| 1. |
- Becker, Chandler A., et al.
(författare)
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Thermodynamic modelling of liquids : CALPHAD approaches and contributions from statistical physics
- 2014
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 251:1, s. 33-52
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Tidskriftsartikel (refereegranskat)abstract
- We describe current approaches to thermodynamic modelling of liquids for the CALPHAD method, the use of available experimental methods and results in this type of modelling, and considerations in the use of atomic-scale simulation methods to inform a CALPHAD approach. We begin with an overview of the formalism currently used in CALPHAD to describe the temperature dependence of the liquid Gibbs free energy and outline opportunities for improvement by reviewing the current physical understanding of the liquid. Brief descriptions of experimental methods for extracting high-temperature data on liquids and the preparation of undercooled liquid samples are presented. Properties of a well-determined substance, B-2 O-3, including the glass transition, are then discussed in detail to emphasize specific modelling requirements for the liquid. We then examine the two-state model proposed for CALPHAD in detail and compare results with experiment and theory, where available. We further examine the contributions of atomic-scale methods to the understanding of liquids and their potential for supplementing available data. We discuss molecular dynamics (MD) and Monte Carlo methods that employ atomic interactions from classical interatomic potentials, as well as contributions from ab initio MD. We conclude with a summary of our findings.
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| 2. |
- Stormvinter, Albin
(författare)
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Low Temperature Austenite Decomposition in Carbon Steels
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Martensitic steels have become very important engineering materials in modern society. Crucial parts of everyday products are made of martensitic steels, from surgical needles and razor blades to car components and large-scale excavators. Martensite, which results from a rapid diffusionless phase transformation, has a complex nature that is challenging to characterize and to classify. Moreover the possibilities for modeling of this phase transformation have been limited, since its thermodynamics and kinetics are only reasonably well understood. However, the recent development of characterization capabilities and computational techniques, such as CALPHAD, and its applicability to ferrous martensite has not been fully explored yet.In the present work, a thermodynamic method for predicting the martensite start temperature (Ms) of commercial steels is developed. It is based mainly on information on Ms from binary Fe-X systems obtained from experiments using very rapid cooling, and Ms values for lath and plate martensite are treated separately. Comparison with the experimental Ms of several sets of commercial steels indicates that the predictive ability is comparable to models based on experimental information of Ms from commercial steels.A major part of the present work is dedicated to the effect of carbon content on the morphological transition from lath- to plate martensite in steels. A range of metallographic techniques were employed: (1) Optical microscopy to study the apparent morphology; (2) Transmission electron microscopy to study high-carbon plate martensite; (3) Electron backscattered diffraction to study the variant pairing tendency of martensite. The results indicate that a good understanding of the martensitic microstructure can be achieved by combining qualitative metallography with quantitative analysis, such as variant pairing analysis. This type of characterization methodology could easily be extended to any alloying system and may thus facilitate martensite characterization in general.Finally, a minor part addresses inverse bainite, which may form in high-carbon alloys. Its coupling to regular bainite is discussed on the basis of symmetry in the Fe-C phase diagram.
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| 3. |
- Strandlund, Henrik
(författare)
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Simulation of diffusional processes in alloys : techniques and applications
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns computer simulation of diffusional processes in alloys. The main focus is on the development of simulation techniques for diffusion in single-phase domains, but also diffusion controlled phase-transformations and interfacial processes are discussed. Different one-dimensional simulation techniques for studying the Kirkendall effect are developed and analyzed. Comparisons with experimentally observed marker migration show good agreement for small shifts and comparisons with observed Kirkendall porosity show reasonable agreement under the assumption that a certain supersaturation is needed before the vacancies coalesce into pores. A convenient approach in simulations of kinetics is to use thermodynamic software, e.g. Thermo-Calc, to calculate thermodynamic quantities, e.g. chemical potentials, required in the simulation. The main drawback with such an approach is that it will generate a large amount of additional computational work. To overcome this problem a method that decreases the amount of computational work has been developed. The new method is based on artificial neural networks (ANN). By training the ANN to estimate thermodynamic quantities a significant increase in computational speed was obtained. By calculating the dissipation of available driving force due to diffusion inside migrating interfaces an approach for including the effect of solute drag in computer simulations of grain growth and phase transformations has been developed. The new method is based on an effective interfacial mobility and simulations of grain growth have been performed in binary and ternary systems using experimentally assessed model parameters.
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| 4. |
- Alvares, E. D., et al.
(författare)
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An assessment of Fe-Nb-B melts using the two-state liquid model
- 2020
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Ingår i: Calphad. - : Elsevier Ltd. - 0364-5916 .- 1873-2984. ; 68
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous alloys of the (Fe-Co-Ni)-(Cr-Mo-Nb)-B system are promising materials to supply the demands for higher wear resistance components in the petrochemical industry. Since the development of the CALPHAD method, the development of new metallic alloys has been accompanied by thermodynamic modelling and calculations. The prediction of the formation of amorphous alloys requires special care with the modeling of the liquid and or an amorphous phase. As a initial stage in the more complex system, the basic Fe-Nb-B ternary system was selected. In order to predict the stability and tendencies of transformations of these amorphous alloys, the Fe-Nb-B system was reassessed using Ågren's two-state model to describe the liquid phase. The results of the present assessment show very good agreement with the recently reported stable phase diagram. Furthermore, the use of the two-state model for the liquid is more accurate and physically consistent when evaluating transformations from supercooled liquid, as shown it the present work.
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| 5. |
- Andersson, Egil, 1981-, et al.
(författare)
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Core-valence double photoionization of the CS2 molecule
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:9, s. 94305-
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Tidskriftsartikel (refereegranskat)abstract
- Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy. (C-) 2010 American Institute of Physics. [doi: 10.1063/1.3469812]
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| 6. |
- Andersson, Magnus, et al.
(författare)
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Effect of Prestraining and Training on the γ→ε Transformation in Fe-Mn-Si Alloys
- 1995
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Ingår i: Journal de Physique IV. - : EDP Sciences. - 1155-4339 .- 1764-7177. ; 5:C8, s. 457-462
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Tidskriftsartikel (refereegranskat)abstract
- The effect of training and predeformation on the martensitic transformation is investigated. It is concluded that MS as a function of predeformation strain must have a maximum at around 3% strain. Prestrains less than 5% will enhance the martensitic transformation whereas larger prestrains depress it due to strain hardening of the γ phase.
