Browsing by Author "Yagodzinskyy, Yuriy"
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- Determination of critical hydrogen concentration and its effect on mechanical performance of 2200 mpa and 600 hbw martensitic ultra‐high‐strength steel
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-06-20) Fangnon, Eric; Yagodzinskyy, Yuriy; Malictki, Evgenii; Mehtonen, Saara; Virolainen, Esa; Vilaça, PedroThe influence of hydrogen on the mechanical performance of a hot‐rolled martensitic steel was studied by means of constant extension rate test (CERT) and constant load test (CLT) followed with thermal desorption spectroscopy measurements. The steel shows a reduction in tensile strength up to 25% of ultimate tensile strength (UTS) at critical hydrogen concentrations determined to be about 1.1 wt.ppm and 50% of UTS at hydrogen concentrations of 2 wt.ppm. No further strength degradation was observed up to hydrogen concentrations of 4.8 wt.ppm. It was observed that the interplay between local hydrogen concentrations and local stress states, accompanied with the presence of total average hydrogen reducing the general plasticity of the specimen are responsible for the observed strength degradation of the steel at the critical concentrations of hydrogen. Under CLT, the steel does not show sensitivity to hydrogen at applied loads below 50% of UTS under contin-uous electrochemical hydrogen charging up to 85 h. Hydrogen enhanced creep rates during constant load increased linearly with increasing hydrogen concentration in the steel. - Effect of prior austenite grain morphology on hydrogen embrittlement behaviour under plastic straining in as-quenched 500 HBW steels
A4 Artikkeli konferenssijulkaisussa(2022) Latypova, Renata; Nyo, Tun Tun; Seppälä, Oskari; Fangnon, Eric; Yagodzinskyy, Yuriy; Mehtonen, Saara; Hänninen, Hannu; Kömi, Jukka; Pallaspuro, SakariPrior austenite grain (PAG) structure is an important factor influencing hydrogen embrittlement (HE) susceptibility of ultrahigh-strength steels. In this study, the effect of PAG shape and size on HE behaviour is investigated using a novel tuning-fork testing method and hydrogen thermal desorption spectroscopy (TDS). Different PAG structures were acquired via re-austenitization (860 °C = A860, 960 °C = A960) and rapid quenching of an as-received 500 HBW direct-quenched (DQ) steel, which has an auto-tempered lath-martensitic microstructure and elongated PAG morphology. Fractography reveals different crack propagation mechanisms depending on the PAG shape. With the elongated PAG structure, hydrogen-induced crack propagation transverse to elongated PAGs was transgranular quasi-cleavage. Propagation was partially intergranular with the equiaxed PAG structures, regardless of the PAG size, leading to equally faster fracture. The TDS results show that there are no significant differences between the total hydrogen contents, but re-austenitized A860 and A960 steels contain a higher fraction of weakly trapped hydrogen. This indicates that the PAG boundaries are not the dominant hydrogen traps, and the different crack propagation mechanisms are rather linked to the geometrical shape of the grain structure. - Gamma radiation induces hydrogen absorption by copper in water
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016-04-18) Lousada, Cláudio M.; Soroka, Inna L.; Yagodzinskyy, Yuriy; Tarakina, Nadezda V.; Todoshchenko, Olga; Hänninen, Hannu; Korzhavyi, Pavel A.; Jonsson, MatsOne of the most intricate issues of nuclear power is the long-term safety of repositories for radioactive waste. These repositories can have an impact on future generations for a period of time orders of magnitude longer than any known civilization. Several countries have considered copper as an outer corrosion barrier for canisters containing spent nuclear fuel. Among the many processes that must be considered in the safety assessments, radiation induced processes constitute a key-component. Here we show that copper metal immersed in water uptakes considerable amounts of hydrogen when exposed to γ-radiation. Additionally we show that the amount of hydrogen absorbed by copper depends on the total dose of radiation. At a dose of 69 kGy the uptake of hydrogen by metallic copper is 7 orders of magnitude higher than when the absorption is driven by H2(g) at a pressure of 1 atm in a non-irradiated dry system. Moreover, irradiation of copper in water causes corrosion of the metal and the formation of a variety of surface cavities, nanoparticle deposits, and islands of needle-shaped crystals. Hence, radiation enhanced uptake of hydrogen by spent nuclear fuel encapsulating materials should be taken into account in the safety assessments of nuclear waste repositories. - Hydrogen Degradation of Ferrous Alloys
Insinööritieteiden ja arkkitehtuurin tiedekunta | Bachelor's thesis(2010) Julin, Mika - Hydrogen effects in equiatomic CrFeNiMn alloy fabricated by laser powder bed fusion
