Sergiy V Divinski

University of Münster | WWU · Institute of Material Physics

Severe plastic deformation (SPD) is effective in producing bulk ultrafine-grained and nanostructured materials with large densities of lattice defects. This field, also known as NanoSPD, experienced a significant progress within the past two decades. Beside classic SPD methods such as high-pressure torsion, equal-channel angular pressing, accumulat...

Grain boundary (GB) solute diffusion of Ge in Cu polycrystals was systematically investigated by the radiotracer serial sectioning technique using 68Ge and 71Ge isotopes. The diffusion measurements were carried out under conditions of Harrison’s B- (923–626 K) and C- (576–451 K) type diffusion regimes. In the B-type diffusion regime, the triple pro...

Solute diffusion of Ag in polycrystalline γ-Fe-40 wt.% Ni alloy was studied by means of the radiotracer technique. For bulk and grain boundary diffusion, the following Arrhenius parameters were established: D v 0 = 1.2 × 10 − 3 m 2 / s $ D_v^0 = 1.2 \times {10^{ - 3}}{m^2}/s $ and Q v = 279 kJ/mol and P ⁰ = 8:1 ⨯ 10 –14 m ³ /s and Q gb = 126 kJ/mol...

Bulk and grain boundary (GB) diffusion of Nb in α-Fe were studied in the temperature interval from about 700 to 1100 K by the radiotracer method combined with serial sectioning. A non-Arrhenius temperature dependence of Nb bulk diffusion was established below the Curie temperature Tc. This observation was discussed in relation to the well-known mag...

We perform ab initio density-functional-theory (DFT) calculations to investigate the vacancy formation and migration energies in HCP Al-Hf-Sc-Ti-Zr high entropy alloys (HEAs) and their subsystems from binaries to quinaries. For the vacancy formation properties, we utilize the special quasi-random structure approach in conjunction with a statistical...

Tracer diffusion of the substitutional components in (CoCrFeNiMn)$_{1-x}$C$_x$ high-entropy alloys with x = 0.002, 0.005 and 0.008 (in at. fractions) is measured at elevated temperatures from 1173 to 1373 K. Two different characteristic effects of interstitial carbon addition on substitutional diffusion in these FCC alloys are distinguished. At the...

An accurate prediction of atomic diffusion in Fe alloys is challenging due to thermal magnetic excitations and magnetic transitions. We investigate the diffusion of Mn in bcc Fe using an effective interaction model and first-principles based spin-space averaged relaxations in magnetically disordered systems. The theoretical results are compared wit...

Motivation Our earlier report indicates that the nanocomposite high entropy alloys (HEA) produced by high pressure torsion (HPT) after 15 revolutions comprises of three distinct phases. The initial FCC and BCC nanocrystalline phases as well as an amorphous phase which results from elevated stress accumulation and elemental migration into the BCC ph...

Tracer diffusion is one of most reliable techniques for providing basic kinetic data in solids. In the present review, selected direct methods, in particular the radiotracer measurements as a superior technique due to its high sensitivity, Secondary-Ion-Mass-Spectroscopy (SIMS) profiling, X-Ray Diffraction measurements and Rutherford Backscattering...

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 ar...

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 profile...

Differential scanning calorimetry measurements on different bulk metallic glasses show no measurable rejuvenation upon deeply cooled (cryogenic) thermal cycling. This applies both to as-quenched and well-annealed samples. Extensive molecular dynamics simulations of a generic model glass former corroborate these observations. We disentangle the effe...

The impact of thermo-mechanical treatment, in particular of room temperature high-pressure torsion (HPT), cold rolling and cryogenic thermo-cycling on shear band diffusion in a model Pd40Ni40P20 bulk metallic glass is investigated. Tracer diffusion measurements reveal the existence of fast short-circuit diffusion in deformed glasses and the diffusi...

The recently proposed pair-exchange diffusion model for multicomponent diffusion in a random alloy is analyzed in detail. The model defines the differences of chemical potential gradients of two elements as general driving forces for interdiffusion and the corresponding proportionality coefficients as pair-mobilities for atomic exchange fluxes of a...

A nanolaminated surface layer was produced on interstitial-free steel by surface mechanical rolling treatment. While the microstructure showed relatively high thermal stability during annealing at 500°C, significant grain boundary (GB) migration occurred in the nanolaminated surface layer during chromizing at the same temperature. GB diffusion of C...

High-pressure torsion was applied to join two disks of single-phase equiatomic fcc CoCrFeMnNi and bcc HfNbTaTiZr high entropy alloys (HEAs). After 15 revolutions a bulk nanocomposite had developed with alternating nano-lamellae of elongated nanocrystalline CoCrFeMnNi and mixed amorphous-nanocrystalline HfNbTaTiZr, exhibiting complex microstructures...

