Aaltodoc Repository :: Browsing by Author "Malitckii, Evgenii"

Browsing by Author "Malitckii, Evgenii"

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Evaluation of steels susceptibility to hydrogen embrittlement: A thermal desorption spectroscopy-based approach coupled with artificial neural network
(MDPI AG, 2020-12-02) Malitckii, Evgenii; Fangnon, Eric; Vilaça, Pedro; Department of Mechanical Engineering; Advanced Manufacturing and Materials
A novel approach has been developed for quantitative evaluation of the susceptibility of steels and alloys to hydrogen embrittlement. The approach uses a combination of hydrogen thermal desorption spectroscopy (TDS) analysis with recent advances in machine learning technology to develop a regression artificial neural network (ANN) model predicting hydrogen-induced degradation of mechanical properties of steels. We describe the thermal desorption data processing, artificial neural network architecture development, and the learning process beneficial for the accuracy of the developed artificial neural network model. A data augmentation procedure was proposed to increase the diversity of the input data and improve the generalization of the model. The study of the relationship between thermal desorption spectroscopy data and the mechanical properties of steel evidences a strong correlation of their corresponding parameters. A prototype software application based on the developed model is introduced and is openly available. The developed prototype based on TDS analysis coupled with ANN is shown to be a valuable engineering tool for steel characterization and quantitative prediction of the degradation of steel properties caused by hydrogen.
Full-field Strain Measurements for Microstructurally Small Fatigue Crack Propagation Using Digital Image Correlation Method
(JOURNAL OF VISUALIZED EXPERIMENTS, 2019-01-16) Malitckii, Evgenii; Remes, Heikki; Lehto, Pauli; Bossuyt, Sven; Advanced Manufacturing and Materials; Marine Technology; Department of Mechanical Engineering
A novel measurement approach is used to reveal the cumulative deformation field at a sub-grain level and to study the influence of microstructure on the growth of microstructurally small fatigue cracks. The proposed strain field analysis methodology is based on the use of a unique pattering technique with a characteristic speckle size of approximately 10 µm. The developed methodology is applied to study the small fatigue crack behavior in body centered cubic (bcc) Fe-Cr ferritic stainless steel with a relatively large grain size allowing a high spatial measurement accuracy at the sub-grain level. This methodology allows the measurement of small fatigue crack growth retardation events and associated intermittent shear strain localization zones ahead of the crack tip. In addition, this can be correlated with the grain orientation and size. Thus, the developed methodology can provide a deeper fundamental understanding of the small fatigue crack growth behavior, required for the development of robust theoretical models for the small fatigue crack propagation in polycrystalline materials.
Hydrogen and helium effects on reduced activation Fe-Cr ferrite-martensite and ODS steels
(Aalto University, 2015) Malitckii, Evgenii; Yagodzinskyy, Yuriy, Dr.; Koneenrakennustekniikan laitos; Department of Engineering Design and Production; Engineering Materials; Insinööritieteiden korkeakoulu; School of Engineering; Hänninen, Hannu, Prof., Aalto University, Department of Engineering Design and Production, Finland
Significant amounts of hydrogen and helium are generated in the structural materials of the nuclear reactor systems by the interaction of the alloying elements with both fast and thermal neutrons. Hydrogen can also be effectively absorbed by other environmental processes. Helium and hydrogen stabilize the small vacancy clusters and facilitate the further formation of the voids that causes the swelling of the structural steels. At the same time, hydrogen plays an important role in degradation of the mechanical properties of the structural steels due to the hydrogen embrittlement (HE). In the thesis, the deleterious effects of hydrogen and helium are studied on the reduced activation ferrite-martensite (RAFM) and oxide dispersion strengthened (ODS) RAFM steels, which are promising materials for Gen IV nuclear reactor systems. Hydrogen and helium uptake in RAFM and ODS-RAFM steels are studied by thermal desorption spectroscopy (TDS) evidencing the higher hydrogen and helium concentration in ODS-RAFM steel after hydrogen charging and helium irradiation, respectively, than that observed in the base RAFM steel. Activation analyses for the hydrogen and helium desorption are performed using the obtained TDS curves. Possible role of the dispersoid phase of yttrium oxide nanoparticles in hydrogen and helium trapping is discussed. Mechanical properties of the RAFM and ODS-RAFM steels are studied in terms of their sensitivity to hydrogen embrittlement after electrochemical hydrogen charging at room temperature (RT). The obtained results evidence that there is a critical hydrogen concentration above which the ODS steel suffers from hydrogen embrittlement in form of intergranular fracture. The instrument for hydrogen charging from glow discharge plasma is developed and the suitable conditions of hydrogen charging were obtained experimentally. The mechanical properties of RAFM and ODS-RAFM steels are studied during continuous hydrogen charging using the developed hydrogen charging process instrument at room and elevated temperatures. Sensitivity to HE of the ODS steel is found to be less pronounced at elevated temperatures compared with that at RT, while the susceptibility to hydrogen of the matrix material remains approximately the same at all the testing temperatures. Hydrogen-induced cracking in the studied steels initiates preferably from non-metallic inclusions (NMI) such as chromium and tungsten carbide particles. Possible mechanism of hydrogen interaction with NMIs is discussed.
