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Bjerkén, Christina, PhDORCID iD iconorcid.org/0000-0002-7952-5330
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Publications (10 of 66) Show all publications
Krause, A. M., Olsson, P. A., Music, D. & Bjerkén, C. (2023). Interstitial diffusion of hydrogen in M7C3 (M=Cr,Mn,Fe). Computational materials science, 218, Article ID 111940.
Open this publication in new window or tab >>Interstitial diffusion of hydrogen in M7C3 (M=Cr,Mn,Fe)
2023 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 218, article id 111940Article in journal (Refereed) Published
Abstract [en]

To increase the understanding of the role of carbide precipitates on the hydrogen embrittlement of martensitic steels, we have performed a density functional theory study on the solution energies and energy barriers for hydrogen diffusion in orthorhombic M7C3 (M = Cr, Mn, Fe). Hydrogen can easily diffuse into the lattice and cause internal stresses or bond weakening, which may promote reduced ductility. Solution energies of hydrogen at different lattice positions have systematically been explored, and the lowest values are -0.28, 0.00, and 0.03 eV/H-atom for Cr7C3, Mn7C3, and Fe7C3, respectively. Energy barriers for the diffusion of hydrogen atoms have been probed with the nudged elastic band method, which shows comparably low barriers for transport via interstitial octahedral sites for all three systems. Analysis of the atomic volume reveals a correlation between low solution energies and energy barriers and atoms with large atomic volumes. Furthermore, it shows that the presence of carbon tends to increase the energy barrier. Our results can explain previous experimental findings of hydrogen located in the bulk of CrC precipitates and provide a solid basis for future design efforts of steels with high strength and commensurable ductility.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Hydrogen embrittlement, Hydrogen diffusion, Carbides, Density functional theory, Nudged elastic band method
National Category
Condensed Matter Physics Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:mau:diva-56883 (URN)10.1016/j.commatsci.2022.111940 (DOI)000910929000001 ()2-s2.0-85144276997 (Scopus ID)
Funder
Vinnova, 2020-03115
Available from: 2022-12-22 Created: 2022-12-22 Last updated: 2023-08-15Bibliographically approved
Nigro, C. F., Bjerkén, C. & Mellbin, Y. (2021). Phase-field modelling: effect of an interface crack on precipitation kinetics in a multi-phase microstructure. International Journal of Fracture, 227, 219-241
Open this publication in new window or tab >>Phase-field modelling: effect of an interface crack on precipitation kinetics in a multi-phase microstructure
2021 (English)In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 227, p. 219-241Article in journal (Refereed) Published
Abstract [en]

Premature failures in metals can arise from the local reduction of the fracture toughness when brittle phases precipitate. Precipitation can be enhanced at the grain and phase boundaries and be promoted by stress concentration causing a shift of the terminal solid solubility. This paper provides the description of a model to predict stress-induced precipitation along phase interfaces in one-phase and two-phase metals. A phase-field approach is employed to describe the microstructural evolution. The combination between the system expansion caused by phase transformation, the stress field and the energy of the phase boundary is included in the model as the driving force for precipitate growth. In this study, the stress induced by an opening interface crack is modelled through the use of linear elastic fracture mechanics and the phase boundary energy by a single parameter in the Landau potential. The results of the simulations for a hydrogenated (α+β) titanium alloy display the formation of a precipitate, which overall decelerates in time. Outside the phase boundary, the precipitate mainly grows by following the isostress contours. In the phase boundary, the hydride grows faster and is elongated. Between the phase boundary and its surrounding, the matrix/hydride interface is smoothened. The present approach allows capturing crack-induced precipitation at phase interfaces with numerical efficiency by solving one equation only. The present model can be applied to other multi-phase metals and precipitates through the use of their physical properties and can also contribute to the efficiency of multi-scale crack propagation schemes.

