| 1. |
- Andersson, Magnus, et al.
(author)
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Effect of Prestraining and Training on the γ→ε Transformation in Fe-Mn-Si Alloys
- 1995
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In: Journal de Physique IV. - : EDP Sciences. - 1155-4339 .- 1764-7177. ; 5:C8, s. 457-462
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Journal article (peer-reviewed)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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| 2. |
- Andersson, Magnus, et al.
(author)
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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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In: Materials transactions, JIM. - : Japan Institute of Metals. - 0916-1821 .- 2432-471X. ; 37:7, s. 1363-1370
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Journal article (peer-reviewed)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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| 3. |
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| 4. |
- Andersson, Magnus, et al.
(author)
-
The Influence of External Stresses on the Transformation Behaviour in a Fe-Mn-Si Alloy
- 1997
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In: Journal de Physique IV. - : EDP Sciences. - 1155-4339 .- 1764-7177. ; 7:C5, s. 411-416
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Journal article (peer-reviewed)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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| 5. |
- Andersson, Magnus, et al.
(author)
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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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In: Acta Materialia. - 1359-6454 .- 1873-2453. ; 46:11, s. 3883-3891
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Journal article (peer-reviewed)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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| 6. |
- Borgenstam, Annika, et al.
(author)
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Critical temperature for growth of martensite
- 1995
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In: Acta Metallurgica Et Materialia. - Oxford : Pergamon. - 0956-7151. ; 43:3, s. 945-954
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Journal article (peer-reviewed)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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| 7. |
- Crusius, Sabine, et al.
(author)
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On the growth of ferrite allotriomorphs in fe-c alloys
- 1992
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In: Zeitschrift für Metallkunde. - 0044-3093. ; 83:10, s. 729-738
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Journal article (peer-reviewed)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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| 8. |
- Crusius, Sabine, et al.
(author)
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On the numerical treatment of moving boundary problems
- 1992
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In: Zeitschrift für Metallkunde. - 0044-3093. ; 83:9, s. 673-678
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Journal article (peer-reviewed)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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| 9. |
- Engström, Anders, et al.
(author)
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COMPUTER-SIMULATION OF DIFFUSION IN MULTIPHASE SYSTEMS
- 1994
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In: Metallurgical and Materials Transactions. A. - 1073-5623 .- 1543-1940. ; 25:6, s. 1127-1134
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Journal article (peer-reviewed)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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| 10. |
- Forsberg, Annika, et al.
(author)
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Thermodynamic evaluation of the Fe-Mn-Si system and the γ/ε martensitic transformation
- 1993
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In: Journal of phase equilibria (Print). - 1054-9714 .- 1544-1032. ; 14:3, s. 354-363
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Journal article (peer-reviewed)abstract
- The thermodynamic properties of the Fe-Mn-Si system are analyzed by means of thermodynamic models for the individual phases. Special attention is paid to the γ → ε martensitic transition. A complete set of parameters, from which arbitrary sections of the phase diagram as well as the Ms and As temperatures may be calculated, is given.
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