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The theory of transformations in metals and alloys
01 Jan 1965-
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, a simple method is proposed to verify the applicability of the Johnson-Mehl-Avrami (JMA) model as well as the basic assumptions in kinetic analysis.
Abstract: Thermal Analysis techniques are widely used to study the crystallization kinetics in amorphous solids. Such experimental data are frequently interpreted in terms of the Johnson-Mehl-Avrami (JMA) nucleation-growth model. This paper discusses the limits of such approach. A simple method is proposed to verify the applicability of the JMA model as well as the basic assumptions in kinetic analysis. It is shown that the autocatalytic model includes the JMA model and it is a plausible description of the crystallization kinetics. The main advantage of the autocatalytic model is the possibility to describe quantitatively the kinetics of complex crystallization processes. The experimental data for crystallization of a chalcogenide glass analyzed in this paper clearly demonstrate rather complex nature of these processes. As a consequence it is very difficult to explore real kinetic mechanism of the crystallization process unless some complementary studies are made.
47 citations
TL;DR: In this paper, the Johnson-Mehl-Avrami theory of transformation kinetics was applied to the isothermal crystallization of a nearly stoichiometric Na2O·2CaO·3SiO2 glass.
Abstract: Experiments were carried out to test the validity of the Johnson-Mehl-Avrami theory of transformation kinetics. The isothermal crystallization of a nearly stoichiometric Na2O·2CaO·3SiO2 glass was studied at 627°C and 629°C by optical microscopy, density measurements and X-ray diffraction. Both nucleation and growth rates were measured by single and double stage heat treatments up to very high volume fractions transformed and the experimental data for crystallinity were compared with the calculated values at the two temperatures. The early crystallization stages were well described by theory for the limiting case of homogeneous nucleation and interface controlled growth. For higher degrees of crystallinity, both growth and overall crystallization rate decreased due to compositional changes of the glassy matrix and the experimental kinetics could be described by theory if diffusion controlled growth was assumed. It was also demonstrated that the sole use of numerical fittings to analyze phase transformation kinetics, as very often reported in the literature, can give misleading interpretations. It was concluded that if proper precautions are taken the general theory predicts the glass-crystal transformation well.
47 citations
TL;DR: In this paper, the additive nature of the proeutectoid ferrite transformation was evaluated by measuring transformation kinetics partially at one temperature and after a rapid temperature change to another temperature.
Abstract: This study critically examines the principle of additivity and the reason that the proeutectoid ferrite transformation is additive. Austenite-to-proeutectoid ferrite transformation kinetics were measured under isothermal and stepped-isothermal conditions for AISI 1010 and 1020 steel grades using a dilatometer and a Gleeble 1500 thermomechanical simulator. The additive nature of the austenite-to-proeutectoid ferrite transformation was experimentally assessed by measuring transformation kinetics partially at one temperature and after a rapid temperature change to another temperature. Results of the tests on the 1010 steel showed that the proeutectoid ferrite transformation with allotriomorphic morphology is additive. Transformation kinetics were mea- sured for the 1020 steel with the ferrite morphology changing from allotriomorphic to predom- inantly Widmanstatten, and the transformation was additive. However, the stepped-isothermal test in which the ferrite was transformed and equilibrated at the first temperature and then rapidly cooled to the second temperature was not additive. The second part of the study involved de- veloping mathematical models with planar and spherical interface geometries to theoretically assess the additivity of the proeutectoid ferrite transformation. Additivity of the proeutectoid ferrite transformation was tested by predicting the ferrite growth kinetics and the associated carbon gradients under stepped-isothermal conditions. The predictions were consistent with the observed experimental additivity of the proeutectoid ferrite transformation, providing an expla- nation for this behavior, although theory would suggest ferrite reaction to be nonadditive.
47 citations
TL;DR: In this article, some novel high conductivity-high strength materials were designed in the binary Cu-Mg alloys and compared with the main Cu-based alloys, and the analysis shows that they perform equally to the best one (Cu-Be).
47 citations
TL;DR: In this paper, the authors used time-resolved hot-stage transmission optical microscopy to characterize the nucleation and growth kinetics of amorphous GeTe thin-film crystallization.
Abstract: Time‐resolved hot‐stage transmission optical microscopy is used to characterize the nucleation and growth kinetics of amorphous GeTe thin‐film crystallization. This technique provides experimental measurements of the fraction crystallized, the number of crystallites, and the crystallite size as a function of annealing time and temperature. The fraction‐crystallized data are modelled using the Johnson–Mehl–Avrami formalism to give an Avrami exponent of 4, consistent with previous measurements via time‐resolved reflection/transmission methods. Microstructural measurements provide sufficient data to deconvolute the individual contributions of nucleation and growth to this exponent. This work shows that crystallization of these films proceeds by nucleation at an increasing rate due to transient effects with isotropic two‐dimensional growth in the film plane.
47 citations