John Ågren - Academia.edu (original) (raw)
Papers by John Ågren
Acta Materialia, 2002
A newly constructed computer program was used to simulate partitionless growth of alpha in gamma ... more A newly constructed computer program was used to simulate partitionless growth of alpha in gamma of Fe-Ni-C alloys, taking into account so-called solute drag by evaluating the dissipation of Gibbs energy due to diffusion inside the interface and in the nickel spike being pushed in front of it. It could be shown how the conditions at the alpha/gamma interface vary with the velocity. A continuous change from paraequilibrium to quasi-paraconditions could be illustrated in the phase diagram. By combination with an approximate analytical growth equation, it was possible to derive the thickness of a as function of time. The growth velocity was assumed to start at very high values but decreased due to the pile-up of carbon. For alloy compositions outside the limit for quasi-paraconditions and just inside it the growth was predicted to stop suddenly when critical conditions are approached during the reaction. For alloy compositions further inside the limit, there was no such stop, except by...
In cemented carbides the effective diffusivities are associated with the carbides acting as obsta... more In cemented carbides the effective diffusivities are associated with the carbides acting as obstacles that increase the diffusion distance, thus altering the overall diffusion in the composite. Fro ...
We have developed Ti-Zr-Cu-Pd-Sn bulk metallic glass without toxic elements which exhibits distin... more We have developed Ti-Zr-Cu-Pd-Sn bulk metallic glass without toxic elements which exhibits distinct plasticity (~12.6%) by revealing strain hardening before failure. Specimens performed under compr ...
International Journal of Refractory Metals and Hard Materials, 2018
International Journal of Refractory Metals and Hard Materials, 2018
Materials & Design, 2018
Computational Materials Science, 2018
HTM Journal of Heat Treatment and Materials, 2017
Carbonitriding and internal oxidation have been simulated simultaneously using the DICTRA homogen... more Carbonitriding and internal oxidation have been simulated simultaneously using the DICTRA homogenization model. The predicted carbon and nitrogen profiles as well as the oxide and nitride phase fraction profiles agree favourably with experimental data obtained from the literature, though some discrepancies exist. The present approach should be a very useful tool in process control and optimization.
Materials and Corrosion, 2016
Pure iron has been oxidized at 600 °C and 1 bar in dry O2 (oxygen partial pressure 0.05, bal. N2)... more Pure iron has been oxidized at 600 °C and 1 bar in dry O2 (oxygen partial pressure 0.05, bal. N2) and the mass gain as well as the thicknesses of the individual oxide phases have been measured. The oxidation process has been simulated using a modified version of the homogenization model as implemented in Dictra; this has helped to rationalize the kinetics of oxide scale formation and in particular the evolution of the hematite (Fe2O3), magnetite (Fe3O4), and wustite (FeO) which form. Independently assessed thermodynamic and kinetic Calphad databases are needed for the calculations; details of these are given. Reasonable agreement between simulation results and experimental data is obtained, though it is concluded that the large influence of grain boundary diffusion on the oxidation rate needs further consideration.
Materials Science and Engineering: A, 2017
International Journal of Refractory Metals and Hard Materials, 2017
![Research paper thumbnail of [O33] Application of compound-energy formalism to the parabolic growth of solid metal oxides](https://attachments.academia-assets.com/117227722/thumbnails/1.jpg)
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Bearing Steels: Into the 21st Century
The present paper is a review of recent results on simulation of heat treatment response of beari... more The present paper is a review of recent results on simulation of heat treatment response of bearing steels. Two aspects are considered namely firstly the evolution of the microstructure during heat treatment, especially the carbide structure and the corresponding distribution of alloying elements in the austenite around the carbides. This information is important in order to understand the hardening response of the steel. The analysis is based on thermodynamics and kinetics of multi component systems. Both single carbide sizes and realistic size distributions are considered. Secondly the evolution of the residual stresses and the distortion is considered during the full heat treatment cycle including heating and cooling. These latter simulations focus on the behavior of full components. Special interest is devoted to origins of out of roundness of bearing rings. Factors like original geometrical imperfections, residual stresses from mechanical manufacturing steps, segregation and uneven cooling action during quenching are considered.
