arXiv subjects

Sergiy V. Divinski

Publications and source records attributed to Sergiy V. Divinski.

15 recordsLinked to original sources

arXiv2026

Impact of interstitial carbon on local lattice distortions in CoCrFeMnNi high-entropy alloys

Here, we explore component-dependent local lattice distortions in polycrystalline, equiatomic, face-centered cubic CrMnFeCoNi high-entropy alloys and their modifications induced by dilute interstitial carbon. Multi-edge extended X-ray absorption fine structure spectroscopy combined with reverse Monte Carlo analysis reveals that the Cr component experiences the most substantial local distortions, independent of the temperature of prolonged annealing treatments (993 K or 1373 K) and the nominal carbon content (0 to 0.8 at.%). The static disorder around Cr atoms was found to increase markedly and monotonically upon carbon alloying, whereas Mn, Fe, Co, and Ni demonstrate weaker and non-monotonic tendencies. The carbon-induced lattice distortions extend over several coordination shells, indicating the pronounced effect of the carbon presence on the local environment around Cr absorbers. First-principles density functional theory and finite-temperature molecular dynamics simulations confirm the greater impact of carbon on the local lattice distortions around Cr than around the other $3d$ constituent elements, based on the previous finding that carbon preferentially occupies Cr-rich interstitial sites. These results provide decisive hints towards the atomistic origin of the non-monotonic diffusion behavior previously reported for carbon-doped CrMnFeCoNi alloys, and are noticeable for understanding the carbon-induced phase transitions in compositionally complex systems.

cond-mat.mtrl-sci↗

arXiv2025

Lattice distortions and non-sluggish diffusion in BCC refractory high entropy alloys

Refractory high-entropy alloys (RHEAs) have emerged as promising candidates for extreme high-temperature applications, for example, in next-generation turbines and nuclear reactors. In such applications, atomic diffusion critically governs essential properties including creep resistance and microstructural stability. The present study systematically investigates impurity diffusion of Co, Mn, and Zn in single phase (BCC solid solution) HfTiZrNbTa and HfTiZrNbV RHEAs applying the radiotracer technique. A neutron total scattering technique is used to evaluate the pair distribution functions and element-specific lattice distortions in these alloys. \textit{Ab initio}-based calculations give access to lattice distortions and solubilities of the impurities under investigation, including the impact of short-range order. The diffusion results are discussed in relation to calculated substitutional and interstitial solution energies, local lattice distortions, and short-range order effects. Co diffusion is found to be dominated by the interstitial mechanism, exhibiting fast diffusion. These findings reveal important structure-property relationships between local atomic environments and diffusion kinetics in BCC RHEAs, providing critical insights for designing alloys with enhanced high-temperature performance through targeted control of impurity diffusion processes.

cond-mat.mtrl-sci↗

arXiv2024

Sodium diffusion in alkali feldspars: Towards the impact of Al/Si ordering

Tracer diffusion of Na in natural alkali feldspars including sanidine, adularia and orthoclase with different Na:K ratios is measured using the radiotracer technique and applying the 22Na radioisotope. The tracer diffusion measurements along the crystallographic directions perpendicular to (001) and (010) in alularia feldspar reveled a slight (within a factor of two to three) anisotropy of Na diffusion with the faster diffusion rates along the perpendicular to (001) directions, while this difference was less prominent in orthoclase. The anisotropy of Na diffusion is specifically addressed for orthoclase and the full diffusion tensor is determined. The impact of temperature and composition on diffusion in natural alkali feldspars is discussed with respect to impurities and intrinsic defects. The state of Al/Si ordering is proposed to have a significant influence on the Na diffusion rates in alkali feldspars.

cond-mat.mtrl-sci↗

arXiv2024

Ab initio machine-learning unveils strong anharmonicity in non-Arrhenius self-diffusion of tungsten

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 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 the 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.

cond-mat.mtrl-sci↗

arXiv2021

Interface-Driven Thermo-Electric Switching Performance of VO$^+$ Diffused Soda-Lime Glass

Strongly confined NaVO$^+$ segregation and its thermo-responsive functionality at the interface between simple sputter-deposited amorphous vanadium oxide thin films and soda-lime glass was substantiated in the present study by in-situ temperature-controlled Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The obtained ToF-SIMS depth profiles provided unambiguous evidence for a reversible transformation that caused systematic switching of the NaVO$^+$/ Na$^+$ and Na$^+$/ VO$^+$ intensities upon cycling the temperature between 25 $^\circ$C and 340 $^\circ$C. Subsequently, NaVO complexes were found to be reversibly formed (at 300 $^\circ$C) in vanadium oxide diffused glass, leading to thermo-responsive electrical behaviour of the thin film glass system. This new segregation -- and diffusion-dependent multifunctionality of NaVO$^+$ -- points towards applications as an advanced material for thermo-optical switches, in smart windows or in thermal sensors.