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-06) Yang, Xuan; Yagodzinskyy, Yuriy; Ge, Yanling; Lu, Eryang; Lehtonen, Joonas; Kollo, Lauri; Hannula, Simo-PekkaThis study investigates the effects of laser powder bed fusion (LPBF) on the hydrogen uptake of the face-centered cubic (FCC) equiatomic CrFeNiMn multicomponent alloy after cathodic hydrogen charging (HC). Hydrogen desorption was evaluated using thermal desorption spectroscopy (TDS), and microstructural changes after the TDS test were examined. Results reveal that the amount of hydrogen absorbed by LPBF CrFeNiMn alloy was significantly higher than that in pulsed electric current sintered (PECS) CrFeNiMn alloy or in conventional 316L austenitic stainless steel. The observations are ascribed to the differences in the amount of hydrogen absorbed by the multicomponent lattice, dislocation densities, width of segregation range at cell walls created by the rapid cooling in LBPF, and vacancies remaining after cooling to room temperature. A hydrogen-charged LBPF transmission electron microscope (TEM) specimen was also characterized. Stacking faults and cracks along the (111)-planes of austenite were observed. Scanning electron microscopy (SEM) of the surface of the TDS-tested samples also indicated hydrogen-induced cracks and hydrogen-induced submicron pits at the grain boundary inclusions. - Hydrogen Effects on Austenitic Stainless Steels and High-Strength Carbon Steels
School of Engineering | Doctoral dissertation (article-based)(2015) Todoshchenko, OlgaThe resistance to hydrogen embrittlement is an important factor in the development of new steel grades for a variety of applications. The thesis describes investigations on hydrogen effects on two classes of steels - austenitic stainless steels and advanced high-strength carbon steels. Hydrogen solubility and diffusion in metastable austenitic stainless steels are studied with thermal desorption spectroscopy (TDS). This method, together with the mathematical modeling of the processes of hydrogen uptake and desorption, allows to analyse hydrogen diffusion and trapping in a metal. Temperature dependencies of hydrogen desorption for the studied steels manifest a complex peak. Specific features of hydrogen uptake and desorption for a multi-component alloy in comparison with that for pure metals are analysed by the proposed model. It was found that plastic strain affects the shape of the TDS peak for all the studied materials. In metastable austenitic stainless steels the parameters of hydrogen diffusion and trapping in martensite phase, which is forming under pre-straining, were estimated by the proposed model. High-strength carbon steels of the strength level from 1000 to 1400 MPa with different contents of Ti were studied. It was found that there is an optimal content and size distribution of Ti-based non-metallic inclusions (NMI) when the steel is most resistant to hydrogen embrittlement. Fractography of the studied steels shows that the fracture mechanism depends on the chemical composition of the studied steels and hydrogen-induced cracking exhibits intergranular or transgranular character occurring often in the form of hydrogen flakes. It was found that hydrogen-induced cracks of the hydrogen flakes initiate at Ti-based NMIs. TDS analysis evidences that the main trapping sites for hydrogen in the high-strength carbon steels are NMI interfaces. The mechanisms of hydrogen interaction with NMIs are discussed. All the studied high-strength carbon steels are sensitive to hydrogen under slow strain rate tensile tests. Constant load tests show that different processes influence on hydrogen-induced fracture at low and high applied stresses for the high-strength carbon steels with high Ti-alloying. Tempered high-strength carbon steels are less sensitive to hydrogen embrittlement than their non-tempered counterparts. - Hydrogen effects on mechanical performance of nodular cast iron
Insinööritieteiden korkeakoulu | Master's thesis(2020-05-18) Sahiluoma, PatrikThe ferritic nodular cast iron EN 1563 grade EN-GJS-400-15U, intended for use as the material for the load-bearing inserts of canisters for long-term geological disposal of spent nuclear fuel, was studied in order to evaluate its sensitivity to hydrogen-induced effects on mechanical performance. In the KBS-3 method, the internal structural nodular cast iron insert provides the mechanical strength against external loads, whereas the copper shell (50 mm thick) provides a barrier against corrosion. Hydrogen was charged electrochemically in the nodular cast iron from 0.1N H2SO4 solution both in free corrosion and under controlled cathodic potential. Hydrogen uptake and trapping were measured using thermal desorption spectroscopy. It was found that the hydrogen desorption rate after hydrogen charging manifests two distinct peaks located around 400 K and 500 K when using heating rate of 10 K/min. It was also observed that plastic deformation of the specimens during continuous hydrogen charging results in a remarkable increase of hydrogen uptake. Especially the role of the graphite nodules in hydrogen uptake was examined. Slow strain rate tests (SSRT) and constant load tests (CLT) performed under continuous electrochemical hydrogen charging show that hydrogen reduces the elongation to fracture in SSRT and time to fracture in CLT. It was also observed that hydrogen dramatically increases the strain rate of the ductile cast iron in CLT at applied load of about 0.5 tensile strength. The hydrogen-induced cracking appearance in the tensile specimens was characterized with fractography after tensile testing. In the ferrite phase, the fracture mode was cleavage fracture initiating from the interphases of the graphite nodules. The obtained results are discussed in terms of the role of hydrogen and the graphite nodules in mechanical performance of ductile cast iron. - Hydrogen embrittlement of nodular cast iron