Computational materials design for lightweight steels with ICME approach: thermodynamics and prec... more Computational materials design for lightweight steels with ICME approach: thermodynamics and precipitation strengthening simulation
Journal of Alloys and Compounds, 2018
IEEE Transactions on Magnetics, 2014
Optically highly transparent, soft magnetic thin films (4-18 nm thick) of Fe-B-Nb and Fe-B-Nb-Y-b... more Optically highly transparent, soft magnetic thin films (4-18 nm thick) of Fe-B-Nb and Fe-B-Nb-Y-based glassy metal targets were grown on quartz substrates by pulsed laser deposition, and their optical and magneto-optical properties were investigated over the visible spectrum (400-700 nm). All the films found to be fully amorphous in structure were continuous with uniform thickness and surface morphology. Their optical transmittance in the range 50%-85% was found to be film thickness dependent over the entire visible regime. The Verdet constant (V) and Faraday rotation angle (θf ) for different films (~4-18 nm) investigated as a function of wavelength (λ) show considerably higher values for the films of Fe-B-Nb-Y alloy as compared with those for Fe-B-Nb films, e.g., the ~4 nm film of Fe-B-Nb-Y alloy exhibits V ~ 49°/Oe cm and θf ~ 26°/μm while it decreased to ~29.4°/Oe and ~11.8°/μm, respectively, for the Fe-B-Nb alloy at λ = 611 nm. A linear relationship is found for the wavelength dependence of V and θf for both alloy systems. To the best of our knowledge, these values are considerably higher than those reported for any other magneto-optic material. The films are found to be soft magnetic with a high saturation moment while their magnetic coercivity values increases with thinness of the films. The observed combination of optical and magneto-optical properties of this new class of amorphous metallic films makes them viable for multifunctional magneto-optical applications.
Acta Materialia, 2002
A newly constructed computer program was used to simulate partitionless growth of alpha in gamma ... more A newly constructed computer program was used to simulate partitionless growth of alpha in gamma of Fe-Ni-C alloys, taking into account so-called solute drag by evaluating the dissipation of Gibbs energy due to diffusion inside the interface and in the nickel spike being pushed in front of it. It could be shown how the conditions at the alpha/gamma interface vary with the velocity. A continuous change from paraequilibrium to quasi-paraconditions could be illustrated in the phase diagram. By combination with an approximate analytical growth equation, it was possible to derive the thickness of a as function of time. The growth velocity was assumed to start at very high values but decreased due to the pile-up of carbon. For alloy compositions outside the limit for quasi-paraconditions and just inside it the growth was predicted to stop suddenly when critical conditions are approached during the reaction. For alloy compositions further inside the limit, there was no such stop, except by...
In cemented carbides the effective diffusivities are associated with the carbides acting as obsta... more In cemented carbides the effective diffusivities are associated with the carbides acting as obstacles that increase the diffusion distance, thus altering the overall diffusion in the composite. Fro ...
We have developed Ti-Zr-Cu-Pd-Sn bulk metallic glass without toxic elements which exhibits distin... more We have developed Ti-Zr-Cu-Pd-Sn bulk metallic glass without toxic elements which exhibits distinct plasticity (~12.6%) by revealing strain hardening before failure. Specimens performed under compr ...
International Journal of Refractory Metals and Hard Materials, 2018
International Journal of Refractory Metals and Hard Materials, 2018
Materials & Design, 2018
Computational Materials Science, 2018
HTM Journal of Heat Treatment and Materials, 2017
Carbonitriding and internal oxidation have been simulated simultaneously using the DICTRA homogen... more Carbonitriding and internal oxidation have been simulated simultaneously using the DICTRA homogenization model. The predicted carbon and nitrogen profiles as well as the oxide and nitride phase fraction profiles agree favourably with experimental data obtained from the literature, though some discrepancies exist. The present approach should be a very useful tool in process control and optimization.
