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The theory of transformations in metals and alloys

TL;DR: In this paper, the authors present a general introduction to the theory of transformation kinetics of real metals, including the formation and evolution of martensitic transformations, as well as a theory of dislocations.
Abstract: Part I General introduction. Formal geometry of crystal lattices. The theory of reaction rates. The thermodynamics of irreversable processes. The structure of real metals. Solids solutions. The theory of dislocations. Polycrystalline aggregates. Diffusion in the solid state. The classical theory of nucleation. Theory of thermally activated growth. Formal theory of transformation kinetics. Part II Growth from the vapour phase. Solidification and melting. Polymorphic Changes. Precipitation from supersaturated solid solution. Eutectoidal transformations. Order-disorder transformations. Recovery recrystalisation and grain growth. Deformation twinning. Characteristics of martensic transformations. Crystallography of martensitic transformations. Kinetics of martensitic transformations. Rapid solidification. Bainite steels. Shape memory alloys.
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TL;DR: In this article, the influence of the alloying elements on the rate of the intermetallic β-to-α transformation is studied, and the results of the Finite Element Model are validated with experimental data.
Abstract: An homogenisation process is applied to as cast billets Al–Mg–Si alloys in order to improve the extrudability. During this homogenisation, plate-like β-AlFeSi phase transforms to a more rounded α-Al(FeMn)Si phase which are more favourable for the extrusion process. In this paper, the influence of the alloying elements on the rate of the intermetallic β-to-α transformation is studied. A Finite Element Model (FEM) predicts the kinetics of the β-to-α transformation for various Mn and Si concentrations. The software package Thermo-Calc is used to derive the equilibrium solubilities for various alloy compositions. These solubilities are used in the Finite Element Method as boundary conditions for the interfacial concentrations of the intermetallics. Subsequently, the results of the Finite Element Model are validated with experimental data.

142 citations

Journal ArticleDOI
TL;DR: The shape memory and the superelasticity effect in a nonmartensitic Ti48.5Ni51.5 alloy, which has no martensitic transformation but undergoes a "strain glass" transition, is shown.
Abstract: The shape memory effect and superelasticity are usually found in alloys exhibiting spontaneous martensitic transformation. Thus it is hard to imagine that such interesting effects can appear in a system without a martensitic transformation. In this Letter we show shape memory and the superelasticity effect in a nonmartensitic ${\mathrm{Ti}}_{48.5}{\mathrm{Ni}}_{51.5}$ alloy, which has no martensitic transformation but undergoes a ``strain glass'' transition. In situ x-ray diffraction experiment showed that the shape memory and superelasticity in strain glass stem from a stress-induced strain glass to martensite transformation and its reverse transformation. The new shape memory and superelasticity in strain glass extends the regime of the shape memory effect and superelasticity and may lead to novel applications.

142 citations

Journal ArticleDOI
TL;DR: In this article, it is shown that for phase boundaries that propagate subsonically, this approach is equivalent to the imposition of a particular kinetic relation at the interface between the phases.
Abstract: This paper is concerned with the propagation of phase boundaries in elastic bars. It is known that the Riemann problem for an elastic bar capable of undergoing isothermal phase transitions need not have a unique solution, even in the presence of the requirement that the entropy of any particle cannot decrease upon crossing a phase boundary. For a special class of elastic materials, the authors have shown elsewhere that if all phase boundaries move subsonically with respect to both phases, this lack of uniqueness can be resolved by imposing a nucleation criterion and a kinetic relation for the relevant phase transition. Others have singled out acceptable solutions on the basis of a theory that adds effects due to viscosity and second strain gradient to the elastic part of the stress. It is shown that, for phase boundaries that propagate subsonically, this approach is equivalent to the imposition of a particular kinetic relation at the interface between the phases.

140 citations

Journal ArticleDOI
TL;DR: In this paper, a model is developed to predict the precipitation and coarsening kinetics of the Al3Sc phase in Al-Sc alloys, which is based on the N-model framework of Kampmann and Wagner.

140 citations

Journal ArticleDOI
TL;DR: In this article, the authors determined the kinetics of sigma phase formation in UNS S31803 Duplex Stainless Steel (DSS), describing the phase transformations that occur in isothermal aging between 700 and 900 oC for time periods up to 1032 hours.
Abstract: This work determines the kinetics of sigma phase formation in UNS S31803 Duplex Stainless Steel (DSS), describing the phase transformations that occur in isothermal aging between 700 and 900 oC for time periods up to 1032 hours, allowing the determination of the Time-Temperature-Precipitation (TTP) diagram for sigma phase and proposing a model to predict the kinetics of sigma phase formation using a Johnson-Mehl-Avrami (JMA) type expression. The higher kinetics of sigma phase formation occurs at 850 oC. However, isothermal aging between 700 and 900 oC for time periods up to 1032 hours are not sufficient to the establishment of thermodynamic equilibrium. Activation energy for both nucleation and growth of sigma phase is determined (185 kJ.mol-1) and its value is equivalent to the activation energy for Cr diffusion in ferrite, indicating that diffusion of Cr is probably the major thermally activated process involved in sigma phase formation. The determined JMA type expression presents good fit with experimental data between 700 and 850 oC.

139 citations