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Publications (10 of 23) Show all publications
Leach, L., Ågren, J., Höglund, L. & Borgenstam, A. (2019). Diffusion-Controlled Lengthening Rates of Bainitic Ferrite a Part of the Steel Genome. Metallurgical and Materials Transactions. A, 50A(6), 2613-2618
Open this publication in new window or tab >>Diffusion-Controlled Lengthening Rates of Bainitic Ferrite a Part of the Steel Genome
2019 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50A, no 6, p. 2613-2618Article in journal (Refereed) Published
Abstract [en]

As a step in the further development of models and databases to support design of new steels, i.e., the steel genome, the growth of bainitic ferrite plates is accounted for by a thermodynamic and kinetic approach. The thermodynamic aspects are represented by CALPHAD databases and a Gibbs energy barrier for growth B-m. Experimental information on ferrite-plate growth rates for a number of Fe-C alloys, some of high-purity, are analyzed in terms of a modified Zener-Hillert model and the barrier as well as some kinetic parameters are evaluated. It is found that the barrier varies in a smooth way with carbon content and lengthening rate. In order to improve the agreement with the experimental information it was necessary to adjust the diffusion coefficient of carbon in austenite at low temperatures. It is concluded that the representation of the experimental data is satisfactory.

Place, publisher, year, edition, pages
Springer, 2019
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-251697 (URN)10.1007/s11661-019-05208-x (DOI)000466497000008 ()2-s2.0-85064334909 (Scopus ID)
Note

QC 20190520

Available from: 2019-05-20 Created: 2019-05-20 Last updated: 2019-05-29Bibliographically approved
Walbrühl, M., Linder, D., Bonvalet, M., Ågren, J. & Borgenstam, A. (2019). ICME guided property design: Room temperature hardness in cemented carbides. Materials & design, 161, 35-43
Open this publication in new window or tab >>ICME guided property design: Room temperature hardness in cemented carbides
Show others...
2019 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 161, p. 35-43Article in journal (Refereed) Published
Abstract [en]

The potential change in EU regulations may affect the traditional W-C-Co based cemented carbides industry and a methodology is required to accelerate the materials development with alternative binders. This work presents the ICME (Integrated Computational Materials Engineering) framework and the improved models that will enable tailor-made materials design of cemented carbides. The cemented carbide hardness is one of the key properties of the composites and here its close relation to the binder composition is in focus. Modeling the influence of alternative binder materials on the hardness of cemented carbides offers a way to optimize the composite properties of prospective binder candidates virtually, thereby reducing the development time and costs drastically compared to a classical trial-and-error method. The outline of a genetic algorithm is presented and the integration of the required models and tools, that are, or will become, available within this ICME framework, are presented.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
ICME, Hardness, Solubility, Solid solution strengthening, Genetic algorithm
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-240990 (URN)10.1016/j.matdes.2018.11.029 (DOI)000453745400004 ()2-s2.0-85056645666 (Scopus ID)
Note

QC 20190110

Available from: 2019-01-10 Created: 2019-01-10 Last updated: 2019-05-17Bibliographically approved
Bonvalet-Rolland, M., Philippe, T. & Ågren, J. (2019). Kinetic theory of nucleation in multicomponent systems: An application of the thermodynamic extremum principle. Acta Materialia, 171, 1-7
Open this publication in new window or tab >>Kinetic theory of nucleation in multicomponent systems: An application of the thermodynamic extremum principle
2019 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 171, p. 1-7Article in journal (Refereed) Published
Abstract [en]

Nucleation kinetics in a multicomponent supersaturated solid solution is examined. Attachment rate of atoms to a nucleus of a size close to the critical one is determined combining a thermodynamic extremum principle and the Fokker-Planck equation. Two limiting cases are examined; when bulk diffusion controls the nucleation kinetics and when the process is limited by the interfacial mobility. The mixed regime is also treated. Moreover, the growth law in multicomponent alloys is derived in the general case, when both mechanisms are considered. Additionally, the attachment rate is derived, in the classical framework, from a new macroscopic growth equations and the fundamental role of the interfacial mobility is examined. These new general expressions, for the attachment rates and the growth laws, determined either applying the thermodynamic extremum principle or derived from the classical formalism are found to be consistent.