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| 7. |
- Andersson, Magnus, et al.
(författare)
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Effects of recrystallization and grain size on the martensitic transformation in Fe-31% Mn-5% Si alloy
- 1996
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Ingår i: Materials transactions, JIM. - : Japan Institute of Metals. - 0916-1821 .- 2432-471X. ; 37:7, s. 1363-1370
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Tidskriftsartikel (refereegranskat)abstract
- The effects of recrystallization and grain size have been studied in an Fe-31%Mn-5%Si shape memory alloy. The amount of martensite formed in samples which have been hot rolled at 1373 K and subsequently homogenized for 24 h at 1273 K followed by a final 30 min anneal at 1323 K is twice as large as in samples which have been hot rolled and homogenized in the same way as the former followed by a compression and a subsequent recrystallization at 1323 K for 30 min. The only difference between the samples is the plastic deformation induced by the compression. We thus conclude that some effect of the compressive deformation remains despite the recrystallization and suppresses the subsequent martensite formation. However, we have not yet been able to identify this effect. This matter will be subject to further investigations. No significant change is found in the M(S) and A(S) temperatures for the gamma <----> epsilon transformations determined by DSC. When the grain size varies between 40 and 160 mu m in completely recrystallized samples the variation in transformation temperatures is small, less than 10 K.
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| 8. |
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| 9. |
- Andersson, Magnus, et al.
(författare)
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The Influence of External Stresses on the Transformation Behaviour in a Fe-Mn-Si Alloy
- 1997
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Ingår i: Journal de Physique IV. - : EDP Sciences. - 1155-4339 .- 1764-7177. ; 7:C5, s. 411-416
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Tidskriftsartikel (refereegranskat)abstract
- The influence of external stresses on the transformation behaviour has been studied for a polycrystalline Fe-3 IMn-SSi alloy exhibiting the y-+& martensitic transformation. Samples have been loaded at temperatures above the M, temperature, cooled with a constant external load to a temperature below the M, temperature and subsequently heated without load to a temperature above the A, temperature of the alloy. Stress, strain and temperature have been continuously measured and transformation temperatures and strains have been determined from the change in strain during the transformation. It has been found that the M, temperature during cooling with load is not influenced by 0.3-2 % plastic pre-deformation of the austenite whereas there is a substantial increase in the transformation strain, i.e. variants with a favourable orientation are enhanced by pre-strain of austenite.
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| 10. |
- Andersson, Magnus, et al.
(författare)
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Unified thermodynamic analysis of the stress-assisted γ→ε martensitic transformation in Fe–Mn–Si alloys
- 1998
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Ingår i: Acta Materialia. - 1359-6454 .- 1873-2453. ; 46:11, s. 3883-3891
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Tidskriftsartikel (refereegranskat)abstract
- A unified thermodynamic analysis has been developed which allows the combined complex effects of applied stresses and alloy composition on the martensite start temperature, Ms(σ), to be explained and predicted. In this unified analysis, a thermodynamic analysis of the effect of applied stress on the relative stability of the high and low temperature phase is combined with existing thermodynamic descriptions of the alloy system. The calculated results are compared with experimental results for the γ→ martensitic transformation in Fe–Mn–Si shape memory alloys. For single crystals, the comparison shows that the influence of applied stresses can be directly predicted with a reasonable accuracy for a wide composition range. By integrating a polycrystallinity parameter in the analysis it is shown that the calculations are also valid for polycrystalline alloys. Application of this analysis to experimental values of Ms(σ) can also generate useful data for future optimizations of the thermodynamic description of several alloy systems.
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| 11. |
- Asp Grönhagen, Klara, 1973-
(författare)
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Phase-field modeling of surface-energy driven processes
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surface energy plays a major role in many phenomena that are important in technological and industrial processes, for example in wetting, grain growth and sintering. In this thesis, such surface-energy driven processes are studied by means of the phase-field method. The phase-field method is often used to model mesoscale microstructural evolution in materials. It is a diffuse interface method, i.e., it considers the surface or phase boundary between two bulk phases to have a non-zero width with a gradual variation in physical properties such as energy density, composition and crystalline structure. Neck formation and coarsening are two important diffusion-controlled features in solid-state sintering and are studied using our multiphase phase-field method. Inclusion of Navier-Stokes equation with surface-tension forces and convective phase-field equations into the model, enables simulation of reactive wetting and liquid-phase sintering. Analysis of a spreading liquid on a surface is investigated and is shown to follow the dynamics of a known hydrodynamic theory. Analysis of important capillary phenomena with wetting and motion of two particles connected by a liquid bridge are studied in view of important parameters such as contact angles and volume ratios between the liquid and solid particles. The interaction between solute atoms and migrating grain boundaries affects the rate of recrystallization and grain growth. The phenomena is studied using a phase-field method with a concentration dependent double-well potential over the phase boundary. We will show that with a simple phase-field model it is possible to model the dynamics of grain-boundary segregation to a stationary boundary as well as solute drag on a moving boundary. Another important issue in phase-field modeling has been to develop an effective coupling of the phase-field and CALPHAD methods. Such coulping makes use of CALPHAD's thermodynamic information with Gibbs energy function in the phase-field method. With the appropriate thermodynamic and kinetic information from CALPHAD databases, the phase-field method can predict mictrostructural evolution in multicomponent multiphase alloys. A phase-field model coupled with a TQ-interface available from Thermo-Calc is developed to study spinodal decomposition in FeCr, FeCrNi and TiC-ZrC alloys.
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| 12. |
- Asp Grönhagen, Klara, et al.
(författare)
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Phase-field modelling of spinodal decomposition in TiAlN including the effect of metal vacancies
- 2015
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 95, s. 42-45
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Tidskriftsartikel (refereegranskat)abstract
- Using a CALPHAD approach together with a Cahn-Hilliard model, we describe the microstructure evolution in cubic Ti1-xAlxN including vacancies on the metal sublattice. Our results show that vacancy content has a pronounced effect on the decomposition kinetics. Furthermore, vacancies show a strong tendency to segregate to the coherent AlN-TiN interface regions. We illustrate how vacancies anneal to grain boundaries, and finally, we compare our prediction to experimental differential scanning calorimetry data and attribute the second peak in the thermogram to vacancy depletion.
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| 13. |
- Asp Grönhagen, Klara, et al.
