Mykola Ivanchenko | VTT Techn. Res. centre of Finland (original) (raw)

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Papers by Mykola Ivanchenko

steel research international, 2010

Hydrogen solubility and diffusion in austenitic stainless steels, namely AISI 310, AISI 301LN and... more Hydrogen solubility and diffusion in austenitic stainless steels, namely AISI 310, AISI 301LN and AISI 201, are studied with thermal desorption spectroscopy (TDS) after electrochemical potentiostatic hydrogen pre-charging. Temperature dependencies of hydrogen desorption for all studied steels manifest a complex main peak caused by hydrogen releasing from the steel lattice by diffusion. Depending on the steel and heating rate the peak is situated from 350 to 500 K and its shape reflects a specific of hydrogen diffusion in stainless steels, which are multicomponent alloys. Analysis of the TDS curves is based on the hydrogen diffusion model taking into account trapping of hydrogen atoms in the energetically deep interstitial positions in the steel crystal lattice. Diffusion coefficient of hydrogen and its total content after the same charging procedure are obtained from the TDS curves and compared for the studied steels.

Journal of Nuclear Materials, 2017

Thermal ageing of nickel-base alloys can lead to the formation of brittle ordered phases, but the... more Thermal ageing of nickel-base alloys can lead to the formation of brittle ordered phases, but the direct study of these phases is challenging. Nanoindentation is used in this study as an alternative technique to determine the extent of short-range ordering (SRO) in thermally aged Alloy 690 TT. Two methods are used for obtaining both qualitative (depth sensitivity) and quantitative (spatial stability) results, which are compared to data from metallography, microhardness and atomic force microscopy in order to discriminate between factors affecting the hardness. When intergranular precipitation and grain size become dominant factors with increasing indentation loads, nanoindentation at low loads enables to distinct within-grain hardness increase related to SRO.

Corrosion Issues in Light Water Reactors, 2007

Intergranular stress corrosion cracking has occurred in BWR environments in non-sensitised, cold-... more Intergranular stress corrosion cracking has occurred in BWR environments in non-sensitised, cold-worked austenitic stainless steel materials. The affecting parameters are so far not fully known, but deformation mechanisms may be decisive. The effect of cold deformation and nitrogen content on the deformation behaviour of austenitic stainless steels was investigated. The materials were austenitic stainless steels of AISI 316L type with different amounts of nitrogen (0.03…0.18%) and they were deformed in tension 0, 5 and 20% before further investigations. The investigations were focused on the dynamic strain ageing (DSA) behaviour as a function of nitrogen level and deformation. A few crack growth rate measurements are performed on nuclear grade AISI 316NG stainless steel with different degrees of deformation (0, 5 and 20%). The effects of DSA on mechanical properties of these materials were evaluated based on peaks in tensile strength and minimum in ductility in the DSA temperature range. Also the strain rate sensitivity in the DSA temperature range was investigated. Internal friction measurements were performed in the temperature range of-100…600 C for determining nitrogen interactions with other alloying elements and dislocations. The results show effects of nitrogen on the stainless steel deformation behaviour, i.e. clear indications of dynamic strain ageing: serrated yielding, negative strain rate sensitivity and changes in the internal friction behaviour as a function of nitrogen content and amount of deformation. The apparent activation energy calculated from the DSA serration occurrence map corresponds to that of nitrogen diffusion. Fully intergranular cracking was obtained in the 20% deformed, nonsensitised AISI 316NG stainless steel in simulated BWRenvironment. The crack growth data and the mechanism are discussed based on the unstable plastic flow of the material.

