Recent results on diffusion in nanostructured materials are reviewed. The analysis highlights the... more Recent results on diffusion in nanostructured materials are reviewed. The analysis highlights the importance of the proper account for a hierarchic microstructure which is often formed in nanostructured materials. The diffusion kinetics is such a material requires a special consideration in dependence on the temperature, diffusion time and the segregation level of the solute. Pressure-less sintering results in clustering of nanograins with significantly enhanced diffusivity of the inter-agglomerate boundaries. Severe plastic deformation produces a broad spectrum of high-angle grain boundaries (GBs) with different kinetic properties. The majority of the high-angle GBs reveals diffusivities very similar to those of general high-angle GBs in their well-annealed coarse-grained counterparts. Nevertheless, considerably faster short-circuit diffusion paths are detected, too. The origin, geometric arrangement, structural and kinetic properties of these high-diffusivity paths are comprehensively investigated and discussed.
2018-Sustainable Industrial Processing Summit, May 4, 2018
The presentation is focused on structure-property relationship for interfaces in severe plastical... more The presentation is focused on structure-property relationship for interfaces in severe plastically deformed (SPD) materials. The results are systematized for different types of SPD treatment, imposed strain, and induced defects, and the deformation parameters used (temperature, total strain and strain rate). The kinetic properties of interfaces in a broad spectrum of severe plastically deformed materials ranging pure metals to alloys, including the high-entropy alloys, are measured. A multi-level hierarchy of short-circuit diffusion paths is shown to be formed in ultrafine grained materials produced by SPD Treatment [1,2]. The key properties of deformation-modified grain boundaries, such as interface width, diffusion rate, free volume excess, are measured and analyzed in detail. A model of the deformation-modified grain boundary state is presented.
The ion-plasma deposition was used to produce intermetallic coatings on Al-based substrates. Stru... more The ion-plasma deposition was used to produce intermetallic coatings on Al-based substrates. Structure and properties of these coatings were investigated. It was found that a specific combination of nano-, quasi-, and amorphous intermetallic phases in coatings along with formation of extended transitional sublayer increases mechanical properties of the material. Simultaneously the higher adhesion can be obtained.
Tracer diffusion in ordered intermetallic compounds is reviewed. The main attention is paid to al... more 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 on diffusion in ordered intermetallic compounds are considered. Tracer diffusion in ternary alloys is illustrated for the system Ni–Fe–Al.
Abstract Composition-dependent diffusion coefficients are determined in B2-Ni(CoPt)Al system foll... more Abstract Composition-dependent diffusion coefficients are determined in B2-Ni(CoPt)Al system following the pseudo-binary and pseudo-ternary diffusion couple methods, which would not be possible otherwise in a quaternary inhomogeneous material fulfilling the conditions to solve the equations developed based on the Onsager formalism. The end-member compositions to produce ideal/near-ideal diffusion profiles are chosen based on thermodynamic details. The pseudo-binary interdiffusion coefficients of Ni and Al decrease in the presence of Co but increase in the presence of Pt. The pseudo-ternary interdiffusion coefficients indicate that the main interdiffusion coefficients increase significantly in the presence of Pt. Marginal changes of the cross interdiffusion coefficients substantiate a minor change of the diffusional interactions between the components. The thermodynamic driving forces show opposite trends with respect to composition as compared to the changes of the interdiffusion coefficients advocating a dominating role of the Pt(Co)-induced modifications of point defect concentrations. DFT-based calculations revealed that Pt alloying increases the Ni vacancy concentration and decreases the activation energy for the triple defect diffusion mechanism. These findings explain the increase in the thickness of the interdiffusion zone between the B2-Ni(Pt)Al bond coat and the single crystal superalloy Rene N5 because of Pt addition. Furthermore, the EPMA and TEM analyses reveal the growth of refractory elements-enriched precipitates.
Abstract The recently proposed pair-exchange diffusion model for multicomponent diffusion in a ra... more Abstract 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 pair of elements at the mesoscopic scale. The total fluxes of alloying elements are given as the sum over corresponding pair-contributions, which rely on a set of independent forces and maintain a meaningful symmetric form to satisfy Onsagers reciprocal relations. It is demonstrated that a consistent definition of interdiffusion coefficients requires the fulfillment of the Gibbs-Duhem relation by the applied thermodynamic Gibbs energy description. The expression for the marker velocity for multicomponent random alloy is derived in the pair-wise form as a sum of the differences of chemical potential gradients of two elements with the linear coefficients which are differences between corresponding mobilities. The application of the model to High Entropy Alloys is demonstrated.