(författare)
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Phase-field simulation of sintering and related phenomena : A vacancy diffusion approach
- 2006
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 54, s. 1241-1248
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Tidskriftsartikel (refereegranskat)abstract
- A phase-field model of sintering and related phenomena in a two-phase system and in a multi-phase system is presented. We consider diffusion of vacancies as the atomic mechanism for redistribution of material and we will use the familiar model of thermal vacancies in a crystal as our energy formulation. The solid material will thus be characterized by a low vacancy content and the surroundings by a very high vacancy content and a very low content of atoms. The surface of the solid body will be characterized by a continuous variation in vacancy content. The temporal development of particles during solid state sintering with effects such as wetting is shown in various simulations.
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| 14. |
- Asp, Klara, et al.
(författare)
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Phase-field simulaton of sintering based on vacancy diffusion effect of anisotropy
- 2005
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Ingår i: Solid-Solid Phase Transformations in Inorganic Material 2005, Vol 2. ; , s. 741-746
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Konferensbidrag (refereegranskat)abstract
- Recently the present authors presented a Phase-field model of sintering in a multiphase system. In the present contribution the major features of the model are summarized. The model is based on diffusion of vacancies as the atomic mechanism for redistribution of material. The solid material is characterized by a low vacancy content and the surroundings by a very high vacancy content and a very low content of atoms. The surface of the solid body is characterized by a continuous variation in vacancy content. The temporal development of particles during solid state sintering with effects such as wetting has been shown previously and here we discuss the effect of a highly anisotropic interfacial energy on the morphological evolution of the particles.
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| 15. |
- Barkar, Thomas, et al.
(författare)
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Creep simulation of 9-12% Cr steels using the composite model with thermodynamically calculated input
- 2005
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 395:1-2, s. 110-115
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Tidskriftsartikel (refereegranskat)abstract
- Creep of 9-12% Cr steels is modeled using the composite model, developed by Blum et al. [R. Sedlacek, W. Blum, Comput. Mater. Sci. 25 (2002) 200], and thermodynamic calculations based on the Calphad approach. The composite model yields a physical description of the deformation behavior of materials that have a pronounced heterogeneous dislocation structure and is briefly surveyed. A few of the input parameters have been thermodynamically calculated using Thermo-Calc and introduced to the main program via a programming interface. This combined approach allows us to simulate the creep deformation behavior with less extensive microstructural investigations. This is a step towards enabling predictions of the creep behavior predominantly based on the nominal composition, heat treatment and mechanical load. Simulation results for two different 9-12% Cr steels are presented.
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| 16. |
- Barkar, Thomas, et al.
(författare)
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Effect of concentration dependent gradient energy coefficient on spinodal decomposition in the Fe-Cr system
- 2018
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Ingår i: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 143, s. 446-453
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 17. |
- Barkar, Thomas
(författare)
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Modelling phase separation in Fe-Cr alloys : A continuum approach
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The formation of Cr-rich and Fe-rich domains upon ageing of an initially homogeneous Fe-Cr alloy at elevated temperatures (300-600 ºC) is commonly referred to as phase separation. The behaviour originates from a miscibility gap in the Fe-Cr phase diagram. The boundary of the miscibility gap is denoted the binodal, and the line where the second derivative of the molar Gibbs energy w.r.t. composition is zero, the spinodal. In the region between the binodal and spinodal lines, the phase separation is said to occur by means of nucleation and growth. Inside the spinodal line, no thermally activated nucleation event is needed, and the initially homogeneous alloy decomposes "spinodally" into Cr-rich and Fe-rich regions. This type of phase transformation can be viewed as a continuous build up of Cr-rich regions, that also are interconnected, forming a microstructure characteristic for alloys decomposed spinodally. Phase separation has been of great interest within the metallurgical community as well as industry, due to its embritteling effect. Phase separation in Cr-rich ferritic steels, and thus embrittlement, sets a practical upper service temperature of ~300 ºC for Cr-containing ferrites. It is desirable to develop understanding and modelling capability for decomposing alloy systems, since such knowledge could be used to relieve the limitation in service temperature. The current work has been focused around the development and use of computer simulations, using thermodynamic and kinetic input from databases, in order to progress towards alloy design where decomposition is minimized. Simulations in this work are based on solving the so called Cahn-Hilliard equation, where an important parameter is the gradient energy, since it influences both the morphology and rate of decomposition in the simulations. An attempt at formulating a general model for the gradient energy coefficients in multi-component systems has been made, but has yet to be properly tried against experimental data. Improvements, and insights, to the initial state used in simulations has also been achieved. The combination of above mentioned efforts is a step towards a predictive tool for decomposition of complex alloys. Such a tool could not only be an aid in future alloy design, but also be used as an aid as a diagnosis tool in life time assessment of critical components already in use and thereby difficult to assess on site by means of in-destructive testing, typically components in nuclear power facilities.
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| 18. |
- Barkar, Thomas, et al.
(författare)
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Phase field modeling of spinodal decomposition in Fe-Cr based alloys
- 2015
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Ingår i: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015. - : International Conference on Solid-Solid Phase Transformations in Inorganic Materials. - 9780692437360 ; , s. 827-828
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Konferensbidrag (refereegranskat)
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| 19. |
- Bergman, Ola
(författare)
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Studies of oxide reduction and nitrogen uptake in sintering of chromium-alloyed steel powder
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The powder metallurgy (PM) process route is very competitive for mass production of structural steel components with complex shape, due to efficient material utilisation, low energy consumption, and short overall production time. The most commonly used alloying elements are the processing friendly metals Cu, Ni and Mo. However, the prices for these metals are today high and volatile, which threatens to make the PM process less competitive compared to conventional metal forming processes. Consequently, there is a strong desire in the PM industry to increase the use of less costly alloying elements. Cr is an attractive alternative since it, besides low cost, provides high hardenability and also recyclable components. The drawback is that Cr has high affinity for oxygen, which makes oxidation and oxide reduction in PM processing of Cr-alloyed materials a challenging issue. Furthermore, the interaction between nitrogen and Cr-alloyed powder during processing is important to consider, since Cr also has high nitrogen affinity and is prone to form nitrides. The aim of the research work presented in this thesis was to study oxide reduction and nitrogen uptake in sintering of Cr-alloyed steel powder. Water-atomized powder grades pre-alloyed with 1.5-3% Cr were used as test materials. Sintering experiments were performed in N2/H2 (90/10) atmospheres with test bars pressed to density 7.0-7.2 g/cm3. The oxygen content of the sintering atmosphere was varied and different sintering temperatures and cooling rates were applied. The experimental study has been complemented with thermodynamic calculations using the software Thermo-Calc. The oxygen partial pressure should be below 4 x 10-18 atm in order to have reducing conditions during sintering at 1120°C of steel powder pre-alloyed with 3% Cr. With graphite added to the powder, conditions are reducing at higher oxygen partial pressures (up to 10-16 atm) due to favourable conditions locally in the material. Sintering at 1120°C for 30 minutes leads to incomplete reduction of Cr-oxides in the Cr-alloyed PM grades, but remaining oxides are not detrimental for mechanical properties of the PM components. Increased sintering temperature is beneficial for the oxide reduction kinetics and practically all oxides are reduced after sintering for 30 minutes above 1200°C. Nitrogen uptake by Cr-alloyed steel powder from N2-based sintering atmospheres is strongly dependent on the cooling rate applied after sintering. No nitrides appear in the sintered material and mechanical properties are not affected when normal cooling rates (0.5-1°C/s) are applied. Very low cooling rates (such as 0.05°C/s) may lead to grain boundary precipitation of Cr-nitrides in the sintered material.