Place, publisher, year, edition, pages
Acta Materialia Inc, 2019
Keywords
Nucleation, Thermodynamics, Kinetics, Extremum principle, Multicomponent
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-254087 (URN)10.1016/j.actamat.2019.03.031 (DOI)000470046400001 ()2-s2.0-85063969944 (Scopus ID)
Note

QC 20190624

Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-06-24Bibliographically approved
Safara, N., Engberg, G. & Ågren, J. (2019). Modeling Microstructure Evolution in a Martensitic Stainless Steel Subjected to Hot Working Using a Physically Based Model. Metallurgical and Materials Transactions. A, 50(3), 1480-1488
Open this publication in new window or tab >>Modeling Microstructure Evolution in a Martensitic Stainless Steel Subjected to Hot Working Using a Physically Based Model
2019 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50, no 3, p. 1480-1488Article in journal (Refereed) Published
Abstract [en]

The microstructure evolution of a martensitic Stainless steel subjected to hot compression is simulated with a physically based model. The model is based on coupled sets of evolution equations for dislocations, vacancies, recrystallization, and grain growth. The advantage of this model is that with only a few experiments, the material-dependent parameters of the model can be calibrated and used for a new alloy in any deformation condition. The experimental data of this work are obtained from a series of hot compression, and subsequent stress relaxation tests performed in a Gleeble thermo-mechanical simulator. These tests are carried out at various temperatures ranging from 900 to 1200 °C, strains up to 0.7, and strain rates of 0.01, 1, and 10 s −1 . The grain growth, flow stress, and stress relaxations are simulated by finding reasonable values for model parameters. The flow stress data obtained at the strain rate of 10 s −1 were used to calibrate the model parameters and the predictions of the model for the lower strain rates were quite satisfactory. An assumption in the model is that the structure of second phase particles does not change during the short time of deformation. The results show a satisfactory agreement between the experimental data and simulated flow stress, as well as less than 5 pct difference for grain growth simulations and predicting the dominant softening mechanisms during stress relaxation according to the strain rates and temperatures under deformation.

Place, publisher, year, edition, pages
Springer, 2019
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-246478 (URN)10.1007/s11661-018-5073-6 (DOI)000457551800036 ()2-s2.0-85058849719 (Scopus ID)
Note

QC 20190319

Available from: 2019-03-19 Created: 2019-03-19 Last updated: 2019-10-17Bibliographically approved
Bonvalet, M., Odqvist, J., Ågren, J. & Forsberg, A. (2019). Modelling of prismatic grain growth in cemented carbides. INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 78, 310-319
Open this publication in new window or tab >>Modelling of prismatic grain growth in cemented carbides
2019 (English)In: INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, ISSN 0263-4368, Vol. 78, p. 310-319Article in journal (Refereed) Published
Abstract [en]

A mean-field model dealing with prismatic grain growth during liquid phase sintering of cemented carbides with a Co-rich binder is presented. The evolution of the size of an assembly of non-spherical grains is obtained using a Kampmann-Wagner approach and by introducing a constant shape factor between the characteristic lengths of prisms. This factor is a function of interfacial energies of the two kind of facets, basal and prismatic, considered. The growth model is based on three different mechanisms, that can be rate limiting, taking place in series: 2D nucleation of a new atomic layer, mass transfer across the interface and long-range diffusion. The driving force for coarsening is distributed between the different facets. These equations are solved numerically, and the simulation results reveal that the specific abnormal grain growth phenomena experimentally observed in cemented carbides may be reproduced with this new more realistic description of the grain shape contrary to the spherical approach developed in the past. It is also shown that the initial powder size distribution, and more specifically its shape has a strong influence on the distribution of the driving force between the different rate limiting mechanisms and thus on the occurrence of abnormal grain growth. In that case, the self-similarity of the normalized grain size distribution over time is not achieved.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2019
Keywords
Grain coarsening, Abnormal grain growth, Cemented carbides, Modelling, Liquid phase sintering
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-239962 (URN)10.1016/j.ijrmhm.2018.10.007 (DOI)000451489300038 ()2-s2.0-85055672266 (Scopus ID)
Funder
VINNOVA
Note