A single Cr-rich σ-phase alloy with a composition of Co17Cr46Fe16.3Mn15.2Ni5.5 (at.%) and a tetragonal lattice structure was produced. The tracer diffusion coefficients of Ni and Fe were measured by secondary ion mass spectroscopy using the highly enriched ⁶⁴Ni and ⁵⁸Fe natural isotopes. On the homologous temperature scale, Ni and Fe diffuse in the...

Tracer diffusion of the matrix elements in CoCrFeNiMn-based high-entropy alloys with 0.2, 0.5 and 0.8 at.% carbon is measured at 1373 K. The diffusion coefficients are found to depend non-monotonously on the carbon content. The diffusion retardation in low-C alloys is discussed in terms of the impact of interstitially-dissolved carbon on the vacanc...

For the first time, multicomponent alloys belonging to a B2-ordered single phase were designed and fabricated by melting route. The design concept of high entropy alloys is applied to engineering the transition metal sublattice of binary B2 aluminide. The equiatomic substitution of transition metal elements in the Ni sublattice of binary AlNi follo...

The impact of severe plastic deformation by high-pressure torsion on the relaxation of the glassy and supercooled liquid states of Pd 40Ni 40P 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 an...

A novel tracer-interdiffusion couple technique is utilized to measure the concentration-dependent tracer-(59 Fe) diffusion coefficients in the B2-ordered Al 50 (Ni,Fe) 50 alloys at 1373 K in a single experiment. The influence of variable molar volume on the diffusion coefficients is examined. The tracer diffusion coefficients determined under chemi...

Tracer-diffusion of constituting elements in single-crystalline CoCrFeNi and CoCrFeMnNi is measured from 923 K to 1373 K. In CoCrFeMnNi, low-temperature deviations from otherwise linear Arrhenius-type dependencies are seen for all elements excluding Mn. The kinks are prominent at about 1100 K for Co and Ni and at 900 K for Cr and Fe indicating the...

The problem of estimation of the tracer diffusion coefficients is solved by utilizing a novel tracer-interdiffusion couple technique even in the absence suitable radioisotope of one of the components and absence of reliable thermodynamic parameters. This is demonstrated by generating reliable and reproducible mobility data in the alloys of the Fe-G...

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 def...

The microstructures and phase compositions of Fe–Ga alloys with Ga contents from 15 to 45 at.% are investigated in detail applying prolonged annealing treatments at temperatures below 600 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating-sample magnetometry (VSM), and Electron backscatter diffraction (EBSD) coupled with...

We employed the thermal grooving method and determined the ratio of grain boundary and surface energies in ultrafine grain Ni produced by high pressure torsion. The average values of the relative grain boundary energies were 0.41 and 0.35 after the primary recrystallization at 500°C, and after equilibrating annealing at 800°C, respectively. A signi...

Grain boundaries of metallic materials subjected to severe plastic deformation exhibit significantly enhanced diffusivity and excess energy compared with their relaxed poly- or bi-crystalline counterparts even when the macroscopic degrees of freedom are the same in both types of grain boundaries. Boundaries of excess energy are/can be relaxed by an...

Grain boundary structure-property relationship was studied in a Ni-base 602CA coarse-grained alloy using a novel correlative tracer diffusion-analytical microscopy approach. Co-existence of several short-circuit contributions to tracer diffusion was distinguished at higher temperatures. These contributions were related to different families of high...

Additively manufactured (AM) metallic materials contain typically numerous grown-in defects which limit durability and mechanical properties of workpieces. However, the existence and impact of non-equilibrium vacancies and dislocations and especially the state of grain boundaries in AM materials remained completely unexplored. Here we are presentin...

An experimental-ab initio approach is applied to investigate solute diffusion in hexagonal high-entropy alloys. The radioisotope ⁵⁷Co is selected to probe the diffusion behaviour in a series of HCP alloys, from equiatomic binary (HfZr) and ternary (HfTiZr) to quinary Al5Sc20Hf25Ti25Zr25 at.% and Al15Sc10Hf25Ti25Zr25 at.% high-entropy alloys. Diffus...

For applications, metallic glasses need to retain their high strength over enhanced strain ranges. However, many metallic glasses show catastrophic failure, even in or close to the end of the regime that conventionally has been thought to be elastic. Recent observations of irreversible events at low strains shed some doubt on this nomenclature. In...

Composition-dependent diffusion coefficients are determined in B2-Ni(CoPt)Al system following the pseudo-binary and pseudo-ternary methods, which would not be possible otherwise in a quaternary inhomogeneous material fulfilling the equations developed based on the Onsager formalism. The pseudo-binary interdiffusion coefficients of Ni and Al decreas...

Grain boundary diffusion of the principal elements ⁵⁷Co, ⁵¹Cr, ⁵⁹Fe and ⁵⁴Mn in a coarse-grained equiatomic 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 th...