Place, publisher, year, edition, pages
Springer Nature, 2021
Keywords
Interface crack; Phase boundary; Phase transformation; Phase-field method; Precipitation kinetics; Multi-phase
National Category
Materials Engineering
Identifiers
urn:nbn:se:mau:diva-37632 (URN)10.1007/s10704-020-00510-x (DOI)000608389500001 ()2-s2.0-85100154357 (Scopus ID)
Available from: 2020-12-17 Created: 2020-12-17 Last updated: 2024-02-05Bibliographically approved
Nigro, C. F., Bjerkén, C. & Mellbin, Y. (2020). Modeling of a Crack-induced Hydride Formation at a Grain Boundary in Metals. International Journal of Offshore and Polar Engineering, 30(4), 478-486, Article ID ISOPE-20-30-4-478.
Open this publication in new window or tab >>Modeling of a Crack-induced Hydride Formation at a Grain Boundary in Metals
2020 (English)In: International Journal of Offshore and Polar Engineering, ISSN 1053-5381, Vol. 30, no 4, p. 478-486, article id ISOPE-20-30-4-478Article in journal (Refereed) Published
Abstract [en]

Crack-induced hydride formation can occur in specific metallic structures, reducing their mechanical properties and facilitating failure. Grain boundaries are observed to be preferential sites for hydride formation. We present a phasefield approach describing the kinetics of crack-induced hydride formation at a grain boundary, by using the Allen-Cahn formulation and including the increase in grain boundary energy. Hydride development is found to occur at the crack tip and in the grain boundary. These regions seemingly evolve independently, except when the crack is very close to or lies in the grain boundary. 

Place, publisher, year, edition, pages
International Society of Offshore & Polar Engineers, 2020
Keywords
Allen-Cahn formulation, hydride precipitation, phase transformation, mode I crack, phasefield method, grain boundary, Hydrogen embrittlement
National Category
Materials Engineering
Identifiers
urn:nbn:se:mau:diva-37578 (URN)10.17736/ijope.2020.oa24 (DOI)000599526300012 ()2-s2.0-85098856544 (Scopus ID)
Available from: 2020-12-15 Created: 2020-12-15 Last updated: 2024-02-05Bibliographically approved
Nigro, C. F., Bjerkén, C. & Mellbin, Y. (2019). Modelling of a Crack-Induced Hydride Formation near a Phase Boundary in Metals. In: the International Society of Offshore and Polar Engineers (ISOPE) (Ed.), Proceedings of the Twenty-ninth (2019) International Ocean and Polar Engineering Conference: . Paper presented at Twenty-ninth (2019) International Ocean and Polar Engineering Conference  (pp. 4186-4194). International Society of Offshore & Polar Engineers
Open this publication in new window or tab >>Modelling of a Crack-Induced Hydride Formation near a Phase Boundary in Metals
2019 (English)In: Proceedings of the Twenty-ninth (2019) International Ocean and Polar Engineering Conference / [ed] the International Society of Offshore and Polar Engineers (ISOPE), International Society of Offshore & Polar Engineers, 2019, p. 4186-4194Conference paper, Published paper (Refereed)
Abstract [en]

In presence of hydrogen, crack-induced hydride formation can occur in specific metallic structures, reduce their mechanical properties and facilitate failure. Phase boundaries have been observed to be preferential site for hydride formation. The inevitable presence of both cracks and phase boundaries is consequently a threat for these metals. This paper presents a phase field approach describing hydride formation induced by a crack lying near a grain boundary, by using Allen-Cahn’s formulation associated with linear elastic fracture mechanics. The analysis of the results reveals an enhancement of crack-induced hydride development in the proximity of a grain boundary.

Place, publisher, year, edition, pages
International Society of Offshore & Polar Engineers, 2019
Keywords
hydrogen embrittlement, phase transformation, phasefield method, Allen-Cahn formulation, hydride precipitation, mode I crack, grain boundary
National Category
Materials Engineering
Identifiers
urn:nbn:se:mau:diva-37575 (URN)2-s2.0-85079798792 (Scopus ID)9781880653852 (ISBN)
Conference
Twenty-ninth (2019) International Ocean and Polar Engineering Conference 
Available from: 2020-12-14 Created: 2020-12-14 Last updated: 2023-12-19Bibliographically approved
Maimaitiyili, T., Woracek, R., Neikter, M., Boin, M., Wimpory, R. C., Pederson, R., . . . Bjerkén, C. (2019). Residual Lattice Strain and Phase Distribution in Ti-6Al-4V Produced by Electron Beam Melting (ed.). Materials, 12(4), Article ID 667.
Open this publication in new window or tab >>Residual Lattice Strain and Phase Distribution in Ti-6Al-4V Produced by Electron Beam Melting
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2019 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 4, article id 667Article in journal (Refereed) Published
Abstract [en]