QC 20181211

Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2018-12-11Bibliographically approved
Walbrühl, M., Linder, D., Ågren, J. & Borgenstam, A. (2018). A new hardness model for materials design in cemented carbides. International Journal of Refractory Metals and Hard Materials, 75, 94-100
Open this publication in new window or tab >>A new hardness model for materials design in cemented carbides
2018 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 75, p. 94-100Article in journal (Refereed) Published
Abstract [en]

The Materials Design approach offers new possibilities towards property-oriented materials development. The performance of cemented carbides is significantly influenced by properties like the hardness and fracture toughness. Fundamentally based phenomenological models, which allow for prediction of the properties of interest, make it possible to tailor the properties of the material based on the required performance. None of the previously available models are suitable to actively design the cemented carbide hardness because they are valid only for Co binders and do not allow alternative binder phases. The hardness is greatly influenced by the chemistry, binder volume fraction and carbide grain size. Only the chemistry, specifically the binder composition, leaves the possibility to optimize the binder hardness and to exceed classical WC-Co cemented carbides. Specifically focusing on the design of the binder phase, a new binder hardness description is implemented in a modified Engqvist hardness model and allows description of a wider range of conventional and alternative systems. The model was validated for various published cemented carbide systems and is able to predict their hardness within a 10% error. The assessed systems contain classical Co binders as well as alternative, austenitic binders based on Fe, Ni and Co.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Alternative binder, Cemented carbides, ICME, Materials design, Solid solution strengthening, Thermo-Calc
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-227506 (URN)10.1016/j.ijrmhm.2018.04.004 (DOI)000437362100013 ()2-s2.0-85045428618 (Scopus ID)
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-07-23Bibliographically approved
Lu, S., Ågren, J. & Vitos, L. (2018). Ab initio study of energetics and structures of heterophase interfaces: From coherent to semicoherent interfaces. Acta Materialia, 156, 20-30
Open this publication in new window or tab >>Ab initio study of energetics and structures of heterophase interfaces: From coherent to semicoherent interfaces
2018 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 156, p. 20-30Article in journal (Refereed) Published
Abstract [en]

Density functional theory calculations have been performed to study the structures and energetics of coherent and semicoherent TiC/Fe interfaces. A systematic method for determining the interfacial energy of the semicoherent interface with misfit dislocation network has been developed. The obtained interfacial energies are used to evaluate the aspect ratio for the plate-like precipitate and a quantitative agreement with the experimental results is reached. Based on the obtained interfacial energies and atomic structure details, we propose two scenarios for heterogeneous nucleation on an edge dislocation, shedding light on the thermodynamics of precipitate nucleation and growth. The present method can be easily applied to any heterophase interfaces between metals and oxides/carbides/nitrides. 

Place, publisher, year, edition, pages
Pergamon Press, 2018
Keywords
Steels, Transition metal carbides, Heterophase interface, Interfacial energy, ab initio calculation
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-234584 (URN)10.1016/j.actamat.2018.06.030 (DOI)000442062800003 ()2-s2.0-85048928839 (Scopus ID)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Swedish Research CouncilSwedish Foundation for Strategic Research
Note

QC 20180914

Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2018-09-14Bibliographically approved
Walbrühl, M., Linder, D., Ågren, J. & Borgenstam, A. (2018). Alternative Ni-based cemented carbide binder – Hardness characterization by nano-indentation and focused ion beam. International Journal of Refractory Metals and Hard Materials, 73, 204-209
Open this publication in new window or tab >>Alternative Ni-based cemented carbide binder – Hardness characterization by nano-indentation and focused ion beam
2018 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 73, p. 204-209Article in journal (Refereed) Published
Abstract [en]