Hydrogen uptake and its effect on mechanical properties of 18% Cr ferritic stainless steel
(2017) Malitckii, Evgenii; Yagodzinskyy, Yuriy; Lehto, Pauli; Remes, Heikki; Hänninen, Hannu; Department of Mechanical Engineering; Somerday, B.P.; Sofronis, P.
Improved accuracy of thermal desorption spectroscopy by specimen cooling during measurement of hydrogen concentration in a high-strength steel
(MDPI AG, 2020-03-10) Fangnon, Eric; Malitckii, Evgenii; Yagodzinskyy, Yuriy; Vilaça, Pedro; Department of Mechanical Engineering; Advanced Manufacturing and Materials
Thermal 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.
Influence of microstructural deformation mechanisms and shear strain localisations on small fatigue crack growth in ferritic stainless steel
(ELSEVIER SCI LTD, 2022-10) Gallo, Pasquale; Lehto, Pauli; Malitckii, Evgenii; Remes, Heikki; Department of Mechanical Engineering; Marine Technology; Solid Mechanics; Advanced Manufacturing and Materials
Microstructurally small fatigue crack growth (FCG) rate in body-centred cubic (BCC) ferritic stainless steel is investigated by using a novel domain misorientation approach for EBSD microstructural deformation analyses, in conjunction with in situ digital imaging correlation (DIC). The DIC analyses revealed that shear strain local- isations occur ahead of the crack tip during propagation and correlate well with the FCG rate retardations. Grain boundaries can be found at both peaks and valleys of the FCG rate curve and alter the interaction between crack growth and shear strain localisations. At the microstructural level, the deformation is associated with the dislocation-mediated plastic deformation process, showing increased formation of grain sub-structures in the regions of the strain localisation. Consequently, material experiences local hardening causing the FCG retarda- tion events. If the crack avoids the hardened material region through a macroscopic cross-slip mechanism, retardation is minor. On the contrary, if the crack penetrates the hardened region, retardation is significant.
Influence of sample extraction location on thermal desorption spectroscopy from a heat-resistant 13CrMo4-5 steel plate and correlation with microstructure features
(Elsevier, 2024-08) Silva, Maria I.; Malitckii, Evgenii; Lehto, Pauli; Vilaça, Pedro; Department of Mechanical Engineering; Materials to Products; Advanced Manufacturing and Materials; Marine and Arctic Technology
Thermal desorption spectroscopy (TDS) is a highly sensitive and widely used method to directly measure the total hydrogen concentration and indirectly assess the hydrogen trapping sites and mechanisms from the spectra features in steels. Thus, there is a need to investigate the influence of sample location from a 5 mm plate of hot-rolled heat-resistant structural steel on TDS spectra. Via a new highly sensitive and specific correlation coefficient (microToH), the TDS results are correlated with low-angle grain boundaries volume fraction, grain size with different misorientation thresholds, microhardness, and geometrically necessary dislocations at different densities. The results indicate that sample location influences 133 % and 62 % in the hydrogen desorption of peak 1 (at 515 K), and total hydrogen concentration via the influence of peak 2 (at 634 K), respectively. Thus, sample location needs to be considered as one relevant aspect in a research plan based on TDS analysis. The influence on peak 3 (at 762 K) was found to be negligible as it is related to the first exothermic peak of the heating cycle, associated with carbide precipitation phenomena. The individual grain analysis performed with high-resolution adaptive DMM and GND maps emphasises the accumulation of the deformation in the ferritic domain at the vicinity of the pearlite structures.