physics.app-ph↗

arXiv2020

Impact of severe plastic deformation on the relaxation of glassy and supercooled liquid states of amorphous Pd$_{40}$Ni$_{40}$P$_{20}$

The impact of severe plastic deformation by high-pressure torsion on the relaxation of the glassy and supercooled liquid states of Pd$_{40}$Ni$_{40}$P$_{20}$ was investigated using a combination of differential scanning calorimetry, low-temperature heat capacity and fluctuation electron microscopy. The changes in the calorimetric signals due to deformation and subsequent heat treatments were analyzed and a correlation between deformation (rejuvenation) and annealing (relaxation) was found in relation to medium-range order (MRO). Moreover, a coupling between the occurrence of an exothermic peak in the supercooled liquid state and specific changes in the MRO types were identified. These findings are comprehended in a potential energy landscape scheme offering a new approach for MRO engineering of glasses.

cond-mat.mtrl-sci↗

arXiv2020

Grain boundary diffusion in CoCrFeMnNi high entropy alloy: kinetic hints towards a phase decomposition

Grain boundary self-diffusion of $^{57}$Co, $^{51}$Cr, $^{59}$Fe and $^{54}$Mn in a coarse-grained, single-phase fcc CoCrFeMnNi high entropy alloy is measured in a wide temperature range of 643 to 1273~K in both C- and B-type kinetic regimes after Harrison's classification. The results suggest that the product of the pertinent segregation factors, $s$, and the grain boundary width, $δ$, is about 0.5~nm for all elements at temperatures $T>800$~K. Whereas one short-circuit contribution is observed at higher temperatures above 800~K, the penetration profiles in the C-type kinetic regime (643 -- 703~K) reveal two distinct contributions that hint towards a phase decomposition at a fraction of high-angle grain boundaries at these temperatures. A correlative microscopy combining transmission Kikuchi diffraction and atom probe tomography manifests formation of neighbouring Ni-Mn-rich and Cr-rich precipitates at a segment of high angle grain boundaries. Transmission electron microscopy revealed an increased dislocation density in the vicinity of such interfaces which is suggested to be a reason of the enhanced diffusion rates at low temperatures for such short circuits.

cond-mat.mtrl-sci↗

arXiv2020

Experimental and theoretical study of tracer diffusion in a series of (CoCrFeMn)$_{100-x}$Ni$_x$ alloys

Tracer diffusion of all constituting elements is studied at various temperatures in a series of (CoCrFeMn)$_{100-x}$Ni$_x$ alloys with compositions ranging from pure Ni to the equiatomic CoCrFeMnNi high-entropy alloy. At a given homologous temperature, the measured tracer diffusion coefficients change non-monotonically along the transition from pure Ni to the concentrated alloys and finally to the equiatomic CoCrFeMnNi alloy. This is explained by atomistic Monte-Carlo simulations based on a modified embedded-atom potentials, which reveal that local heterogeneities of the atomic configurations around a vacancy cause correlation effects and induce significant deviations from predictions of the random alloy model.

cond-mat.mtrl-sci↗

arXiv2018

A mystery of "sluggish diffusion" in high-entropy alloys: the truth or a myth?

High entropy alloys (HEAs) are considered as a novel class of materials with a large number of components available in nearly equatomic proportions. One of the characteristic properties of HEAs was believed to be so-called "sluggish" diffusion. The faith on this myth instead of rigorous experimental analysis played such a dominant role that the first set of data on interdiffusion, in fact based on an improper analysis, were cited in hundreds of articles to state the presence of sluggishness of diffusion rates in high entropy alloys. In this review, the recent data on atomic diffusion in HEAs are critically discussed. The discussion is focused on tracer diffusion which is already measured dominantly for polycrystalline, but in some cases for single crystalline high-entropy alloys. Alternatively, a rigorous analysis of the interdiffuson experiments, which provide the diffusion rates of chemical species, too, becomes more and more sophisticated for three and more elements in an alloy and it is challenging to derive physically sound quantities from a general multicomponent diffusion experiment. Most promising in this case is the diffusion couple technique, especially the so-called pseudo-binary approach. This approach is analyzed with a focus on the applicability and the possible errors induced if up-hill diffusion appears. It is shown that atomic diffusion in HEAs cannot a priori be considered as sluggish and both atomic interactions as well as correlation effects are responsible for the observed trends. Even if estimated on the same homologous scale, the diffusion retardation induced by a "high entropy" in FCC crystals is not simply proportional to the number of alloying components and it is shown to be similar to that induced by the L12 ordering in a binary system. Furthermore, the importance of cross-correlations in diffusion of different species in HEAs is highlighted.

cond-mat.mtrl-sci↗

arXiv2017

On the analysis of composition profiles in binary diffusion couples: systems with a strong compositional dependence of the interdiffusion coefficient