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-01) Sahiluoma, Patrik; Yagodzinskyy, Yuriy; Forsström, Antti; Hänninen, Hannu; Bossuyt, SvenFerritic nodular cast iron, intended for use as the material for inserts of canisters for long-term geological disposal of spent nuclear fuel, was studied for hydrogen sensitivity. In the canisters, the insert provides the mechanical strength against external loads. Hydrogen was charged from 0.1 N H(2)SO(4)solution in free-corrosion tests and under controlled cathodic potential. Hydrogen uptake and trapping were then measured using thermal desorption spectroscopy. The hydrogen desorption rate after hydrogen charging manifests two distinct peaks. Plastic deformation during hydrogen charging increases the hydrogen uptake considerably. Hydrogen reduces the elongation to fracture and time to fracture in slow strain rate testing and constant load testing (CLT), respectively. Especially, the strain rate in CLT is dramatically increased. The appearance of hydrogen-induced cracking in the ferrite phase changes from ductile dimple fracture to brittle cleavage fracture due to hydrogen charging, which initiates from the interphases of the graphite nodules. The results are discussed in terms of the role of hydrogen and the graphite nodules in hydrogen embrittlement of ductile cast iron. - Hydrogen uptake and its effect on mechanical properties of 18% Cr ferritic stainless steel
A4 Artikkeli konferenssijulkaisussa(2017) Malitckii, Evgenii; Yagodzinskyy, Yuriy; Lehto, Pauli; Remes, Heikki; Hänninen, Hannu - Hydrogen-induced micro-void formation in copper used for spent nuclear fuel disposal canisters
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023-02) Sahiluoma, Patrik; Yagodzinskyy, Yuriy; Bossyut, Sven; Hänninen, HannuSpent nuclear fuel is planned to be deposited in the 50 mm thick copper canisters at about 500 m depth in the bedrock. Hydrogen uptake may occur in the disposal conditions in copper due to corrosion reactions and effects of irradiation. Therefore, it is important to know in which conditions the hydrogen uptake results in the formation of pressurized hydrogen bubbles near the copper surface. During the thermal desorption spectroscopy (TDS) measurements the existing hydrogen bubbles grow due to accumulation of dissolved hydrogen and build-up of hydrogen gas pressure inside the voids. The further growth of the voids occurs by plastic deformation and results opening of the voids near the copper surface due to increasing temperature. The friction-stir weld metal samples of phosphorous-doped oxygen-free copper were cathodically charged with hydrogen in a 1.0 N H2SO4 solution with added 10 mg/L thiourea at various electrochemical potentials, -0.95…-1.3 VSCE. A threshold potential of -1.10 VSCE was found for the marked increase of hydrogen uptake and hydrogen-induced void formation near the copper surface. - Improved accuracy of thermal desorption spectroscopy by specimen cooling during measurement of hydrogen concentration in a high-strength steel
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-03-10) Fangnon, Eric; Malitckii, Evgenii; Yagodzinskyy, Yuriy; Vilaça, PedroThermal desorption spectroscopy (TDS) is a powerful method for the measurement of hydrogen concentration in metallic materials. However, hydrogen loss from metallic samples during the preparation of the measurement poses a challenge to the accuracy of the results, especially in materials with high diffusivity of hydrogen, like ferritic and ferritic-martensitic steels. In the present paper, the effect of specimen cooling during the experimental procedure, as a tentative to reduce the loss of hydrogen during air-lock vacuum pumping for one high-strength steel of 1400 MPa, is evaluated. The results show, at room temperature, the presence of a continuous outward hydrogen flux accompanied with the redistribution of hydrogen within the measured steel during its exposure to the air-lock vacuum chamber under continuous pumping. Cooling of the steel samples to 213 K during pumping in the air-lock vacuum chamber before TDS measurement results in an increase in the measured total hydrogen concentration at about 14%. A significant reduction in hydrogen loss and redistribution within the steel sample improves the accuracy of hydrogen concentration measurement and trapping analysis in ferritic and martensitic steels. - Role of retained austenite in hydrogen trapping and hydrogen-assisted fatigue fracture of high-strength steels