Residual stress/strain and microstructure used in additively manufactured material are strongly dependent on process parameter combination. With the aim to better understand and correlate process parameters used in electron beam melting (EBM) of Ti-6Al-4V with resulting phase distributions and residual stress/strains, extensive experimental work has been performed. A large number of polycrystalline Ti-6Al-4V specimens were produced with different optimized EBM process parameter combinations. These specimens were post-sequentially studied by using high-energy X-ray and neutron diffraction. In addition, visible light microscopy, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) studies were performed and linked to the other findings. Results show that the influence of scan speed and offset focus on resulting residual strain in a fully dense sample was not significant. In contrast to some previous literature, a uniform α- and β-Ti phase distribution was found in all investigated specimens. Furthermore, no strong strain variations along the build direction with respect to the deposition were found. The magnitude of strain in α and β phase show some variations both in the build plane and along the build direction, which seemed to correlate with the size of the primary β grains. However, no relation was found between measured residual strains in α and β phase. Large primary β grains and texture appear to have a strong effect on X-ray based stress results with relatively small beam size, therefore it is suggested to use a large beam for representative bulk measurements and also to consider the prior β grain size in experimental planning, as well as for mathematical modelling.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
residual stress/strain, electron beam melting, diffraction, Ti-6Al-4V, electron backscattered diffraction, X-ray diffraction
National Category
Engineering and Technology
Identifiers
urn:nbn:se:mau:diva-2731 (URN)10.3390/ma12040667 (DOI)000460793300117 ()30813435 (PubMedID)28447 (Local ID)28447 (Archive number)28447 (OAI)
Available from: 2020-02-27 Created: 2020-02-27 Last updated: 2022-04-26Bibliographically approved
Neikter, M., Woracek, R., Maimaitiyili, T., Scheffzük, C., Strobl, M., Antti, M.-L., . . . Bjerkén, C. (2018). Alpha texture variations in additive manufactured Ti-6Al-4V investigated with neutron diffraction (ed.). Additive Manufacturing, 23, 225-234
Open this publication in new window or tab >>Alpha texture variations in additive manufactured Ti-6Al-4V investigated with neutron diffraction
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2018 (English)In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 23, p. 225-234Article in journal (Refereed) Published
Abstract [en]

Variation of texture in Ti-6Al-4V samples produced by three different additive manufacturing (AM) processes has been studied by neutron time-of-flight (TOF) diffraction. The investigated AM processes were electron beam melting (EBM), selective laser melting (SLM) and laser metal wire deposition (LMwD). Additionally, for the LMwD material separate measurements were done on samples from the top and bottom pieces in order to detect potential texture variations between areas close to and distant from the supporting substrate in the manufacturing process. Electron backscattered diffraction (EBSD) was also performed on material parallel and perpendicular to the build direction to characterize the microstructure. Understanding the context of texture for AM processes is of significant relevance as texture can be linked to anisotropic mechanical behavior. It was found that LMwD had the strongest texture while the two powder bed fusion (PBF) processes EBM and SLM displayed comparatively weaker texture. The texture of EBM and SLM was of the same order of magnitude. These results correlate well with previous microstructural studies. Additionally, texture variations were found in the LMwD sample, where the part closest to the substrate featured stronger texture than the corresponding top part. The crystal direction of the α phase with the strongest texture component was [112¯3].