Recent results on diffusion in nanostructured materials are reviewed. The analysis highlights the... more Recent results on diffusion in nanostructured materials are reviewed. The analysis highlights the importance of the proper account for a hierarchic microstructure which is often formed in nanostructured materials. The diffusion kinetics is such a material requires a special consideration in dependence on the temperature, diffusion time and the segregation level of the solute. Pressure-less sintering results in clustering of nanograins with significantly enhanced diffusivity of the inter-agglomerate boundaries. Severe plastic deformation produces a broad spectrum of high-angle grain boundaries (GBs) with different kinetic properties. The majority of the high-angle GBs reveals diffusivities very similar to those of general high-angle GBs in their well-annealed coarse-grained counterparts. Nevertheless, considerably faster short-circuit diffusion paths are detected, too. The origin, geometric arrangement, structural and kinetic properties of these high-diffusivity paths are comprehensively investigated and discussed.
2018-Sustainable Industrial Processing Summit, May 4, 2018
The presentation is focused on structure-property relationship for interfaces in severe plastical... more The presentation is focused on structure-property relationship for interfaces in severe plastically deformed (SPD) materials. The results are systematized for different types of SPD treatment, imposed strain, and induced defects, and the deformation parameters used (temperature, total strain and strain rate). The kinetic properties of interfaces in a broad spectrum of severe plastically deformed materials ranging pure metals to alloys, including the high-entropy alloys, are measured. A multi-level hierarchy of short-circuit diffusion paths is shown to be formed in ultrafine grained materials produced by SPD Treatment [1,2]. The key properties of deformation-modified grain boundaries, such as interface width, diffusion rate, free volume excess, are measured and analyzed in detail. A model of the deformation-modified grain boundary state is presented.
The ion-plasma deposition was used to produce intermetallic coatings on Al-based substrates. Stru... more The ion-plasma deposition was used to produce intermetallic coatings on Al-based substrates. Structure and properties of these coatings were investigated. It was found that a specific combination of nano-, quasi-, and amorphous intermetallic phases in coatings along with formation of extended transitional sublayer increases mechanical properties of the material. Simultaneously the higher adhesion can be obtained.
Tracer diffusion in ordered intermetallic compounds is reviewed. The main attention is paid to al... more 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 on diffusion in ordered intermetallic compounds are considered. Tracer diffusion in ternary alloys is illustrated for the system Ni–Fe–Al.
Abstract Composition-dependent diffusion coefficients are determined in B2-Ni(CoPt)Al system foll... more Abstract Composition-dependent diffusion coefficients are determined in B2-Ni(CoPt)Al system following the pseudo-binary and pseudo-ternary diffusion couple methods, which would not be possible otherwise in a quaternary inhomogeneous material fulfilling the conditions to solve the equations developed based on the Onsager formalism. The end-member compositions to produce ideal/near-ideal diffusion profiles are chosen based on thermodynamic details. The pseudo-binary interdiffusion coefficients of Ni and Al decrease in the presence of Co but increase in the presence of Pt. The pseudo-ternary interdiffusion coefficients indicate that the main interdiffusion coefficients increase significantly in the presence of Pt. Marginal changes of the cross interdiffusion coefficients substantiate a minor change of the diffusional interactions between the components. The thermodynamic driving forces show opposite trends with respect to composition as compared to the changes of the interdiffusion coefficients advocating a dominating role of the Pt(Co)-induced modifications of point defect concentrations. DFT-based calculations revealed that Pt alloying increases the Ni vacancy concentration and decreases the activation energy for the triple defect diffusion mechanism. These findings explain the increase in the thickness of the interdiffusion zone between the B2-Ni(Pt)Al bond coat and the single crystal superalloy Rene N5 because of Pt addition. Furthermore, the EPMA and TEM analyses reveal the growth of refractory elements-enriched precipitates.
Abstract The recently proposed pair-exchange diffusion model for multicomponent diffusion in a ra... more Abstract 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 pair of elements at the mesoscopic scale. The total fluxes of alloying elements are given as the sum over corresponding pair-contributions, which rely on a set of independent forces and maintain a meaningful symmetric form to satisfy Onsagers reciprocal relations. It is demonstrated that a consistent definition of interdiffusion coefficients requires the fulfillment of the Gibbs-Duhem relation by the applied thermodynamic Gibbs energy description. The expression for the marker velocity for multicomponent random alloy is derived in the pair-wise form as a sum of the differences of chemical potential gradients of two elements with the linear coefficients which are differences between corresponding mobilities. The application of the model to High Entropy Alloys is demonstrated.
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Papers by Sergiy Divinski