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-07-08) Malitckii, Evgenii; Yagodzinskyy, Yuriy; Vilaҫa, PedroThe Interaction of hydrogen with retained austenite under fatigue loading of dual-phase and complex-phase high-strength steels with strength of about 1200 MPa was studied. A load-controlled fatigue test was performed in the air with the maximum applied tensile strength of 900 MPa, which is just below the offset yield point of the studied steels. The trapping of hydrogen accumulated into the studied steels under the fatigue loading was studied by thermal desorption spectroscopy. Measurements of hydrogen trapping evolution and microstructure changes during fatigue testing reveal a complicated hydrogen trapping behavior driven by hydrogen interaction with deformation defects and retained austenite. Hydrogen concentration increases in the studied steels during the fatigue testing in the air without preceding hydrogen charging. The fracture surfaces were studied by scanning electron microscopy evidencing the relationship between the hydrogen concentration increase related to retained austenite and initiation of the intergranular fatigue fracture. The role of retained austenite in hydrogen-assisted fatigue cracking is discussed and a possible mechanism of the hydrogen-assisted fatigue crack initiation in the high-strength steels is proposed. - Selective laser melting of duplex stainless Steel 2205 : Effect of post-processing heat treatment on microstructure, mechanical properties, and corrosion resistance
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-08-01) Papula, Suvi; Song, Mingshi; Pateras, Aaron; Chen, Xiao Bo; Brandt, Milan; Easton, Mark; Yagodzinskyy, Yuriy; Virkkunen, Iikka; Hänninen, HannuAdditive manufacturing (AM) is a rapidly growing field of technology. In order to increase the variety of metal alloys applicable for AM, selective laser melting (SLM) of duplex stainless steel 2205 powder and the resulting microstructure, density, mechanical properties, and corrosion resistance were investigated. An optimal set of processing parameters for producing high density (> 99.9%) material was established. Various post-processing heat treatments were applied on the as-built predominantly ferritic material to achieve the desired dual-phase microstructure. Effects of annealing at temperatures of 950 °C, 1000 °C, 1050 °C, and 1100 °C on microstructure, crystallographic texture, and phase balance were examined. As a result of annealing, 40-46 vol.% of austenite phase was formed. Annealing decreased the high yield and tensile strength values of the as-built material, but significantly increased the ductility. Annealing also decreased the residual stresses in the material. Mechanical properties of the SLM-processed and heat-treated materials outperformed those of conventionally produced alloy counterparts. Using a scanning strategy with 66° rotation between layers decreased the strength of the crystallographic texture. Electrochemical cyclic potentiodynamic polarization testing in 0.6 M NaCl solution at room temperature showed that the heat treatment improved the pitting corrosion resistance of the as-built SLM-processed material. - Sulphide-induced stress corrosion cracking and hydrogen absorption of copper in deoxygenated water at 90°C
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-01) Forsström, Antti; Becker, Richard; Hänninen, Hannu; Yagodzinskyy, Yuriy; Heikkilä, MikkoStress corrosion cracking (SCC) of oxygen-free phosphorous-alloyed copper was investigated in sulphide- and chloride-containing deoxygenated water at 90°C with sulphide concentrations of 0.001 and 0.00001 M. Several intergranular defects were found in the specimen exposed to the high sulphide environment. Similar defects were not found in the low sulphide environment, where only slight corrosion on grain boundaries and slip lines occurred. Hydrogen content measurements show an increase in hydrogen uptake of the plastically deformed specimens, which is dependent on the sulphide concentration and on plastic deformation of copper. However, the highest hydrogen content was measured in friction stir welds, welded in air without shielding gas, and tested in the high sulphide environment. The embedded oxide particles in the weld metal act as local hydrogen trapping sites and selectively react with the sulphide solution. A relatively thick air-formed oxide film covers the copper canisters when deposited, which transforms into a sulphide film in the repository conditions. Thus, some of the coupon specimens were pre-oxidised. The conversion of the pre-existing Cu2O film into Cu2S film occurs quickly and the transformation is almost 100% efficient. The structure and properties of the Cu2S films, susceptibility of copper to sulphide-induced SCC and hydrogen uptake of copper in reducing, anoxic repository conditions are discussed.