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| 20. |
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| 21. |
- Bonvalet, M., et al.
(författare)
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Modelling of prismatic grain growth in cemented carbides
- 2019
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Ingår i: International journal of refractory metals & hard materials. - : ELSEVIER SCI LTD. - 0263-4368. ; 78, s. 310-319
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 22. |
- Bonvalet-Rolland, Manon, et al.
(författare)
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Kinetic theory of nucleation in multicomponent systems : An application of the thermodynamic extremum principle
- 2019
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Ingår i: Acta Materialia. - : Acta Materialia Inc. - 1359-6454 .- 1873-2453. ; 171, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 23. |
- Borgenstam, Annika, et al.
(författare)
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Critical temperature for growth of martensite
- 1995
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Ingår i: Acta Metallurgica Et Materialia. - Oxford : Pergamon. - 0956-7151. ; 43:3, s. 945-954
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Tidskriftsartikel (refereegranskat)abstract
- Ms may be defined as the temperature below which the formation of martensite starts upon cooling. It may also be useful to define Mg, the temperature below which martensite can grow if it is already nucleated. In order to analyze the mechanism of martensite formation, it is essential to know the difference Mg - Ms. We have tried to evaluate Mg - Ms for an Fe-C alloy with a decarburized surface zone in order to induce nucleation. The samples were studied by means of electron microprobe, serial sectioning and optical microscopy. The results indicate that Mg is surprisingly close to Ms. The possibility that Mg is controlled by growth rather than nucleation is discussed.
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| 24. |
- Borgenstam, Annika, et al.
(författare)
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DICTRA, a tool for simulation of diffusional transformations in alloys
- 2000
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Ingår i: Journal of phase equilibria (Print). - : Springer Science and Business Media LLC. - 1054-9714 .- 1544-1032 .- 1863-7345. ; 21:3, s. 269-280
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Tidskriftsartikel (refereegranskat)abstract
- In the present paper, a general survey of the diffusion-controlled transformations (DICTRA) software is given. DICTRA is an engineering tool for diffusion simulations in multicomponent alloys. The simulations are based on multicomponent diffusion and thermodynamic data, both obtained by analyzing and assessing experimental information. This allows for many different cases to be studied as soon as the underlying data are available. DICTRA is not a complete simulation tool because only geometries that can be transformed into one space variable can be treated, but many well posed problems of practical interest may be solved. The program contains several different models, which are discussed in the present paper. Each model has its own applications and several examples from recent simulations are given in order to demonstrate the usage of the particular models.
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| 25. |
- Borgenstam, Annika, et al.
(författare)
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Metallographic evidence of carbon diffusion in the growth of bainite
- 2009
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 57:11, s. 3242-3252
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Tidskriftsartikel (refereegranskat)abstract
- There are two paradigms regarding the formation of bainite. One is based on the first stage being rapid, diffusionless growth or acicular ferrite and the subsequent formation of carbide occurring by precipitation from the supersaturated ferrite. All assumption that the first stage occurs as a series of subsequent rapid steps resulting in sub-units plays an important role as an explanation of the not so rapid growth observed macroscopically. The other paradigm is based on the first stage being the formation of acicular ferrite under carbon diffusion and on the subsequent growth of carbide and ferrite side by side. Metallographic observations are presented that support the second paradigm. It is difficult to see how they can be accounted for by the first paradigm, in particular the observation of the shapes of sub-units.
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| 26. |
- Borgenstam, Annika, et al.
(författare)
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On the Symmetry Among the Diffusional Transformation Products of Austenite
- 2011
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 42A:6, s. 1558-1574
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Tidskriftsartikel (refereegranskat)abstract
- Information on the diffusional transformation products of austenite in high-carbon steels is reviewed and supplemented with new microscopic studies. A comparison with transformation products in low-carbon steels indicates that there is a symmetry with pearlite in the middle, where ferrite and cementite are equal partners, and with acicular ferrite or cementite on each side. They both form with a surface relief, and at lower temperatures, each one is the leading phase in a eutectoid microstructure, bainite and inverse bainite, respectively. However, there is an asymmetry because at low temperatures bainite appears in high-carbon steels but inverse bainite never appears in low-carbon steels. At a constant high carbon content, there is another kind of symmetry, which is related to temperature. At intermediate temperatures the eutectoid reaction results in spherical nodules in which the cementite constituent originates from Widmanstatten plates. It turns spiky at both higher and lower temperatures with the leading phase in the spikes being cementite at higher temperatures and ferrite at lower temperatures. In the first kind of symmetry, there is an abrupt change among the three reaction products; in the second kind of symmetry, there is a gradual change. Accepting that all the eutectoid microstructures form by diffusion of carbon, one may explain the existence of both symmetries by the variation of the ratio of the supersaturations of ferrite and cementite with carbon content and with temperature.
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| 27. |
- Borgh, Ida, et al.