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Neutron time-of-flight diffraction, SKAT, Texture, Ti-6Al-4V, Additive manufacturing
National Category
Engineering and Technology
Identifiers
urn:nbn:se:mau:diva-2439 (URN)10.1016/j.addma.2018.08.018 (DOI)000453495500022 ()2-s2.0-85051782355 (Scopus ID)28438 (Local ID)28438 (Archive number)28438 (OAI)
Available from: 2020-02-27 Created: 2020-02-27 Last updated: 2024-02-06Bibliographically approved
Ehrlin, N., Fisk, M. & Bjerkén, C. (2018). Flow stress model for hydrogen degraded Inconel 718 (ed.). Mechanics of materials, 119, 56-64
Open this publication in new window or tab >>Flow stress model for hydrogen degraded Inconel 718
2018 (English)In: Mechanics of materials, ISSN 0167-6636, E-ISSN 1872-7743, Vol. 119, p. 56-64Article in journal (Refereed) Published
Abstract [en]

For life time estimation, it is desirable to capture the lowering of yield strength and premature failure that some alloys exhibits when subjected to hydrogen. For this, a mechanism based material model has been developed to simulate the hydrogen enhanced localized plasticity (HELP) for the superalloy IN718. The model accounts for the increase in mobility of moving dislocations during plastic deformation, whenever hydrogen is present in the material. Tensile tests performed at four different strain rates: 5 x 10(-5), 5 x 10(-4), 5 x 10(-3) and 5 x 10(-2) s(-1) show a difference in yield behaviour between hydrogen pre-charged and uncharged samples. No strain rate dependency of the hydrogen effect could be concluded. Two different hydrogen charging methods have been used: cathodic charging with molten salt as electrolyte, and high temperature gas charging. No differences in the tensile response could be seen between the two different charging methods. The proposed model was fitted against the experimental curves using a minimizing method and model parameters were obtained. Comprising iteratively updated parameters, the model is suited for implementation in finite element software.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Materials Science, Multidisciplinary, Mechanics
National Category
Engineering and Technology
Identifiers
urn:nbn:se:mau:diva-2380 (URN)10.1016/j.mechmat.2018.01.007 (DOI)000428493500007 ()2-s2.0-85041929915 (Scopus ID)27288 (Local ID)27288 (Archive number)27288 (OAI)
Available from: 2020-02-27 Created: 2020-02-27 Last updated: 2024-01-17Bibliographically approved
Nigro, C. F., Bjerkén, C. & Olsson, P. A. (2018). Phase structural ordering kinetics of second-phase formation in the vicinity of a crack (ed.). International Journal of Fracture, 209(1-2), 91-107
Open this publication in new window or tab >>Phase structural ordering kinetics of second-phase formation in the vicinity of a crack
2018 (English)In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 209, no 1-2, p. 91-107Article in journal (Refereed) Published
Abstract [en]

The formation of a second phase in presence of a crack in a crystalline material is modelled and studied for different prevailing conditions in order to predict and a posteriori prevent failure, e.g. by delayed hydride cracking. To this end, the phase field formulation of Ginzburg-Landau is selected to describe the phase transformation, and simulations using the finite volume method are performed for a wide range of material properties. A sixth order Landau potential for a single structural order parameter is adopted because it allows the modeling of both first and second order transitions and its corresponding phase diagram can be outlined analytically. The elastic stress field induced by the crack is found to cause a space-dependent shift in the transition temperature, which promotes a second-phase precipitation in vicinity of the crack tip. The spatio-temporal evolution during nucleation and growth is successfully monitored for different combinations of material properties and applied loads. Results for the second-phase shape and size evolution are presented and discussed for a number of selected characteristic cases. The numerical results at steady state are compared to mean-field equilibrium solutions and a good agreement is achieved. For materials applicable to the model, the results can be used to predict the evolution of an eventual second-phase formation through a dimensionless phase transformation in the crack-tip vicinity for given conditions.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Phase transformation, Mode I Crack, Phase field method, Ginzburg-Landau formulation, Precipitation kinetics
National Category
Engineering and Technology
Identifiers
urn:nbn:se:mau:diva-2706 (URN)10.1007/s10704-017-0242-y (DOI)000423710000006 ()2-s2.0-85027979140 (Scopus ID)23762 (Local ID)23762 (Archive number)23762 (OAI)
Available from: 2020-02-27 Created: 2020-02-27 Last updated: 2024-02-05Bibliographically approved
Ehrlin, N., Fisk, M. & Bjerkén, C. (2017). Flow stress model for hydrogen degraded Inconel 718 (ed.). In: (Ed.), Emmanuel E. Gdoutos (Ed.), ICF 2017 - 14th International Conference on Fracture, Vol 1: . Paper presented at 2017 14th International Conference on Fracture, ICF 2017, Rhodes, Greece, 18-20 June 2017 (pp. 233-234). International Conference on Fracture
Open this publication in new window or tab >>Flow stress model for hydrogen degraded Inconel 718
2017 (English)In: ICF 2017 - 14th International Conference on Fracture, Vol 1 / [ed] Emmanuel E. Gdoutos, International Conference on Fracture , 2017, p. 233-234Conference paper, Published paper (Refereed)
Abstract [en]