Materials Science and Engineering: A, 2006

Carbon Snoek-like relaxation peak with a height of about 10 −4 was found in annealed nickel-based... more Carbon Snoek-like relaxation peak with a height of about 10 −4 was found in annealed nickel-based Inconel 600 alloy at 620-670 K while no carbon-induced peaks were observed in Inconel 690 alloy. The activation enthalpy and the pre-exponential factor of the relaxation time are 1.68 ± 0.09 eV and 10 −14.14±0.72 s, respectively. The height of the observed peak increases dramatically, up to about 10 −3 , after tensile deformation of the Inconel 600 alloy at 423 K at the strain rate of 10 −5 s −1 , when dynamic strain aging (DSA) behavior exhibits well developed serrations on the tensile stress-strain curve. Annealing in situ at the carbon peak temperature results in decay of the peak amplitude, which consists of two exponential stages with characteristic times of 1.6 and 21.9 ks, respectively. The first characteristic time is in good agreement with the mean period of DSA serrations. The second characteristic time probably presents the re-growth of carbides partly dissolved during prior deformation in DSA conditions.

Environment-assisted cracking and hot cracking susceptibility of nickel-base alloy weld metals. E... more Environment-assisted cracking and hot cracking susceptibility of nickel-base alloy weld metals. Espoo 2011. VTT Tiedotteita-Research Notes 2582. 152 p.

Journal of Nuclear Materials, 2018

Post-irradiation examination (PIE) in the form of transmission electron microscopy (TEM) was used... more Post-irradiation examination (PIE) in the form of transmission electron microscopy (TEM) was used to characterize the microstructure of several specimens of Zircaloy-2 and Zircaloy-2 plus 1% Nb that had previously underwent in-pile creep testing in the HALDEN reactor. The purpose of the examination was to explore a microstructural basis for an apparent substantially increased rate of hardening over that observed with similar materials in the higher fast-flux environments of the ATR or HFIR, and to investigate the increased creep strength exhibited by the Nb-containing alloy relative to pure Zircaloy-2. The analysis of irradiation-induced defects indicated a higher than expected density, which was consistent with the observed high hardening rate. Modeling based on mean field rate theory suggests the lower neutron flux in the HALDEN reactor results in a higher fraction of irradiation-induced defects being available for sink (loop) nucleation and growth.

Microscopy and Microanalysis, 2015

Dynamic strain aging (DSA) and jerky flow phenomena in the commercial Ni-base alloys Inconel 600 ... more Dynamic strain aging (DSA) and jerky flow phenomena in the commercial Ni-base alloys Inconel 600 and 690 have been investigated. Tensile tests were performed in the strain rate range of 10-3 to 10-6 s-1 at temperatures of 100-600 o C. No remarkable difference in the DSA behaviour of Inconel 600 and 690 alloys was observed. Tensile properties of the studied alloys in the DSA temperature range, and type and characteristics of jerky flow were obtained and analysed. The map for occurrence of serrated flow as a function of strain rate and temperature was built for Inconel 600 and 690 alloys and the activation enthalpies of dynamic strain aging appearance were found to be 1.6 eV for both materials. The obtained enthalpy of DSA appearance corresponds well to the enthalpy of carbon diffusion (1.76 eV), which was estimated by means of internal friction for the studied Inconel 600 alloy. The mechanisms of DSA based on interstitial atom interactions with dislocations in the studied alloys are discussed and the results are analysed based on the susceptibility of these alloys to environmentally assisted cracking (EAC).

International Conference on Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment, 2016

Bulletin of Kharkov National Automobile and Highway University, 2021

A significant number of heat and power equipment, including welded connections of steam pipelines... more A significant number of heat and power equipment, including welded connections of steam pipelines made of 15x1m1f and 12x1mf Steels, have now reached the design service life. Their practical experience is about 200,000 hours at an estimated temperature of 545°C, and the park resource according to regulatory documentation is 250,000 hours. Note that aging welded joints are operated in conditions of start-ups and stops, which have become more frequent, which contributes to an increase in the intensity of their damage. In this connection, the question arose about the possibility of their operation longer than the estimated period in the new conditions. Goal. The goal is study of the features of damage to welded elements of steam pipelines operating in conditions of creep and low cycle fatigue. Methodology. The study of samples from existing damaged steam pipelines was carried out by the method of structural analysis, based on the consideration of the processes of structural and phase c...