Tracer diffusion of all constituting elements is studied at various temperatures in a series of (CoCrFeMn)100−xNix 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...

Short-circuit diffusion in fine-grained Ni samples processed by Spark Plasma sintering has been investigated by the radiotracer technique. Ni grain boundary self-diffusion is measured in samples sintered from commercial as-received powder and from a powder processed by mechanical milling (MM). Both samples displayed high penetration of the radiotra...

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,...

The influence of Co micro-alloying (1 at. %) on the shear band diffusion and the relaxation processes in a model PdNiP bulk metallic glass is investigated. The shear bands are induced by one-pass cold-rolling. In addition to a fast shear band diffusion branch (Dsb≃10−16m2/s at 473 K), with the diffusivity being similar to that observed for the cold...

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 pur...

Grain boundary tracer diffusion of Ni, Fe and Cr was studied in a Ni-base 602CA coarse-grained alloy. A co-existence of several short-circuit contributions was distinguished at higher temperatures in Harrison's B-type regime (773-873 K), which were related to different families of high-angle grain boundaries with distinct coverages by precipitates...

An experimental study is performed of the effect constant and pulsed magnetic fields have on the coefficient of diffusion for Sn in α-Fe in the 39.8–557.2 kА m⁻¹ range of magnetic field intensities and 1‒21 Hz range of frequencies at 730°С. It is found that the pulsed magnetic fields have a considerable effect on the coefficient of diffusion for Sn...

Self-diffusion in ordered pseudo-binary multicomponent aluminides is investigated. Equiatomic substitution of transition metal sublattice in aluminides is performed to produce multicomponent alloys Al(CoNi), Al(FeNi), Al(CoFe), Al(CoFeNi), Al(CoFeMnNi) and Al(CoCuFeMnNi). X-ray diffraction and electron microscopy confirm the presence of single phas...

Euromat 2019, Section A5, 4 September 11:30 am

You can download our paper on editor's site (during 50 days only since 03-09-2019) by clicking on the link: https://authors.elsevier.com/c/1ZgNM3IWkbyXAP Best regards JG Gasser

The present knowledge on grain boundary-related phenomena specific for severely plastically deformed materials is reviewed and critically analyzed in detail. Severe plastic deformation is shown to introduce specific metastable states of the grain boundaries which are characterized by enhanced diffusion rates, high-density of specific structure elem...

The alloying of Ti with Cu(Sn) and Nb significantly increases the grain boundary diffusion-controlled growth kinetics of Nb3Sn accompanied with a decrease in the activation energy in the Cu(5.5 at.% Sn, Ti)/Nb and Cu(5.5 at.% Sn)/Nb(Ti) diffusion couples. In either case, the β-(Ti,Nb) precipitates form at the grain boundaries of Nb3Sn. On the other...

The impact of Co micro-alloying on low temperature specific heat capacity and the relaxation processes in a model Pd 40Ni 40P 20 bulk metallic glass in both as-cast and cold-rolled states was investigated. In addition to an excess (Boson) peak at low temperatures of about 12 to 14 K, a magnetic heat capacity anomaly in the Co alloyed glass below 10...

Grain boundary diffusion of iron in high purity polycrystalline copper is measured using the radiotracer technique and applying the ⁵⁹Fe isotope. At lower temperatures, T<949 K, the measurements are performed under Harrison's C-type kinetic regime and the grain boundary diffusion coefficient of Fe in Cu, Dgb, is determined, Dgb=5.6⋅10⁻⁶×exp(−121kJm...

The diffusion kinetics in a CoCrFeMnNi high entropy alloy is investigated by a combined radiotracer–interdiffusion experiment applied to a pseudo-binary Co15Cr20Fe20Mn20Ni25/Co25Cr20Fe20Mn20Ni15 couple. As a result, the composition-dependent tracer diffusion coefficients of Co, Cr, Fe and Mn are determined. The elements are characterized by signifi...

The diffusion kinetics in a CoCrFeMnNi high entropy alloy is investigated by a combined radiotracer--interdiffusion experiment applied to a pseudo-binary Co$_{15}$Cr$_{20}$Fe$_{20}$Mn$_{20}$Ni$_{25}$ / Co$_{25}$Cr$_{20}$Fe$_{20}$Mn$_{20}$Ni$_{15}$ couple. As a result, the composition-dependent tracer diffusion coefficients of Co, Cr, Fe and Mn are...

The diffusion kinetics in a CoCrFeMnNi high entropy alloy is investigated by a combined radiotracer-interdiffusion experiment applied to a pseudo-Ni 15 couple. As a result, the composition-dependent tracer diffusion coefficients of Co, Cr, Fe and Mn are determined. The elements are characterized by significantly different diffusion rates, with Mn b...

