented behavior in multi-species materials, detailed site-specific behavior remains largely unexplored. This is partially due to the complexity of analyzing materials at the requisite time and length scales for describing segregation with full atomic accuracy. Here, we better evaluate the segregation behavior of disordered grain boundary (GB) atomic environments through leveraging a set of Strain Functional Descriptors (SFDs) to generate an atomic descriptor (i.e., fingerprint). Using this atomic fingerprint, we resolve key relationships between atomic structure and segregation energy. Machine learning (ML) techniques are utilized in concert with this SFD fingerprint to elucidate complex relationships relating segregation potential to changes in specific features of the local Gaussian density captured by the SFDs. Finally, we identify relationships that indicate both individual and joint structure-property correlations. Linking atomic segregation energy to key structural features demonstrates the value of higher-order descriptors for uncovering complex structure-property relationships at an atomic scale.

First-principles study of the interaction of solutes with ∑3(11-1) symmetric tilt grain boundaries in α-Fe

Abstract The structural, cohesive and magnetic properties of a symmetric Σ3(70.53)[011](11-1) tilt grain boundary in pure bcc iron and with commonly used alloying elements (Si, Co, Mn, Ti, Cu, Mo, Nb, V, Cr and Ni) by means of density functional theory calculations are studied. Solubility and segregation energies were calculated for different positions of dissolved atoms. Calculations show a tendency for impurities to segregate near the boundary. It was found that the substituting Co, Cu and Ni in the layer adjacent to the boundary have an embrittling effect, while other atoms enhance the cohesion of the grains. Magnetic moments on GB atoms are significantly higher than those on bulk atoms.

Effect of alloying solutes on hydrogen segregation at pure iron Σ3(111) grain boundary: First-principles calculation

Hydrogen segregation behaviors at BCC-Fe Σ3 (111) grain boundary (GB) as well as the effects of alloying solutes were studied by the first-principles method. The segregation energy of alloying solutes at different periods presents a concave-down parabolic-like relationship with the atomic number, and the 4 d transition alloying solutes show a higher averaged segregation tendency. At the favorable trapping site, hydrogen segregation energy decreased by increasing the number of hydrogen atoms up to 0.85/Å2 in the plane vertical to the GB. Mo, Tc, Ru, Ta, W, Re, Os, and Ir strengthen GB and inhibit hydrogen segregation. Significantly, the interaction between alloying solutes and hydrogen segregation was elucidated by emphasizing the separation of the chemical and the mechanical contributions, and appropriate descriptors on hydrogen segregation energy influenced by alloying solutes were screened. This work offers theoretical backing to comprehend hydrogen segregation behaviors and the effects of alloying solutes to design advanced high-strength steels resistant to hydrogen embrittlement.

Solute Segregation and Pinning Effect on Lateral Twin Boundary in Magnesium

Deformation twinning creates a three-dimensional twin domain via the migration of forward, normal and lateral twin boundaries (TBs) with respect to twin shear direction, normal to twin plane and twin lateral direction. Solute segregation and pinning effect on the forward and normal TBs have been experimentally observed and demonstrated via atomistic simulations. Here, we conducted a comprehensive study of solute segregation and the pinning effect on the lateral TBs in Mg. First-principles density functional theory calculations were used to obtain the segregation and formation energies of 19 alloying elements in coherent regions of lateral TBs. Alloying elements with greater difference in atomic radius from Mg generally show more negative segregation energy. Moreover, alloying elements with good solubility are selected to demonstrate the pinning effect on a coherent interface. Ge, Ga, Y, Gd, La and Ca show negative segregation energy and solubility energy, indicating that these elements can form stable segregation and have a strong pinning effect at the lateral boundary. Molecular dynamics simulations revealed that solutes in coherent regions are more effective in pinning lateral TBs than those in misfit regions. The results provide insight into the selection of solute atoms for tailoring twinning behavior.