steel research international, 2010

Hydrogen solubility and diffusion in austenitic stainless steels, namely AISI 310, AISI 301LN and... more Hydrogen solubility and diffusion in austenitic stainless steels, namely AISI 310, AISI 301LN and AISI 201, are studied with thermal desorption spectroscopy (TDS) after electrochemical potentiostatic hydrogen pre-charging. Temperature dependencies of hydrogen desorption for all studied steels manifest a complex main peak caused by hydrogen releasing from the steel lattice by diffusion. Depending on the steel and heating rate the peak is situated from 350 to 500 K and its shape reflects a specific of hydrogen diffusion in stainless steels, which are multicomponent alloys. Analysis of the TDS curves is based on the hydrogen diffusion model taking into account trapping of hydrogen atoms in the energetically deep interstitial positions in the steel crystal lattice. Diffusion coefficient of hydrogen and its total content after the same charging procedure are obtained from the TDS curves and compared for the studied steels.

Journal of Nuclear Materials, 2017

Thermal ageing of nickel-base alloys can lead to the formation of brittle ordered phases, but the... more Thermal ageing of nickel-base alloys can lead to the formation of brittle ordered phases, but the direct study of these phases is challenging. Nanoindentation is used in this study as an alternative technique to determine the extent of short-range ordering (SRO) in thermally aged Alloy 690 TT. Two methods are used for obtaining both qualitative (depth sensitivity) and quantitative (spatial stability) results, which are compared to data from metallography, microhardness and atomic force microscopy in order to discriminate between factors affecting the hardness. When intergranular precipitation and grain size become dominant factors with increasing indentation loads, nanoindentation at low loads enables to distinct within-grain hardness increase related to SRO.

Corrosion Issues in Light Water Reactors, 2007

Intergranular stress corrosion cracking has occurred in BWR environments in non-sensitised, cold-... more Intergranular stress corrosion cracking has occurred in BWR environments in non-sensitised, cold-worked austenitic stainless steel materials. The affecting parameters are so far not fully known, but deformation mechanisms may be decisive. The effect of cold deformation and nitrogen content on the deformation behaviour of austenitic stainless steels was investigated. The materials were austenitic stainless steels of AISI 316L type with different amounts of nitrogen (0.03…0.18%) and they were deformed in tension 0, 5 and 20% before further investigations. The investigations were focused on the dynamic strain ageing (DSA) behaviour as a function of nitrogen level and deformation. A few crack growth rate measurements are performed on nuclear grade AISI 316NG stainless steel with different degrees of deformation (0, 5 and 20%). The effects of DSA on mechanical properties of these materials were evaluated based on peaks in tensile strength and minimum in ductility in the DSA temperature range. Also the strain rate sensitivity in the DSA temperature range was investigated. Internal friction measurements were performed in the temperature range of-100…600 C for determining nitrogen interactions with other alloying elements and dislocations. The results show effects of nitrogen on the stainless steel deformation behaviour, i.e. clear indications of dynamic strain ageing: serrated yielding, negative strain rate sensitivity and changes in the internal friction behaviour as a function of nitrogen content and amount of deformation. The apparent activation energy calculated from the DSA serration occurrence map corresponds to that of nitrogen diffusion. Fully intergranular cracking was obtained in the 20% deformed, nonsensitised AISI 316NG stainless steel in simulated BWRenvironment. The crack growth data and the mechanism are discussed based on the unstable plastic flow of the material.

