Browsing by Author "Divinski, Sergiy V."

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Open Access
Ab initio machine-learning unveils strong anharmonicity in non-Arrhenius self-diffusion of tungsten
(2025) Zhang, Xi; Divinski, Sergiy V.; Grabowski, Blazej
The knowledge of diffusion mechanisms in materials is crucial for predicting their high-temperature performance and stability, yet accurately capturing the underlying physics like thermal effects remains challenging. In particular, the origin of the experimentally observed non-Arrhenius diffusion behavior has remained elusive, largely due to the lack of effective computational tools. Here we propose an efficient ab initio framework to compute the Gibbs energy of the transition state in vacancy-mediated diffusion including the relevant thermal excitations at the density-functional-theory level. With the aid of a bespoke machine-learning interatomic potential, the temperature-dependent vacancy formation and migration Gibbs energies of the prototype system body-centered cubic (BCC) tungsten are shown to be strongly affected by anharmonicity. This finding explains the physical origin of the experimentally observed non-Arrhenius behavior of tungsten self-diffusion. A remarkable agreement between the calculated and experimental temperature-dependent self-diffusivity and, in particular, its curvature is revealed. The proposed computational framework is robust and broadly applicable, as evidenced by first tests for a hexagonal close-packed (HCP) multicomponent high-entropy alloy. The successful applications underscore the attainability of an accurate ab initio diffusion database.
Open Access
A combined experimental and first-principles based assessment of finite-temperature thermodynamic properties of intermetallic Al3Sc
(2021) Gupta, Ankit; Tas, Bengü; Korbmacher, Dominique; Dutta, Biswanath; Neitzel, Yulia; Grabowski, Blazej; Hickel, Tilmann; Esin, Vladimir; Divinski, Sergiy V.; Wilde, Gerhard; Neugebauer, Jörg
We present a first-principles assessment of the finite-temperature thermodynamic properties of the intermetallic Al3Sc phase including the complete spectrum of excitations and compare the theoretical findings with our dilatometric and calorimetric measurements. While significant electronic contributions to the heat capacity and thermal expansion are observed near the melting temperature, anharmonic contributions, and electron–phonon coupling effects are found to be relatively small. On the one hand, these accurate methods are used to demonstrate shortcomings of empirical predictions of phase stabilities such as the Neumann–Kopp rule. On the other hand, their combination with elasticity theory was found to provide an upper limit for the size of Al3Sc nanoprecipitates needed to maintain coherency with the host matrix. The chemo-mechanical coupling being responsible for the coherency loss of strengthening precipitates is revealed by a combination of state-of-the-art simulations and dedicated experiments. These findings can be exploited to fine-tune the microstructure of Al-Sc-based alloys to approach optimum mechanical properties
Open Access
Interstitials in compositionally complex alloys
(2023) Baker, Ian; Grabowski, Blazej; Divinski, Sergiy V.; Zhang, Xi; Ikeda, Yuji
The effects of interstitial alloying on the mechanical and diffusive properties of compositionally complex alloys (CCAs), including high-entropy alloys (HEAs), are reviewed. The solubility of interstitial elements in CCAs can be extraordinarily high, a feature corroborated by ab initio density functional theory simulations. The yield stresses, work-hardening rates, and Hall-Petch slopes of CCAs are normally reported to increase due to interstitial alloying. In some CCAs, interstitial alloying has been found to enhance both strength and ductility, thus circumventing the traditional tradeoff between these properties. Self-diffusivities of the HEA CoCrFeMnNi are found to show complex dependences on interstitial C concentration as well as on temperature. Some CCAs with Laves phase or body-centered cubic crystal structures show potential as hydrogen-storage materials, with both experimental and computational research in this area steadily increasing. Based on the insights obtained, possible directions for further studies on the impacts of interstitial alloying in CCAs are suggested.