(författare)
-
Effect of carbon activity and powder particle size on WC grain coarsening during sintering of cemented carbides
- 2014
-
Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 42, s. 30-35
-
Tidskriftsartikel (refereegranskat)abstract
- Liquid-phase sintering is an important step in the production of cemented carbides. During sintering, the average WC grain size increases, leading to a coarser structure, which affects the performance of the final product. The coarsening occurs by dissolution of small grains and growth of large grains. In the present work, the effect of high carbon activity during sintering on the WC grain coarsening has been evaluated using electron backscattered diffraction (EBSD) and the results have been compared with a previous work where sintering was performed at a lower carbon activity. A more homogeneous grain size distribution was observed in alloys sintered at a high carbon activity. In addition, the effect of the initial powder particle size distribution was investigated. It was found that the coarsening rate of a WC powder with an initial small average grain size is significantly higher as compared to the coarsening rate for a powder with a larger initial average grain size. The results obtained emphasize the importance of considering the complete particle size distribution in order to predict coarsening.
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| 28. |
- Borgh, Ida, et al.
(författare)
-
Influence of nitrogen Gas pressure on the miscibility Gap in the Ti-Zr carbonitride system
- 2012
-
Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 32, s. 11-15
-
Tidskriftsartikel (refereegranskat)abstract
- The microstructure of cemented carbides with a gradient structure at the surface consists of WC, cubic carbonitrides and a binder phase. The carbonitrides can, for example, consist of Ti(C,N)-Zr(C,N) where it is reasonable to believe that there is a miscibility gap with Ti-rich and Zr-rich carbonitrides. In the present work, the effect of the N-2-gas pressure on the equilibrium composition of the miscibility gap in the (Ti,Zr)(C,N) system has been investigated. In the study, the carbonitride system is in equilibrium with: WC, liquid binder, graphite and, N-2-gas of different pressures. Both Fe and Co are used as binder phase to study the effect of the binder phase. The results verify that there is a miscibility gap in the carbonitride system and that the region of the miscibility gap will change when N is introduced. There is a critical N-2-gas pressure lower than 0.1 bar and above that pressure the compositions of the carbonitride are rather constant as a result of the formation of a surface rim.
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| 29. |
- Borgh, Ida, et al.
(författare)
-
Microstructure, grain size distribution and grain shape in WC-Co alloys sintered at different carbon activities
- 2014
-
Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368 .- 0958-0611. ; 43, s. 205-211
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of cemented carbides strongly depend on the WC grain size and it is thus crucial to control coarsening of WC during processing. The aim of this work was to study the effect of sintering at different carbon activities on the final microstructure, as well as the coarsening behavior of the WC grains, including the size distribution and the shape of WC grains. These aspects were investigated for five WC-Co alloys sintered at 1410 degrees C for 1 h at different carbon activities in the liquid, in the range from the graphite equilibrium (carbon activity of 1) to the eta (M6C) phase equilibrium (carbon activity of 0.33). The grain size distribution was experimentally evaluated for the different alloys using EBSD (electron backscatter diffraction). In addition, the shape of the WC grains was evaluated for the different alloys. It was found that the average WC grain size increased and the grain size distribution became slightly wider with increasing carbon activity. Comparing the two three-phase (WC-Co-eta and WC-Co-graphite) alloys a shape change of the WC grains was observed with larger grains having more planar surfaces and more triangular shape for the WC-Co-graphite alloy. It was indicated that in alloys with a relatively low volume fraction of the binder phase the WC grain shape is significantly affected by impingements. Moreover, after 1 h of sintering the WC grains are at a non-equilibrium state with regards to grain morphology. (C) 2013 Elsevier Ltd. All rights reserved.
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| 30. |
- Borgh, Ida, et al.
(författare)
-
On the three-dimensional structure of WC grains in cemented carbides
- 2013
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 61:13, s. 4726-4733
-
Tidskriftsartikel (refereegranskat)abstract
- In the present work, the size distribution and shape of WC grains in cemented carbides (WC-Co), with different Co contents, have been investigated in three dimensions. Direct three-dimensional (3-D) measurements, using focused ion beam serial sectioning and electron backscattered diffraction (EBSD), were performed and a 3-D microstructure was reconstructed. These measurements were supplemented by two-dimensional (2-D) EBSD and scanning electron microscopy on extracted WC grains. The data from 2-D EBSD collected on planar sections were transformed to three dimensions using a recently developed statistical method based on an iterative inverse Saltykov procedure. This stereological analysis revealed that the assumed spherical shape of WC grains during the Saltykov method is reasonable and the estimated 3-D size distribution is qualitatively in good agreement with the actual distribution measured from 3-D EBSD. Although the spherical assumption is generally fair, the WC grains have both faceted and rounded surfaces. This is a consequence of the relatively low amount of liquid phase during sintering, which makes impingements significant. Furthermore, the observed terraced surface structure of some WC grains suggests that 2-D nucleation is the chief coarsening mechanism to consider.
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| 31. |
- Borgh, Ida, et al.
(författare)
-
Synthesis and phase separation of (Ti,Zr)C
- 2014
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 66, s. 209-218
-
Tidskriftsartikel (refereegranskat)abstract
- Synthesis and phase separation of (Ti,Zr)C were investigated in the present work. The (Ti,Zr)C phase was synthesized at 2200 C and subsequently aged at 1300 C for different times. The microstructure was investigated using X-ray diffraction and electron microscopy, and supplemented by first-principles calculations. The (Ti,Zr)C phase separates into a lamellar nanostructure with alternating Ti- and Zr-rich face-centered cubic domains as well as non-stoichiometric TiC and ZrC. The lamellar structure is a consequence of phase separation within the miscibility gap that is directionally constrained by high coherency stresses, as indicated by the first-principles calculations. Moreover, the increased hardness due to the phase separation suggests that the mixed carbide could be used as a strengthening constituent in, for example, cemented carbides.
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| 32. |
- Bratberg, Johan, et al.
(författare)
-
Diffusion simulations of MC and M7C3 carbide coarsening in bcc and fcc matrix utilising new thermodynamic and kinetic description
- 2008
-
Ingår i: Materials Science and Technology. - : Informa UK Limited. - 0267-0836 .- 1743-2847. ; 24:6, s. 695-704
-
Tidskriftsartikel (refereegranskat)abstract
- A new thermodynamic database has been combined with an existing kinetic database to perform coarsening simulations in ternary systems including MC and M7C3 carbides in an fcc matrix. The kinetic database was revised taking into consideration the new experimental information on the Fe-Cr-V-C system obtained in the present work, and available experiments on the ternary Fe-Cr-C and Fe-V-C systems. After revision the agreement between experimental results and simulations was satisfactory. It was found that the interfacial energy of M7C3 was twice as large as that of the MC carbide. The calculations for commercial steels with 6 alloy elements gave results in satisfactory agreement with new experimental measurements. The present coarsening simulations use the calculated equilibrium state and the observed particle sizes as the state for the start of the simulations. All the simulations were performed with the DICTRA software.
