This work is devoted to the development and comprehensive validation of a new interatomic potential for bcc and hcp refractory alloys based on the W-Mo-Nb-Ta-Zr-Ti system. The presented model allows the simulation of various structural transformations, as well as the behavior of crystal defects in several of the phases observed in this system. The classical form of the potential enables simulations of atomic systems comprising up to 108 atoms for durations longer than a million time steps using a routine computational setting. The wide applicability of the developed model is demonstrated by the example of studying phase transformations in Ti Nb alloys and the properties of defects in Laves phases.

The elastic properties of amorphous TiNiSn, a promising half-Heusler system for flexible and wearable devices, were investigated using experimental and theoretical methods. Nanoindentation measurements performed on amorphous TiNiSn thin film grown by magnetron sputtering yielded an elastic (Young's) modulus value of 132 GPa. To corroborate this result, density functional theory (DFT) calculations and two machine learning models were employed, where the latter were trained on available literature data. The DFT-derived elastic modulus of amorphous TiNiSn is 113 GPa (stress-free conditions), which is 15% lower than the experimental value. However, when hydrostatic stress is considered, arising from possible thermal loads and ion bombardment during thin film synthesis, the difference is reduced to 5%. Electronic structure analysis reveals that amorphous TiNiSn exhibits predominantly covalent bonding with a minor metallic contribution, which is consistent with the measured elastic modulus. Although both machine learning models underestimate the experimental modulus more than DFT, the theoretical results enhance understanding of the elastic behaviour of amorphous TiNiSn and highlight its potential for future applications in flexible microelectronic systems.

The aim of this study is to explore the internal damage mechanisms of AlSi12 metal matrix syntactic foam (MMSF) with embedded ceramic hollow spheres (CHSs) to understand the damage behavior during compressive loading. To achieve this goal, in situ synchrotron X-ray tomography is used. A qualitative and quantitative assessment of the initiation and gradual collapse of matrix, filler material, and pores is presented. The imaging-based investigation provided detailed visualization and tracking of failure mechanisms of the MMSF, with emphasis on the collapse of hollow spheres at the microstructural level. The structural parameters describing performance limits are experimentally determined and correlated with internal mechanisms. It is concluded that a homogeneous distribution of the second-phase filler material results in a sequential collapse in a localized region; this leads to controlled and predictable energy absorption. The CHSs rupture is found to be location dependent within the localized shear band region, with spheres of all diameters failing to a similar extent. The results from this work can be used to train or validate predictive models of MMSFs deformed under compressive loading conditions by correlating the 3D damage progression with the overall mechanical response.

The present study focuses on the computation of interfacial excess potential for the cohesive zones through which a brittle crack propagates in tungsten (W) twist grain boundaries (TGBs). Additionally, the influence of phosphorus (P) impurities is investigated. To this end, we have performed classical atomistic modeling of several ⟨110⟩ TGBs in their pristine and P-impurity segregated states. The modeling entails a mode-I stress intensity factor (𝐾_𝐼) controlled quasi-static loading setup, in which the cohesive zone is divided into small cohesive zone volume elements (CZVEs) that enable the measurement of the scale-independent interfacial excess energy potential associated with cleavage surfaces. The study shows that the cracks in all pristine TGBs exhibit brittle failure by advancing along the GB interface. The same fracture mechanism is also observed upon the introduction of P impurities. However, debris in the form of clustered W-P agglomerates is occasionally observed on the cleavage surfaces. As for the measured excess interface energy potential, it is independent of the height chosen for the CZVEs and their position relative to the initial crack tip. This makes it useful to quantify the P induced embrittlement of TGBs and for up-scaling the results for e.g. meso-scale continuum modeling. The presence of P impurities reduces the interfacial binding energy and the associated peak stress, which is an indication of GB embrittlement. These results are in line with the experimentally observed P induced GB embrittlement in W, previously reported in the literature.

The formation of the intermetallic 𝜎 phase (space group 𝑃⁢42/𝑚⁢𝑛⁢𝑚) has a detrimental effect on the ductility of transition-metal alloys. This theoretical study uses first-principles calculations to investigate the stability and thermodynamic properties of the WRe and WOs 𝜎 phases. Our study indicates that the 𝜎 phase becomes thermodynamically stable at its ideal composition for temperatures above 1050 K and 130 K for the WRe and WOs phases, respectively. We find that models that neglect the phonon contribution to the free energy may underestimate the amount of disorder in the 𝜎 phase at elevated temperatures. Furthermore, the 𝜎 phase becomes dynamically unstable for Re concentrations above 73 at.% Re and 53 at.% Os. For the WOs phase, the dynamic stability is sensitive to the lattice site occupation, and vibrations of the Os atoms are linked to the transformation into a dynamically stable orthorhombic phase.