Investigating interfacial segregation of [formula omitted]/Al in Al–Cu alloys: A comprehensive study using density functional theory and machine learning

Solute segregation at the interface between the aluminum (Al) matrix and the Ω (Al2Cu) phase decreases the interfacial energy, impedes the coarsening of precipitates, and enhances the thermal stability of such precipitates. In this study, we employ density functional theory to systematically calculate solute segregation energies of 42 solute elements at the coherent and semi-coherent interfaces between the two phases, as well as mixing energies of these elements within the Al and Cu sublattices of the Ω phase. Using correlation analysis and machine learning methods, we establish the relationship between the solute segregation energy and 20 selected atomic descriptors. Metalloid and late transition metal elements are predicted as potential candidates for enhancing the thermal stability of Al–Cu alloys. We observe that the solute segregation energy at the interfacial site of the semi-coherent interface correlates with the atomic size of solute atoms and their solubilities within the Ω phase. The developed machine learning models exhibit the potential to predict solute segregation energies at various sites of the coherent and semi-coherent interfaces. Overall, our study provides valuable insights into the stabilizing potential of individual elements at the Ω/Al interface in Al–Cu alloys.

Point-Defect Segregation and Space-Charge Potentials at the Σ5(310)[001] Grain Boundary in Ceria

The atomistic structure and point-defect thermodynamics of the model Σ5(310)[001] grain boundary in CeO2 were explored with atomistic simulations. An interface with a double-diamond-shaped structural repeat unit was found to have the lowest energy. Segregation energies were calculated for oxygen vacancies, electron polarons, gadolinium and scandium acceptor cations, and tantalum donor cations. These energies deviate strongly from their bulk values over the same length scale, thus indicating a structural grain-boundary width of approximately 1.5 nm. However, an analysis revealed no unambiguous correlation between segregation energies and local structural descriptors, such as interatomic distance or coordination number. From the segregation energies, the grain-boundary space-charge potential in Gouy–Chapman and restricted-equilibrium regimes was calculated as a function of temperature for dilute solutions of (i) oxygen vacancies and acceptor cations and (ii) electron polarons and donor cations. For the latter, the space-charge potential is predicted to change from negative to positive in the restricted-equilibrium regime. For the former, the calculation of the space-charge potential from atomistic segregation energies is shown to require the inclusion of the segregation energies for acceptor cations. Nevertheless, the space-charge potential in the restricted-equilibrium regime can be described well with an empirical model employing a single effective oxygen-vacancy segregation energy.

Structural evolution and mechanical response of multiple Al Σ5(210) grain boundaries with segregation of solute atoms: First-principles study

Grain boundary (GB) segregation of solute atoms is a key factor affecting the microstructure and macroscopic properties of materials. In this study, first-principles calculations were carried out to investigate the effect of solute atoms (Mg and Cu) segregation on the structural evolution and mechanical response of Al ground-state Σ5(210) GB (GB-Ⅰ) and metastable Σ5(210) GBs (GB-Ⅱ and GB-Ⅲ). The GB energy, segregation energy, and the theoretical tensile strength of the multiple Σ5(210) GBs were calculated. The results show that both Mg and Cu atoms tend to segregate in the boundary plane, thus reducing GB energy and improving GB stability. The segregation of Cu atoms reduced the GB energy more significantly than that of Mg atoms. The segregation of solute atoms can change the symmetric GB structure into an asymmetric one or induce GB phase transformation. The theoretical strength of GB-I is weaker than that of the metastable GB-II with higher GB energy, suggesting that grain boundaries with higher energy are not necessarily unstable. In addition, the effect of solute atom segregation on the GB strength depends not only on the type of element but also on the specific GB structure. The weakening effect of Mg segregation in GB-I and GB-II is due to the weak MgAl bond which enlarges the low charge density region of GB and increases the free volume of GB. The strengthening of GB-I and GB-II by Cu segregation mainly depends on the stronger AlCu bond than AlAl bond along the GB fracture path. The enhanced strength of GB-III with Mg and Cu segregation is attributed to the GB structural phase transformation caused by the segregation of solute atoms. The calculation results further elucidate the relationship between element segregation and grain boundary characteristics.

Grain boundary segregation for the Fe-P system: Insights from atomistic modeling and Bayesian inference

In this work we re-assess experimental data for grain boundary (GB) segregation of P in bcc Fe with thermodynamic and statistical methods. The data are based on Auger-Electron-Spectroscopy (AES) measurements which have provided P GB concentrations for various bulk contents and temperatures for ferrite. While in the previous investigations of this system a single-site McLean equation was used to extract segregation enthalpy and entropy, we employ multi-site segregation models as suggested by atomistic simulations. We use a recently introduced methodology based on inter-atomic potentials to calculate the segregation energy spectrum, as well as vibrational entropy and solute-solute interactions of P in polycrystalline Fe, thereby obtaining a three-dimensional distribution of energy, entropy and interactions. Using this trivariate distribution we predict P GB concentrations and compare them to the experimental measurements. Furthermore, we calibrate the parameters of physical models of increasing complexity to the experimental data with an inverse modeling approach based on Bayesian inference. While it is not possible to seamlessly link the results from AES to atomistic modeling, our investigation provides significant new insights for thermodynamic modeling of GB segregation. The vibrational entropy deduced from experiment differs from physics based atomistic simulations even when taking the spectral nature of energy, entropy and interactions into account. However, the correlations of the quantities are in good agreement when considering the trivariate model. Our investigation highlights the need for new and more accurate experimental datasets of GB segregation.