The nano-hardness in the alternative 85Ni-15Fe binder phase of WC cemented carbide has been investigated. High-resolution scanning electron microscopy (SEM) imaging was used to measure the projected indentation area and a general pile-up correction, confirmed on selected indents, has been employed using atomic force microscopy (AFM). Focused ion-beam (FIB) cross-sections have been used to investigate the binder morphology below the indentations and the local binder hardness has been associated to the distance to the surrounding WC grains. Generally, decreasing distance to the WC grains leads to increased binder hardness. Furthermore, the nano-hardness for the cemented carbide binder has been corrected for the indentation size effect (ISE) to obtain the corresponding macroscopic hardness. A solid solution strengthening model for multicomponent bulk alloys was used to calculate the expected binder Vickers hardness considering the binder solubilities of W and C. Both the strengthening model and the ISE corrected hardness values, for larger binder regions, are in good agreement indicating that the intrinsic binder phase hardness is similar to that of a bulk metal alloy with similar composition.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Alternative binder hardness, Binder shape, Cemented carbides, Constrained binder, Indentation size effect
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-227554 (URN)10.1016/j.ijrmhm.2018.02.017 (DOI)000430028800027 ()2-s2.0-85042350653 (Scopus ID)
Funder
VINNOVA
Note

QC 20180516

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2018-05-16Bibliographically approved
Barkar, T., Höglund, L., Odqvist, J. & Ågren, J. (2018). Effect of concentration dependent gradient energy coefficient on spinodal decomposition in the Fe-Cr system. Computational materials science, 143, 446-453
Open this publication in new window or tab >>Effect of concentration dependent gradient energy coefficient on spinodal decomposition in the Fe-Cr system
2018 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 143, p. 446-453Article in journal (Refereed) Published
Abstract [en]

The Cahn–Hilliard equation is solved with thermodynamic and kinetic input, using the Thermo-Calc and DICTRA software packages rather than simpler models e.g. regular solution. A concentration dependent expression for the gradient energy coefficient is introduced and its effect on simulated decomposition is discussed. Simulations were carried out in 2D and 3D using the FiPy software package modified for non-linear problems.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Computational Mathematics
Identifiers
urn:nbn:se:kth:diva-219887 (URN)10.1016/j.commatsci.2017.11.043 (DOI)000424900000053 ()2-s2.0-85036461179 (Scopus ID)
Funder
VINNOVA
Note

QC 20171215

Available from: 2017-12-15 Created: 2017-12-15 Last updated: 2018-09-25Bibliographically approved
Walbrühl, M., Ågren, J., Blomqvist, A. & Larsson, H. (2018). ICME guided modeling of surface gradient formation in cemented carbides. International Journal of Refractory Metals and Hard Materials, 72, 33-38
Open this publication in new window or tab >>ICME guided modeling of surface gradient formation in cemented carbides
2018 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 72, p. 33-38Article in journal (Refereed) Published
Abstract [en]

Structural gradients are of great interest for state-of-the-art cemented carbides used in metal cutting applications. The gradient growth during sintering is controlled by the fundamental aspects of diffusion, thermodynamics and phase equilibria in systems with multiple components and phases. With the demand for binder alternatives to Co, there is a need for understanding the diffusion and thermodynamics in new materials systems. Materials development guided by ICME (Integrated Computational Materials Engineering) is a new approach that accelerates the design of tailor-made materials, assisting us to find and optimize prospective binder candidates using computational tools. The role of the thermodynamic descriptions will be briefly discussed but this work focuses on a better kinetic description. Models based on cemented carbide microstructures and fundamental understanding of kinetics will allow for a more general use of simulations of gradient formation. The diffusion of elements during sintering mainly occurs in the liquid binder phase, with the solid WC and gamma phases acting as an effective labyrinth, hindering diffusion. In this work, the liquid mobilities and the effective labyrinth factor is studied for traditional and alternative binders by combing ab initio molecular dynamics and diffusion couple experiments with CALPHAD modeling. 

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
AIMD, DICTRA, ICME, Labyrinth factor, Liquid diffusion, Surface gradients, Bins, Carbide tools, Carbides, Diffusion, Liquids, Metal cutting, Molecular dynamics, Phase equilibria, Sintering, Thermodynamics, Binders
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-223113 (URN)10.1016/j.ijrmhm.2017.12.010 (DOI)000427209100006 ()2-s2.0-85038021984 (Scopus ID)
Note

Export Date: 13 February 2018; Article; CODEN: IJRMD; Correspondence Address: Walbrühl, M.; Department of Materials Science and Engineering, Royal Institute of TechnologySweden; email: walbruhl@kth.se; Funding details: KTH, Kungliga Tekniska Högskolan; Funding details: VINNOVA. QC 20180227

Available from: 2018-02-27 Created: 2018-02-27 Last updated: 2018-05-24Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-4521-6089

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