Diffusion couple technique is an efficient tool for the estimating the chemical diffusion coefficients. Typical experimental uncertainties of the composition profile measurements complicate a correct determination of the interdiffusion coefficients via the standard Boltzmann-Matano, Sauer-Freise or the den Broeder methods, especially for systems with a strong compositional dependence of the interdiffusion coefficient. A new approach for reliable fitting of the experimental profiles with an improved behavior at both ends of the diffusion couple is proposed and tested against the experimental data on chemical diffusion in the system Fe-Ga

cond-mat.mtrl-sci↗

arXiv2017

Grain boundary diffusion in severely deformed Al-based alloy

Grain boundary diffusion in severely deformed Al-based AA5024 alloy is investigated. Different states are prepared by combination of equal channel angular processing and heat treatments, with the radioisotope $^{57}$Co being employed as a sensitive probe of a given grain boundary state. Its diffusion rates near room temperature (320~K) are utilized to quantify the effects of severe plastic deformation and a presumed formation of a previously reported deformation-modified state of grain boundaries, solute segregation at the interfaces, increased dislocation content after deformation and of the precipitation behavior on the transport phenomena along grain boundaries. The dominant effect of nano-sized Al$_3$Sc-based precipitates is evaluated using density functional theory and the Eshelby model for the determination of elastic stresses around the precipitates.

cond-mat.mtrl-sci↗

arXiv2017

Low temperature features in the heat capacity of unary metals and intermetallics for the example of bulk aluminum and Al$_3$Sc

We explore the competition and coupling of vibrational and electronic contributions to the heat capacity of Al and Al$_3$Sc at temperatures below 50 K combining experimental calorimetry with highly converged finite temperature density functional theory calculations. We find that semilocal exchange correlation functionals accurately describe the rich feature set observed for these temperatures, including electron-phonon coupling. Using different representations of the heat capacity, we are therefore able to identify and explain deviations from the Debye behaviour in the low-temperature limit and in the temperature regime 30 - 50 K as well as the reduction of these features due to the addition of Sc.

cond-mat.mtrl-sci↗

arXiv2015

Combined volumetric, energetic and microstructural defect analysis of ECAP-processed nickel

Difference dilatometry and differential scanning calorimetry (DSC) are used to investigate defect annealing in ultrafine grained nickel processed by equal channel angular pressing (ECAP) at various temperatures. Different defect types and processes such as vacancies, dislocations, grain boundaries and grain-boundary relaxation can be detected. They can be distinguished due to their distinct kinetics as revealed by the release of excess volume and excess heat during linear heating. The data are quantified in combination with a detailed characterization of the microstructure. Values for the absolute vacancy concentration, the dislocation density, the grain boundary expansion and the excess of grain boundary expansion in ECAP-processed nickel are derived.

cond-mat.mtrl-sci↗

arXiv2013

Ultrafast atomic transport in recrystallizing ultrafine grained Ni

We studied tracer self-diffusion in ultrafine grained Ni prepared by high pressure torsion. Two Ni materials of low (99.6 wt. %) and high (99.99 wt. %) purity levels were investigated. While the ultrafine grained structure of less pure Ni remained stable during diffusion annealing, recrystallization and subsequent grain growth occurred in high purity Ni at the same annealing conditions. Nevertheless, qualitatively similar ultrafast diffusion rates were measured in the samples of both purity levels. In high purity Ni, the kinetics of recrystallization was found to deviate strongly from the predictions of the Johnson-Mehl-Avrami-Kolmogorov theory. Moreover, the ultrafast diffusion paths withstood the recrystallization process. A model which accounts for solute redistribution in front of the moving boundary is suggested. Retaining of deformation-induced ultrafast diffusion paths in recrystallized Ni is explained by a specific mechanism of enhanced stability of the residual ultrafine grained fraction against recrystallization.

cond-mat.mtrl-sci↗

arXiv2013

Effect of recrystallization on diffusion in ultrafine grained Ni

We studied the effect of recrystallization and grain growth on grain boundary self-diffusion in ultrafine grained Ni prepared by high pressure torsion. Two Ni materials of low (99.6 wt. %) and high (99.99 wt. %) purity levels were compared and the kinetic properties of stationary and mobile grain boundaries were examined in detail. Unusual concentration profiles with characteristic 'kinks' were measured for Ni self-diffusion in 99.99 wt. % pure Ni, which is undergoing recrystallization and grain growth during diffusion annealing treatment. This behavior is found to be related to specific kinetic properties of grain boundaries which encompass the recrystallized areas and consume numerous defects of the ultrafine grained matrix during their motion. We proposed a model of self-diffusion in recrystallizing material which takes into account a hierarchy of stationary and moving fast diffusion paths, and satisfactory explains the observed diffusion behavior.

cond-mat.mtrl-sci↗