Tracer diffusion of Co, Cr, Fe and Ni is measured at 1373 K in Co20Cr20Fe20Mn20Ni20, Co10Cr10Fe10Mn10Ni60 and Co2Cr2Fe2Mn2Ni92 alloys. Diffusion retardation in the high-entropy Co20Cr20Fe20Mn20Ni20 alloy is most prominent in comparison to the Co2Cr2Fe2Mn2Ni92 solid solution, however the concept of ‘sluggish’ diffusion cannot be used as a blanket st...

The present work provides a first experimental assessment of the product of thermodynamic factor (Φ) and the cross correlation term (S) for high entropy alloys. Following a pseudo-binary approach, the concentration-dependent interdiffusion coefficients are determined for CoCrFeNi and CoCrFeMnNi high-entropy alloys at 1423 K using four different dif...

The formation of precipitates in metallic alloys is determined by a two-way chemomechanical coupling. While the dependence on solute diffusion is apparent, the opposite effect, namely the impact of nanoprecipitates on the diffusion, is highlighted in the present paper. Using severe plastic deformation and post-deformation annealing of an Al-based a...

High entropy alloys are multicomponent alloys, which consist of five or more elements in equiatomic or nearly equiatomic concentrations. These materials are hypothesized to show significantly decreased self-diffusivities. For the first time, diffusion of all constituent elements in equiatomic CoCrFeNi and CoCrFeMnNi single crystals and additionally...

Grain boundary self-diffusion of titanium in nanocrystalline TiO2 films is investigated in an extended temperature interval by the radiotracer technique applying the ⁴⁴Ti isotope. The diffusion annealing treatments are performed at low and high oxygen partial pressures. At low oxygen partial pressure Ti grain boundary self-diffusion follows an Arrh...

The dependence of magnetostriction and magnetic properties in Fe-19Ga-xTb (x = 0–0.37 at. %) and Fe-27.4Ga-xTb (x = 0–0.5 at. %) alloys on the concentration of Tb has been analyzed. A phase enriched in Ga and Tb (up to 7 at. % Tb and 41 at. % Ga) was observed at the grain boundaries and inside the interdendritic regions after direct solidification....

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 fir...

The main principles of grain boundary engineering of an ultrafine-grained microstructure are studied via a systematic variation of the stacking fault energy (í µí»¾ í µí±†í µí°¹í µí°¸)µí°¸), solid solution effects (SSEs) and the homologous deformation/annealing temperatures choosing the Cu-Ni system as a model case for non-segregating alloys. Cu an...

Formation of microstructure in Ni under equal-channel angular pressing (ECAP) and dynamic channel-angular pressing (DCAP), its thermal stability and diffusion properties of grain boundaries are investigated. Grain boundary diffusion in the ultrafine-grained Ni is found to be significantly faster than in the coarse-grained Ni, which indicates a 'non...

The impact of a pulsed magnetic field on Sn diffusion in α-Fe is investigated within the magnetic field intensity range of 79.6–398.0 kА/m and the frequency range of 1–21 Hz at 730, 740, and 750 °С. The solute diffusion coefficients were measured by X-ray diffraction analysis. The pulsed magnetic field was found to influence significantly the diffu...

Impact of a constant magnetic field on decomposition of supersaturated solid solution is investigated for the system Cu-Be-Ni. A technical bronze Cu-1.9Be-0.3Ni (in wt.%) was water-quenched after holding at 800°C (0.5 h) and subsequently heat treated at 325°C, 350°C and 400°C for 1 hour without and with application of a constant magnetic field of 0...

A close comparison between the segregation data obtained by means of DFT-based calculations and diffusion experiments is provided using the grain boundary segregation of Ag, Au, Se, Ge, Ni, Co and Bi impurities in Cu as a case study. The density functional theory calculations along with the McLean segregation isotherm are applied to obtain the effe...

Grain boundary self-diffusion of titanium in nanocrystalline TiO 2 films is investigated in an extended temperature interval by the radiotracer technique applying the 44 Ti isotope. The diffusion annealing treatments are performed at low and high oxygen partial pressures. At low oxygen partial pressure Ti grain boundary self-diffusion follows an Ar...

Tracer diffusion in ordered intermetallic compounds is reviewed. The main attention is paid to aluminides of transition metals like Ni, Ti, and Fe. The available experimental data are analyzed with respect to crystalline lattice, point defects, and probable diffusion mechanisms. Effects of deviation from the stoichiometric composition and alloying...

The experimental methods of diffusion measurements are shortly reviewed. The tracer method is discussed in detail, together with its advantages and limitations. The main approaches to establish the underlying diffusion mechanism in a metallic material are presented.

Defects assist the diffusion process, whereas driving forces influence the rate of diffusion depending on the thermodynamics of alloying, diffusion mechanisms, diffusion paths, and defect production. Different types of diffusion are defined based on defects assisting the diffusion process and whether atomic transport occurs in the absence or presen...