Measurement of microstructurally small fatigue crack using digital image correlation
(2021-06-14) Tillikainen, Ilari; Malitckii, Evgenii; Lehto, Pauli; Insinööritieteiden korkeakoulu; Remes, Heikki
Modern manufacturing methods enable the production of components, where microstructurally small cracks determine a substantial amount of their fatigue life. The current fatigue assessment approaches focus mainly on long cracks, which are insufficient to characterise the microstructurally small cracks’ behaviour. More experimental research throughout the fatigue life is needed to deepen our understanding of the behaviour of microstructurally small crack. This thesis focused on the experimental characterisation of microstructurally small fatigue crack’s behaviour. The research objective was to develop a holistic measurement procedure for small fatigue cracks. The methodology was based on digital image correlation (DIC) and subsequent crack growth analyses within individual grains. A synchronized dual-camera setup was developed to measure in-situ crack length and full-field displacements during the crack growth. The microstructure was studied using EBSD, and the obtained grain boundary map was compared to the shear strain localisation data acquired using DIC. The developed experimental procedure was applied for a Fe 18%Cr stainless steel specimen with a volume-weighted average grain size of 192 µm. The specimen was subjected to cyclic loading at a load ratio of 0.1 and load frequency of 10 Hz. The developed experimental procedures and statistical analysis was used to successfully measure the crack length, crack growth rate (CGR) and crack-tip opening displacement range (ΔCTOD). Both CGR and ΔCTOD were highly affected by microstructural features, i.e. grain boundaries or shear strain localisations. On smaller crack lengths, the shear strain localisations develop along the crack path well before the crack tip reached the localisation. The grain boundaries restricted the crack-tip plasticity on longer crack lengths, which formed large shear strain localisations. Shear strain localisation’s vicinity at the crack tip led to significant variation in CGR and ΔCTOD throughout the crack propagation. The observations obtained by the developed experimental procedures help to explain the fundamental mechanisms behind the distinct behaviour of small fatigue cracks.
Method of hydrogen loss reduction for TDS apparatus
(2018-10-29) Fangnon, Agbemon; Malitckii, Evgenii; Insinööritieteiden korkeakoulu; Vilaça, Pedro
Hydrogen embrittlement is a major concern for many engineering applications, especially the steel industry. Steels during production and in service are susceptible to cracks and fissure as a result of the effect of hydrogen diffusion and trapping in them. The use of high strength steels by the automobile industry, the search for suitable materials for nuclear applications and the selection of materials for hydrogen storage tanks form strong basis for research on the effect of hydrogen on metallic materials. There are many technics for the investigation of hydrogen concentration, trapping behavior and embrittlement mechanisms. Thermal desorption spectroscopy (TDS) is a technique reliably used to investigate hydrogen interaction with metallic materials. With this technique the samples are measured in an ultra-high vacuum chamber (UVH). The specimen are first loaded in an air-lock, pumped to an intermediate vacuum pressure, to prevent the contamination of the UHV chamber. Hydrogen escape from specimens during air-lock dwelling time in the interim of the TDS procedure was investigated. The hydrogen loss during TDS procedure for Ferritic steel ASTM UNS S43940, as-supplied ferritic- martensitic steel, H-charged ferritic-Martensitic steel and AISI 304 austenitic steel was measured. The specimens of each material were measured consequently with an air-lock dwelling time of 10, 20, 40 and 60 minutes. The results revealed that for 60 minutes air-lock dwelling time before measurement, The H escaped as a percentage of total hydrogen concentration is 15.9%, 64%, 136%, 13% for measured ferritic steel, as-supplied ferritic-martensitic steel, H-charged ferritic-martensitic steel, and austenitic steel respectively. The biggest hydrogen escape for all specimen occurred during the first 10 minutes of air-lock dwelling time. To reduce the extensive loss of hydrogen, the temperature of the specimen must be reduced. A vacuum compatible cooling system was built for a new TDS apparatus. The cooling system comprises of A heat sink, cooling loop coupled with a refrigerator and four modules of TE-65-0.6-0.8 micro-thermoelectric coolers (TEC). The cooling system cools to -13.4ºC in 10 minutes at a vacuum pressure of 10-2 mbar.