A mechanism based material model has been developed to simulate hydrogen enhanced localized plasticity for superalloy IN718 in the present work. The model accounts for the increase in mobility of the moving dislocation during plastic deformation, whenever exposed for hydrogen. Two different hydrogen charging methods have been used: cathodic charging with molten salt as electrolyte, and high temperature gas chamber charging. Tensile tests performed at a strain rate of 5×10−5 s-1 show a clear difference between charged samples and uncharged samples. No or small differences could be seen between the two different charging methods. The material model was fitted against the experimental curves using a minimising method alternating fitting parameters. The agreement between the experimental value and the model was good.

Place, publisher, year, edition, pages
International Conference on Fracture, 2017
National Category
Engineering and Technology
Identifiers
urn:nbn:se:mau:diva-65033 (URN)2-s2.0-85065964061 (Scopus ID)978-1-5108-7848-8 (ISBN)
Conference
2017 14th International Conference on Fracture, ICF 2017, Rhodes, Greece, 18-20 June 2017
Available from: 2024-01-16 Created: 2024-01-16 Last updated: 2024-01-16Bibliographically approved
Maimaitiyili, T., Woracek, R., Bjerkén, C., Strobl, M. & Schäfer, N. (2017). Fracture mechanical studies of additive manufactured Ti6Al4V by synchrotron X-ray diffraction. In: Emmanuel E. Gdoutos (Ed.), ICF 2017 - 14th International Conference on Fracture, Vol 1: . Paper presented at 2017 14th International Conference on Fracture, ICF 2017, Rhodes, Greece, 18-20 June 2017 (pp. 253-254). International Conference on Fracture, 1
Open this publication in new window or tab >>Fracture mechanical studies of additive manufactured Ti6Al4V by synchrotron X-ray diffraction
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2017 (English)In: ICF 2017 - 14th International Conference on Fracture, Vol 1 / [ed] Emmanuel E. Gdoutos, International Conference on Fracture , 2017, Vol. 1, p. 253-254Conference paper, Published paper (Refereed)
Abstract [en]

Better understanding of the formation and distribution of hydrides, elastic and plastic strains in deformed polycrystalline, multiphase materials such as digitally manufactured Ti-6Al-4V is important for structural engineering. Polycrystalline Ti-6Al4V alloy samples produced by additive manufacturing techniques called electron beam melting (EBM) have been studied at third generation, high energy synchrotron X-Ray diffraction beam line with energy dispersive X-Ray diffraction setup. The elastic strain in the as built and hydrogenated material determined by extracting unit cell parameters of the existing phases in the system by using whole pattern analysis method Rietveld and Pawley. © 2017 ICF 2017 - 14th International Conference on Fracture. All rights reserved.

Place, publisher, year, edition, pages
International Conference on Fracture, 2017
Keywords
3D printers, Additives, Aluminum alloys, Fracture, Polycrystalline materials, Strain, Synchrotron radiation, Ternary alloys, Vanadium alloys, X ray diffraction, Energy dispersive x-ray diffractions, High-energy synchrotron X-rays, Hydrogenated materials, Manufacturing techniques, Mechanical study, Multiphase materials, Synchrotron x ray diffraction, Unit cell parameters, Titanium alloys
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:mau:diva-64886 (URN)2-s2.0-85065993265 (Scopus ID)978-1-5108-7848-8 (ISBN)
Conference
2017 14th International Conference on Fracture, ICF 2017, Rhodes, Greece, 18-20 June 2017
Available from: 2024-01-08 Created: 2024-01-08 Last updated: 2024-01-08Bibliographically approved
Projects
Phase field modeling; Malmö University
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7952-5330

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