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| 33. |
- Bratberg, Johan, 1975-
(författare)
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Phase equilibria and thermodynamic properties of high-alloy tool steels : theoretical and experimental approach
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The recent development of tool steels and high-speed steels has led to a significant increase in alloy additions, such as Co, Cr, Mo, N, V, and W. Knowledge about the phase relations in these multicomponent alloys, that is, the relative stability between different carbides or the solubility of different elements in the carbides and in the matrix phase, is essential for understanding the behaviour of these alloys in heat treatments. This information is also the basis for improving the properties or designing new alloys by controlling the amount of alloying elements. Thermodynamic calculations together with a thermodynamic database is a very powerful and important tool for alloy development of new tool steels and high-speed steels. By thermodynamic calculations one can easily predict how different amounts of alloying elements influence on the stability of different phases. Phase fractions of the individual phases and the solubility of different elements in the phases can be predicted quickly. Thermodynamic calculations can also be used to find optimised processing temperatures, e.g. for different heat treatments. Combining thermodynamic calculations with kinetic modelling one can also predict the microstructure evolution in different processes such as solidification, dissolution heat treatments, carbide coarsening, and the important tempering step producing secondary carbides. The quality of predictions based on thermodynamic calculations directly depends on the accuracy of the thermodynamic database used. In the present work new experimental phase equilibria information, both in model alloys containing few elements and in commercial alloys, has been determined and was used to evaluate and improve the thermodynamic description. This new experimental investigation was necessary because important information concerning the different carbide systems in tool steels and high-speed steels were lacking. A new thermodynamic database for tool steels and high-speed steels, TOOL05, has been developed within this thesis. With the new database it is possible to calculate thermodynamic properties and phase equilibria with high accuracy and good reliability. Compared with the previous thermodynamic description the improvements are significant. In addition the composition range of different alloying elements, where reliable results are obtained with the new thermodynamic database, have been widened significantly. As the available kinetic data did not always predict results in agreement with new experiments the database was modified in the present work. By coupling the new thermodynamic description with the new kinetic description accurate diffusion simulations can be performed for carbide coarsening, carbide dissolution and micro segregation during solidification.
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| 34. |
- Chen, Hao, et al.
(författare)
-
Application of interrupted cooling experiments to study the mechanism of bainitic ferrite formation in steels
- 2013
-
Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 61:12, s. 4512-4523
-
Tidskriftsartikel (refereegranskat)abstract
- New interrupted cooling experiments have been designed to study the kinetics of bainitic ferrite formation starting from a mixture of austenite and bainitic ferrite. It is found that the kinetics of bainitic ferrite formation during the cooling stage is determined by the isothermal holding time. The formation rate of bainitic ferrite at the beginning of the cooling decreases with increasing prior isothermal holding time. An unexpected stagnant stage during the cooling stage appears when the isothermal holding time increases to a critical point. There are two reasons for the occurrence of the stagnant stage: (i) a solute spike in front of the interface; and (ii) kinetic transition. A so-called Gibbs energy balance approach, in which the dissipation of Gibbs energy due to diffusion inside the interface and interface friction is assumed to be equal to the available chemical driving force, is applied to theoretically explain the stagnant stage. A kinetics transition from a fast growth mode without diffusion of Mn and Si inside the austenite-bainitic ferrite interfaces to a slow growth mode with diffusion inside the interface is predicted. The stagnant stage is caused by the transition to a slow growth mode. The Gibbs energy balance approach describes the experimental observations very well.
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| 35. |
- Chen, Q., et al.
(författare)
-
Analytical treatment of diffusion during precipitate growth in multicomponent systems
- 2008
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 56:8, s. 1890-1896
-
Tidskriftsartikel (refereegranskat)abstract
- We propose an approximate growth rate equation that takes into account both cross-diffusion and high supersaturations for modeling precipitation in multicomponent systems. We then apply it to an Fe-alloy in which interstitial C atoms diffuse much faster than substitutional solutes, and predict a spontaneous transition from slow growth under ortho-equilibrium to fast growth under the non-partitioning local equilibrium condition. The transition is caused by the decrease in the Gibbs-Thomson effect as the growing particle becomes larger. The results agree with DICTRA simulations where full diffusion fields are calculated.
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| 36. |
- Chen, Qing, et al.
(författare)
-
On Negative Diagonal Elements in the Diffusion Coefficient Matrix of Multicomponent Systems
- 2018
-
Ingår i: JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION. - : Springer. - 1547-7037 .- 1863-7345. ; 39:5, s. 592-596
-
Tidskriftsartikel (refereegranskat)abstract
- In multicomponent systems the diffusion coefficient turns into a matrix. The diagonal elements represent diffusion of a species caused by its own concentration gradient. In a thermodynamically stable binary alloy it is easy to see that this diagonal element must be positive but in a multicomponent system it is less obvious. The sign of the diagonal elements in the general case is discussed in this report. It is shown that the sign of an individual diagonal element has no physical meaning but can be changed by changing the dependent concentration variable. Only the sum of all the diagonal elements need to be positive in a stable system.
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| 37. |
- Costa e Silva, Andre, et al.