Materials Science and Engineering: A, 2006

Carbon Snoek-like relaxation peak with a height of about 10 −4 was found in annealed nickel-based... more Carbon Snoek-like relaxation peak with a height of about 10 −4 was found in annealed nickel-based Inconel 600 alloy at 620-670 K while no carbon-induced peaks were observed in Inconel 690 alloy. The activation enthalpy and the pre-exponential factor of the relaxation time are 1.68 ± 0.09 eV and 10 −14.14±0.72 s, respectively. The height of the observed peak increases dramatically, up to about 10 −3 , after tensile deformation of the Inconel 600 alloy at 423 K at the strain rate of 10 −5 s −1 , when dynamic strain aging (DSA) behavior exhibits well developed serrations on the tensile stress-strain curve. Annealing in situ at the carbon peak temperature results in decay of the peak amplitude, which consists of two exponential stages with characteristic times of 1.6 and 21.9 ks, respectively. The first characteristic time is in good agreement with the mean period of DSA serrations. The second characteristic time probably presents the re-growth of carbides partly dissolved during prior deformation in DSA conditions.

Environment-assisted cracking and hot cracking susceptibility of nickel-base alloy weld metals. E... more Environment-assisted cracking and hot cracking susceptibility of nickel-base alloy weld metals. Espoo 2011. VTT Tiedotteita-Research Notes 2582. 152 p.

Journal of Nuclear Materials, 2018

Post-irradiation examination (PIE) in the form of transmission electron microscopy (TEM) was used... more Post-irradiation examination (PIE) in the form of transmission electron microscopy (TEM) was used to characterize the microstructure of several specimens of Zircaloy-2 and Zircaloy-2 plus 1% Nb that had previously underwent in-pile creep testing in the HALDEN reactor. The purpose of the examination was to explore a microstructural basis for an apparent substantially increased rate of hardening over that observed with similar materials in the higher fast-flux environments of the ATR or HFIR, and to investigate the increased creep strength exhibited by the Nb-containing alloy relative to pure Zircaloy-2. The analysis of irradiation-induced defects indicated a higher than expected density, which was consistent with the observed high hardening rate. Modeling based on mean field rate theory suggests the lower neutron flux in the HALDEN reactor results in a higher fraction of irradiation-induced defects being available for sink (loop) nucleation and growth.

Microscopy and Microanalysis, 2015

Dynamic strain aging (DSA) and jerky flow phenomena in the commercial Ni-base alloys Inconel 600 ... more Dynamic strain aging (DSA) and jerky flow phenomena in the commercial Ni-base alloys Inconel 600 and 690 have been investigated. Tensile tests were performed in the strain rate range of 10-3 to 10-6 s-1 at temperatures of 100-600 o C. No remarkable difference in the DSA behaviour of Inconel 600 and 690 alloys was observed. Tensile properties of the studied alloys in the DSA temperature range, and type and characteristics of jerky flow were obtained and analysed. The map for occurrence of serrated flow as a function of strain rate and temperature was built for Inconel 600 and 690 alloys and the activation enthalpies of dynamic strain aging appearance were found to be 1.6 eV for both materials. The obtained enthalpy of DSA appearance corresponds well to the enthalpy of carbon diffusion (1.76 eV), which was estimated by means of internal friction for the studied Inconel 600 alloy. The mechanisms of DSA based on interstitial atom interactions with dislocations in the studied alloys are discussed and the results are analysed based on the susceptibility of these alloys to environmentally assisted cracking (EAC).

International Conference on Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment, 2016

Bulletin of Kharkov National Automobile and Highway University, 2021

A significant number of heat and power equipment, including welded connections of steam pipelines... more A significant number of heat and power equipment, including welded connections of steam pipelines made of 15x1m1f and 12x1mf Steels, have now reached the design service life. Their practical experience is about 200,000 hours at an estimated temperature of 545°C, and the park resource according to regulatory documentation is 250,000 hours. Note that aging welded joints are operated in conditions of start-ups and stops, which have become more frequent, which contributes to an increase in the intensity of their damage. In this connection, the question arose about the possibility of their operation longer than the estimated period in the new conditions. Goal. The goal is study of the features of damage to welded elements of steam pipelines operating in conditions of creep and low cycle fatigue. Methodology. The study of samples from existing damaged steam pipelines was carried out by the method of structural analysis, based on the consideration of the processes of structural and phase c...