Even after fifty years since its introduction, the empirical Thornton's structure zone diagram remains a valuable tool for predicting thin film microstructure. This diagram is essential for understanding the correlation between synthesis, composition, structure, and physical properties in emerging applications. In this work, we critically appraise this diagram by examining Sn─O thin films grown at room temperature using reactive magnetron sputtering. Based on transmission electron microscopy, Sn0.6O0.4 thin films form dendrites featuring nanosized Sn and SnO grains, rather than columns, which are not captured by the structure zone diagram. Using density functional theory and machine learning, we constructed a model to explain this unusual microstructure on the atomic scale. Kinetically limited surface diffusion yields SnO islands on Sn(001), which constitute the initial stage of dendrite formation. This study provides the potential to devise models for thin film microstructure evolution, enhancing performance in advanced applications, such as green energy generation and storage.

We present a new classical interatomic potential designed for simulation of the W-Mo-Nb system. The angular-dependent format of the potential allows for reproduction of many important properties of pure metals and complex concentrated alloys with good accuracy. Special attention during the development and validation of the potential was paid to the description of vacancies, screw dislocations and planar defects, as well as thermo-mechanical properties. Here, the applicability of the developed model is demonstrated by studying the temperature dependence of the elastic moduli and average atomic displacement in pure metals and concentrated alloys up to the melting point.

Zirconium hydride is commonly used for next-generation reactor designs due to its excellent hydrogen retention capacity at temperatures below 1000 K. These types of reactors operate at thermal neutron energies and require accurate representation of thermal scattering laws (TSLs) to optimize moderator performance and evaluate the safety indicators for reactor design. In this work, we present an atomic-scale representation of sub-stoichiometric ZrH_2−x (0.3≤𝑥≤0.6), which relies on ab initio molecular dynamics (AIMD) in tandem with velocity auto-correlation (VAC) analysis to generate phonon density of states (DOS) for TSL development. The novel NJOY+NCrystal tool, developed by the European Spallation Source community, was utilized to generate the TSL formulations in the A Compact ENDF (ACE) format for its utility in neutron transport software. First, stoichiometric zirconium hydride cross sections were benchmarked with experiments. Then sub-stoichiometric zirconium hydride TSLs were developed. Significant deviations were observed between the new δ-phase ZrH2−x TSLs and the TSLs in the current ENDF release. It was also observed that varying the hydrogen vacancy defect concentration and sites did not cause as significant a change in the TSLs (e.g., ZrH_1.4 vs. ZrH_1.7) as was caused by the lattice transformation from 𝜖- to δ-phase.

We investigate how the Re content affects the coefficient of thermal expansion (CTE) of the non-stoichiometric W-based  and  phases, forming upon neutron irradiation of W, to explore and quantify its mismatch between precipitates (W-Re) and matrix (W). To this end, we have conducted first-principles calculations using two approaches: the Debye-Grüneisen (DG) model and the quasi-harmonic approximation (QHA). The two approaches yield different results: the QHA, which is deemed to be the most accurate of the two, predicts substantial changes with Re content, while the acoustic-modes based DG model does not. The CTE of the σ and χ at stable Re contents is compared to experimental values for bcc-W and bcc-W-Re containing 25 at.% Re. Taking bcc-W as a reference, we find a significant mismatch in CTE of up to 37% and 62% for σ and χ, respectively, which may contribute to thermal stress buildup in the material at elevated temperatures. The mismatch is shown to increase with the temperature and Re content for both phases. The produced data are used to fit a temperature and Re concentration-dependent analytical function of the CTE for both phases, which can be employed as input for continuum mechanical modeling.Previous article in issue

Ni-based superalloys, essential for high-temperature applications, derive strength from coherent second-order precipitates that impede dislocation motion through coherency misfit and elastic mismatch. This study employs multi-component phase-field crystal (PFC) simulations to explore the elastic deformation of such precipitates. Using a binary ordered square structure for the precipitate and a single species square structure for the matrix, elastic properties and lattice parameters are fitted to data from ab initio density functional theory calculations for Ni and Ni3Ti systems. Simulations reveal a smooth strain gradient across the matrix-precipitate interface with coherency misfit influenced by precipitate size and strain state. These findings highlight the utility of PFC simulations for understanding strain distribution and deformation in precipitate-matrix systems with the potential to offer insights for both experimental and computational studies.