(författare)
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Applications of computational thermodynamics - the extension from phase equilibrium to phase transformations and other properties
- 2007
-
Ingår i: Calphad. - : Elsevier BV. - 0364-5916 .- 1873-2984. ; 31:1, s. 53-74
-
Tidskriftsartikel (refereegranskat)abstract
- Complex equilibria and phase transformations involving diffusion can now be calculated quickly and efficiently. Detailed examples are given for cases which involve varying degrees of non-equilibrium and therefore time-dependence. Despite very good agreement between such calculations and experimental results, many potential end-users are still not convinced that such techniques could be usefully applied to their own specific problems. Friendly graphic interface versions of calculating software are now generally available, so the authors conclude that the most likely source of the reluctance to use such tools lies in the formulation of relevant questions and the interpretation of the results. Although the potential impact of such tools was foreseen many years ago [M. Hillert, Calculation of phase equilibria, in: Conference on Phase Transformations, 1968], few changes in the relevant teaching curricula have taken into account the availability and power of such techniques. This paper has therefore been designed not only as a collection of interesting problems, but also highlights the critical steps needed to achieve a solution. Each example includes a presentation of the "real" problem, any simplifications that are needed for its solution, the adopted thermodynamic formulation, and a critical evaluation of the results. The availability of such examples should facilitate changes in subject matter that will both make it easier for the next generation of students to use these tools, and at the same time reduce the time and effort currently needed to solve such problems by less efficient methods. The first set of detailed examples includes the deoxidation of steel by aluminum; heat balance calculations associated with ladle additions to steel; the determination of conditions that avoid undesirable inclusions; the role of methane in sintering atmospheres; interface control during the physical vapour deposition of cemented carbide; oxidation of gamma-TiAl materials; and simulation of the thermolysis of metallorganic precursors for Si-C-N ceramics and interface reaction of yttrium silicates with SiC-coated C/C-SiC composites for heat shield applications. A second set of examples, more dependent on competitive nucleation and growth, includes segregation and carburization in multicomponent steels and features a series of sophisticated simulatons using DICTRA software. Interfacial and strain energies become increasingly important in defining phase nucleation and morphology in such problems, but relatively little information is available compared to free energy and diffusion databases. The final section therefore demonstrates how computational thermodynamics, semi-empirical atomistic approaches and first-principles calculations are being used to aid filling this gap in our knowledge. (c) 2006 Elsevier Ltd. All rights reserved.
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| 38. |
- Crusius, Sabine, et al.
(författare)
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On the growth of ferrite allotriomorphs in fe-c alloys
- 1992
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Ingår i: Zeitschrift für Metallkunde. - 0044-3093. ; 83:10, s. 729-738
-
Tidskriftsartikel (refereegranskat)abstract
- Different geometrical models of allotriomorphic growth of ferrite in undercooled austenite are investigated by means of numerical and analytical treatments of diffusional growth under local equilibrium. The results obtained by the numerical method are compared with analytical solutions for those cases where such solutions may be derived. An excellent agreement is obtained. The numerical method is subsequently applied to simulate the experiments by Aaronson et al. and some more recent experiments by Hougardy et al.. taking into account the concentration dependence of the diffusivity of C in austenite and the most recent thermodynamic assessment of the ferrite/austenite equilibrium. Taking into account the experimental uncertainties we conclude that the growth of allotriomorphic ferrite must be essentially controlled by long-range carbon diffusion in austenite.
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| 39. |
- Crusius, Sabine, et al.
(författare)
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On the numerical treatment of moving boundary problems
- 1992
-
Ingår i: Zeitschrift für Metallkunde. - 0044-3093. ; 83:9, s. 673-678
-
Tidskriftsartikel (refereegranskat)abstract
- Some numerical methods for solving a Stefan problem are discussed and compared with the exact solution. The growth of a planar particle from a supersaturated solution (or solidification from a supercooled liquid) is considered. It is found that the Murray-Landis method, based on a finite difference technique to solve the diffusion equation on a contracting grid, yields a poor accuracy for high supersaturations. The enthalpy method, also based on the finite difference technique and an interpolation formula for obtaining the interface position, shows a satisfactory performance at high supersaturations but a less satisfactory one at low supersaturations. It is demonstrated that the poor accuracy of the Murray-Landis method depends on the application of a less accurate flux-balance equation for finite time increments and the procedure for displacing the grid points. A modification of the Murray-Landis method is developed and is found to have superior numerical performance.
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| 40. |
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| 41. |
- Danila, Ion, et al.
(författare)
-
Hierarchical Chiral Expression from the Nano- to Mesoscale in Synthetic Supramolecular Helical Fibers of a Nonamphiphilic C(3)-Symmetrical pi-Functional Molecule
- 2011
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 133:21, s. 8344-8353
-
Tidskriftsartikel (refereegranskat)abstract
- The controlled preparation of chiral structures is a contemporary challenge for supramolecular science because of the interesting properties that can arise from the resulting materials, and here we show that a synthetic nonamphiphilic C(3) compound containing pi-functional tetrathiafulvalene units can form this kind of object. We describe the synthesis, characterization, and self-assembly properties in solution and in the solid state of the enantiopure materials. Circular dichroism (CD) measurements show optical activity resulting from the presence of twisted stacks of preferential helicity and also reveal the critical importance of fiber nucleation in their formation. Molecular mechanics (MM) and molecular dynamics (MD) simulations combined with CD theoretical calculations demonstrate that the (5) enantiomer provides the (M) helix, which is more stable than the (P) helix for this enantiomer. This relationship is for the first time established in this family of C(3) symmetric compounds. In addition, we show that introduction of the "wrong" enantiomer in a stack decreases the helical reversal barrier in a nonlinear manner, which very probably accounts for the absence of a "majority rules" effect. Mesoscopic chiral fibers, which show inverted helicity, i.e. (P) for the (S) enantiomer and (M) for the (R) one, have been obtained upon reprecipitation from dioxane and analyzed by optical and electronic microscopy. The fibers obtained with the racemic mixture present, as a remarkable feature, opposite homochiral domains within the same fiber, separated by points of helical reversal. Their formation can be explained through an "oscillating" crystallization mechanism. Although C(3) symmetric disk-shaped molecules containing a central benzene core substituted in the 1,3,5 positions with 3,3'-diamido-2,2'-bipyridine based wedges have shown peculiar self-assembly properties for amphiphilic derivatives, the present result shows the benefits of reducing the nonfunctional part of the molecule, in our case with short chiral isopentyl chains. The research reported herein represents an important step toward the preparation of functional mesostructures with controlled helical architectures.
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| 42. |
- Du, H., et al.
(författare)
-
Microstructural and compositional evolution of compound layers during gaseous nitrocarburizing
- 2000
-
Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 31:1, s. 195-211
-
Tidskriftsartikel (refereegranskat)abstract
- Compound layers developed at 848 K during gaseous nitrocarburizing of iron and iron-carbon specimens were investigated for several combinations of N and C activities imposed at the specimen surface by gas mixtures of NH3, N-2, CO2, and CO. The microstructural evolution of the compound layer was studied by light microscopy and by X-raydiffraction analysis. Composition-depth profiles were determined by electron probe (X-ray) microanalysis. Layer growth kinetics was investigated by layer thickness measurements. The influence Of the N and C activities on the microstructural and compositional evolution and the growth kinetics of the compound layers formed is discussed for the iron substrate. The results indicate that the microstructure is governed by a fast C and a slow N absorption at the surface in an early stage of gaseous nitrocarburizing. The influence of carbon in the substrate on the microstructural and compositional evolutions and on the growth kinetics was evaluated from comparing the results obtained for: a: normalized Fe-0.8C alloy with those for iron under identical nitrocarburizing conditions.