The Effects on Stability and Electronic Structure of Si-Segregated θ′/Al Interface Systems in Al-Cu Alloys

This study systematically investigates the energy and electronic properties of Si-segregated θ′(Al2Cu)/Al semi-coherent and coherent interface systems in Al-Cu alloys using ab initio calculations. By evaluating the bonding strength at the interface, it has been revealed that Si segregated at the A1 site (Al slab) of the semi-coherent interface systems exhibits the most negative segregation energy, resulting in a noticeable decrease in total energy and an increase in interface adhesion. The electronic structure analysis indicates the presence of Al-Cu and Al-Al bonds, with Si occupying the A1 site. The strong bond formation between Al-Cu and Al-Al is essential for improving interface bonding strength. The results of the calculating analyses are consistent with the results of the previous experiments, and Si can be used as a synergistic element to reduce the θ′/Al interface energy and further reduce the coarsening drive of the θ′ precipitated phase, which can provide new perspectives and computational ideas for the compositional design of heat-resistant Al-Cu alloys.

First-principles modeling of corrosion current for passive magnesium alloys and its application in Mg-RE alloy

Theoretical calculation could simulate Mg alloy corrosion behavior from electrochemical thermodynamic factors. By considering the kinetic factor as the passivation oxide layer, a comprehensive corrosion current model has been set up in this work. The corrosion current modeling should belgJtot′=lgJa+∆lgJc+km×∑fm×∆Em+ki×∑(fi×∆Ei)−koxCPBR×Winterface−∆Gs−∆GF(ln10)RT)). The formula as koxCPBR×Winterface−∆Gs−∆GF(ln10)RT) is just for passivation factor. Alloying element segregation energy ∆Gs, oxide formation energy ∆GF, oxide PBR value CPBR, interface cleavage work Winterface have all been considered. By this more considerate modeling, the corrosion current lgJtot′ (related to polarization icorr) could be obtained for passivate Mg alloys such as Mg-RE series (RE =Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). Moreover, the prediction is quite coherent to experimental electrochemical polarization result. The work provides a more precisely prediction for Mg alloy with passivation. It also proposes a passivation criterion for seeking corrosion-resistant Mg alloy in another way.

A machine learning framework for the prediction of grain boundary segregation in chemically complex environments

The discovery of complex concentrated alloys (CCA) has unveiled materials with diverse atomic environments, prompting the exploration of solute segregation beyond dilute alloys. However, the vast number of possible elemental interactions means a computationally prohibitive number of simulations are needed for comprehensive segregation energy spectrum analysis. Data-driven methods offer promising solutions for overcoming such limitations for modeling segregation in such chemically complex environments (CCEs), and are employed in this study to understand segregation behavior of a refractory CCA, NbMoTaW. A flexible methodology is developed that uses composable computational modules, with different arrangements of these modules employed to obtain site availabilities at absolute zero and the corresponding density of states beyond the dilute limit, resulting in an extremely large dataset containing 10 million data points. The artificial neural network developed here can rely solely on descriptions of local atomic environments to predict behavior at the dilute limit with very small errors, while the addition of negative segregation instance classification allows any solute concentration from zero up to the equiatomic concentration for ternary or quaternary alloys to be modeled at room temperature. The machine learning model thus achieves a significant speed advantage over traditional atomistic simulations, being four orders of magnitude faster, while only experiencing a minimal reduction in accuracy. This efficiency presents a powerful tool for rapid microstructural and interfacial design in unseen domains. Scientifically, our approach reveals a transition in the segregation behavior of Mo from unfavorable in simple systems to favorable in complex environments. Additionally, increasing solute concentration was observed to cause anti-segregation sites to begin to fill, challenging conventional understanding and highlighting the complexity of segregation dynamics in CCEs.