Prediction of hydrogen concentration responsible for hydrogen-induced mechanical failure in martensitic high-strength steels
(Elsevier Ltd, 2023-02-15) Fangnon, Eric; Malitckii, Evgenii; Latypova, Renata; Vilaça, Pedro; Department of Mechanical Engineering; Materials to Products; University of Oulu
Hydrogen, at critical concentrations, responsible for hydrogen-induced mechanical property degradation cannot yet be estimated beforehand and can only be measured experimentally upon fracture with specific specimen sizes. In this work, we develop two deep learning artificial neural network (ANN) models with the ability to predict hydrogen concentration responsible for early mechanical failure in martensitic ultra-high-strength steels. This family of steels is represented by four different steels encompassing different chemical compositions and heat treatments. The mechanical properties of these steels with varying size and morphology of prior austenitic grains in as-supplied state and after hydrogen-induced failure together with their corresponding hydrogen charging conditions were used as inputs. The feed forward back propagation models with network topologies of 12-7-5-3-2-1 (I) and 14-7-5-3-2-1 (II) were validated and tested with unfamiliar data inputs. The models I and II show good hydrogen concentration prediction capabilities with mean absolute errors of 0.28, and 0.33 wt.ppm at test datasets, respectively. A linear correlation of 80% and 77%, between the experimentally measured and ANN predicted hydrogen concentrations, was obtained for Model I and II respectively. This shows that for this family of steels, the estimation of hydrogen concentration versus property degradation is a feasible approach for material safety analysis.
Review of conventional and advanced non-destructive testing techniques for detection and characterization of small-scale defects
(Elsevier Ltd, 2023-09) Santos Silva, Maria; Malitckii, Evgenii; Santos, Telmo G.; Vilaça, Pedro; Department of Mechanical Engineering; Materials to Products; Universidade Nova de Lisboa
Inspection reliability of small-scale defects, targeting dimensions below 100 µm, is crucial for structural safety of critical components in high-value applications. Early defects are often possible to repair, contributing for the circular economy and sustainability by allowing extended life and reuse of components. During in-service operation, the small-scale defects are typically originated from creep, fatigue, thermal cycles, and environmental damage, or any combination of these multiphysical loading conditions. What are thresholds in Non-Destructive Testing (NDT) techniques to detect and reliably characterise small-scale defects? What is the state of the art of NDT-based solutions, in terms of small-scale defects located at surface, and interior of materials? Examples of small-scale defects in engineering materials are established, and a holistic review is composed on the detectability in terms of sensitivity and resolution. Distinguishable high detection accuracy and resolution is provided by computed tomography paired with computer laminography, scanning thermal microscopy paired with Raman spectroscopy, and NDT techniques paired with machine learning and advanced post-processing signal algorithms. Other promising techniques are time-of-flight diffraction, thermoreflectance thermal imaging, advanced eddy currents probes, like the IOnic probe, micro magnetic bridge probe used in magnetic flux leakage, driven-bacterial cells, Quantum dots and hydrogen-as-a-probe.
Role of retained austenite in hydrogen trapping and hydrogen-assisted fatigue fracture of high-strength steels
(Elsevier Science, 2019-07-08) Malitckii, Evgenii; Yagodzinskyy, Yuriy; Vilaҫa, Pedro; Department of Mechanical Engineering; Advanced Manufacturing and Materials
The 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.
Study of correlation between the steels susceptibility to hydrogen embrittlement and hydrogen thermal desorption spectroscopy using artificial neural network
(Springer London, 2020-09-01) Malitckii, Evgenii; Fangnon, Eric; Vilaca, Pedro; Department of Mechanical Engineering; Advanced Manufacturing and Materials
Steels are the most used structural material in the world, and hydrogen content and localization within the microstructure play an important role in its properties, namely inducing some level of embrittlement. The characterization of the steels susceptibility to hydrogen embrittlement (HE) is a complex task requiring always a broad and multidisciplinary approach. The target of the present work is to introduce the artificial neural network (ANN) computing system to predict the hydrogen-induced mechanical properties degradation using the hydrogen thermal desorption spectroscopy (TDS) data of the studied steel. Hydrogen sensitivity parameter (HSP) calculated from the reduction of elongation to fracture caused by hydrogen was linked to the corresponding hydrogen thermal desorption spectra measured for austenitic, ferritic, and ferritic-martensitic steel grades. Correlation between the TDS input data and HSP output data was studied using two ANN models. A correlation of 98% was obtained between the experimentally measured HSP values and HSP values predicted using the developed densely connected layers ANN model. The performance of the developed ANN models is good even for never-before-seen steels. The ANN-coupled system based on the TDS is a powerful tool in steels characterization especially in the analysis of the steels susceptibility to HE.

Browsing by Author "Malitckii, Evgenii"

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