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| 43. |
- Edman Ansell, John, 1976-
(författare)
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Maktens tal och talets makt : Kunglig maktlegitimering i Erik XIV:s och Johan III:s tid
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examines how Erik XIV and Johan III of Sweden used ethos construction and rhetoric to legitimize the new strong royal power during their combined reign from 1561 to 1592. The study analyses three different crises of legitimacy to understand how the kings and their allies negotiated these challenges and how the various strategies used by the rulers affected their ability to expand the space of legitimate royal power. The three crises are the dynastic crisis, the crisis of church politics, and the foreign policy crisis. The source material used includes written speeches, official letters from the kings, instructions for negotiators, and sermons. A key argument of the study is that the art of rhetoric is central to understanding the political conflicts of this era, and that, furthermore, 16th-century Swedish political culture should be analyzed as a part of the European Renaissance. The historical period is framed as a transitional political phase between an older political culture where legitimacy often came from sources connected to personal relationships and a new political culture where stable institutions fill that function. The results show that the Swedish kings shaped their royal ethos very differently, mainly depending on Erik's position as a hereditary ruler with initially strong legitimacy and Johan's much more precarious position as the usurper of Erik's throne. Erik, therefore, based his ethos on sources of legitimacy more connected to institutional tropes and was subsequently criticized for his inability to form and retain virtuous relationships. As an effect, Johan's ethos had to be the opposite. Since both relational and institutional sources of legitimacy were available, it was valuable to control the rhetorical arena of political negotiation. Political adversaries often switched positions between them as it fitted their argument. Historians have often misconstrued this as signs of irrationality or even mental illness. Instead, the study argues that it should be interpreted as careful positioning by rulers sensitive to the effects and benefits of ethos construction. Therefore, the main conclusion of this thesis is that the politics of rulers steeped in the political culture of the renaissance must be analyzed through the filter of rhetoric.
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| 44. |
- Ekroth, M., et al.
(författare)
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Gradient zones in WC-Ti(C,N)-Co-based cemented carbides : Experimental study and computer simulations
- 2000
-
Ingår i: Acta Materialia. - 1359-6454 .- 1873-2453. ; 48:9, s. 2177-2185
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of surface zones with a composition gradient during sintering of WC-Ti(C,N)-Co cemented carbides has been studied experimentally and by computer simulations. The microstructure has been investigated with SEM and EPMA. The simulations are based on a solution of the multicomponent diffusion equations, coupled with thermodynamic calculations using thermodynamic descriptions of the individual phases. The results from the simulations are in good agreement with the experimental results, indicating that diffusion and the thermodynamic properties are the two major factors that control the gradient structure formation.
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| 45. |
- Engström, Anders, et al.
(författare)
-
COMPUTER-SIMULATION OF DIFFUSION IN MULTIPHASE SYSTEMS
- 1994
-
Ingår i: Metallurgical and Materials Transactions. A. - 1073-5623 .- 1543-1940. ; 25:6, s. 1127-1134
-
Tidskriftsartikel (refereegranskat)abstract
- A general model to treat multicomponent diffusion in multiphase dispersions is presented. The model is based on multicomponent diffusion data and basic thermodynamic data and contains no adjustable parameters. No restriction is placed on the number of components or phases that take part in the calculations, as long as the necessary thermodynamic and kinetic data are available. The new model is implemented into the DICTRA software, which makes use of THERMO-CALC to handle the thermodynamics. The model is applied to carburization of Ni alloys and heat treatment of welded joints between dissimilar materials. In both cases, the diffusion is accompanied by carbide formation or dissolution. A good agreement between experiments and calculations is found, despite the fact that no adjustable parameters are needed.
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| 46. |
- Erneman, J., et al.
(författare)
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Comparison between quantitative metallography and modeling of sigma-phase particle growth in AISI 347 stainless steel
- 2005
-
Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 36A:10, s. 2595-2600
-
Tidskriftsartikel (refereegranskat)abstract
- A comparison was made between two experimental methods to determine the (T-phase volume fraction and three methods to model a-phase growth in a niobium-stabilized stainless steel (AISI 347). The a-phase volume fraction and precipitate size were determined in material statically aged and creep deformed at 700 degrees C with both KOH etched specimens using bright field optical microscopy (OM/BF) (conventional method) and specimens etched with oxalic acid using scanning electron microscopy and backscattered electrons (SEM/BSE) (new method). Both experimental methods used manual thresholding together with digital image analysis. The calculations were made with DICTRA software, using both the TCFE database and the SSOL database with some modification concerning the effect of silicon on the stability of sigma-phase particles. The modeled sigma-phase volume- fractions showed rather good agreement with the measured results from statically aged material using the new method. It was found that the stabilizing effect of silicon on sigma phase should be included in the thermodynamic database used for modeling.
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| 47. |
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| 48. |
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| 49. |
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| 50. |
- Erneman, J., et al.
(författare)
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Precipitation reactions caused by nitrogen uptake during service at high temperatures of a niobium stabilised austenitic steel
- 2004
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 52:14, s. 4337-4350
-
Tidskriftsartikel (refereegranskat)abstract
- Precipitation phenomena in type 347 austenitic stainless steels have been investigated after long-term heat treatment and creep in air at 700 and 800 degreesC. Nitrogen uptake was observed during long-term creep testing at 800 degreesC. No such effect was observed at 700 degreesC although times up to about 70,000 h were used. The major phases precipitated after long time exposure at 800 degreesC were primary Nb(C,N), Z-phase, Cr2N and M23C6, while primary Nb(C,N), secondary Nb(C,N) and sigma-phase were the major phases at 700 degreesC. Z-phase precipitated in both intragranular and intergranular form at 800 degreesC. Large precipitates exhibiting a core/rim structure showed a rim of Z-phase surrounding undissolved primary Nb(C,N). The microstructural evolution during creep deformation in air at 800 degreesC was modelled thermodynamically. The model satisfactorily predicts nitrogen uptake and the essential features of the evolution of the microstructure with time. The precipitation sequence could be qualitatively described, although it was not possible to model the formation of all precipitates.
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