Materials and Corrosion, 2016
Pure iron has been oxidized at 600 °C and 1 bar in dry O2 (oxygen partial pressure 0.05, bal. N2)... more Pure iron has been oxidized at 600 °C and 1 bar in dry O2 (oxygen partial pressure 0.05, bal. N2) and the mass gain as well as the thicknesses of the individual oxide phases have been measured. The oxidation process has been simulated using a modified version of the homogenization model as implemented in Dictra; this has helped to rationalize the kinetics of oxide scale formation and in particular the evolution of the hematite (Fe2O3), magnetite (Fe3O4), and wustite (FeO) which form. Independently assessed thermodynamic and kinetic Calphad databases are needed for the calculations; details of these are given. Reasonable agreement between simulation results and experimental data is obtained, though it is concluded that the large influence of grain boundary diffusion on the oxidation rate needs further consideration.
Materials Science and Engineering: A, 2017
International Journal of Refractory Metals and Hard Materials, 2017
Bearing Steels: Into the 21st Century
The present paper is a review of recent results on simulation of heat treatment response of beari... more The present paper is a review of recent results on simulation of heat treatment response of bearing steels. Two aspects are considered namely firstly the evolution of the microstructure during heat treatment, especially the carbide structure and the corresponding distribution of alloying elements in the austenite around the carbides. This information is important in order to understand the hardening response of the steel. The analysis is based on thermodynamics and kinetics of multi component systems. Both single carbide sizes and realistic size distributions are considered. Secondly the evolution of the residual stresses and the distortion is considered during the full heat treatment cycle including heating and cooling. These latter simulations focus on the behavior of full components. Special interest is devoted to origins of out of roundness of bearing rings. Factors like original geometrical imperfections, residual stresses from mechanical manufacturing steps, segregation and uneven cooling action during quenching are considered.
Computational materials design for lightweight steels with ICME approach: thermodynamics and prec... more Computational materials design for lightweight steels with ICME approach: thermodynamics and precipitation strengthening simulation
Journal of Alloys and Compounds, 2018
IEEE Transactions on Magnetics, 2014
Optically highly transparent, soft magnetic thin films (4-18 nm thick) of Fe-B-Nb and Fe-B-Nb-Y-b... more Optically highly transparent, soft magnetic thin films (4-18 nm thick) of Fe-B-Nb and Fe-B-Nb-Y-based glassy metal targets were grown on quartz substrates by pulsed laser deposition, and their optical and magneto-optical properties were investigated over the visible spectrum (400-700 nm). All the films found to be fully amorphous in structure were continuous with uniform thickness and surface morphology. Their optical transmittance in the range 50%-85% was found to be film thickness dependent over the entire visible regime. The Verdet constant (V) and Faraday rotation angle (θf ) for different films (~4-18 nm) investigated as a function of wavelength (λ) show considerably higher values for the films of Fe-B-Nb-Y alloy as compared with those for Fe-B-Nb films, e.g., the ~4 nm film of Fe-B-Nb-Y alloy exhibits V ~ 49°/Oe cm and θf ~ 26°/μm while it decreased to ~29.4°/Oe and ~11.8°/μm, respectively, for the Fe-B-Nb alloy at λ = 611 nm. A linear relationship is found for the wavelength dependence of V and θf for both alloy systems. To the best of our knowledge, these values are considerably higher than those reported for any other magneto-optic material. The films are found to be soft magnetic with a high saturation moment while their magnetic coercivity values increases with thinness of the films. The observed combination of optical and magneto-optical properties of this new class of amorphous metallic films makes them viable for multifunctional magneto-optical applications.