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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 paper, the pyrochlore to perovskite transition in sputtered PZT thin films has been studied using SEM and XRD, and the results showed a linear growth rate for the perovsite phase, thereby indicating an interface controlled process.
Abstract: The pyrochlore to perovskite transition in sputtered PZT thin films has been studied using SEM and XRD. The films were annealed in the temperature range between 350 °C and 750 °C, and the transition temperature for pyrochlore to perovskite transition was found to be around 525 °C. Isothermal annealing was used to study the nucleation and growth kinetics of the perovskite phase. The results showed a linear growth rate for the perovskite phase, thereby indicating an interface controlled process. Also, the growth was found to be isotropic in two dimensions parallel to the plane of the substrate. The nucleation of the perovskite phase was found to be random. The effective activation energy of the perovskite transition was found to be 494 kJ/mol using Avrami’s approach.

79 citations

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TL;DR: In this paper, the effect of cooling rate on the crystallization kinetics of blends of a highmelting milk fat fraction and sunflower oil (SFO) was investigated by pulsed NMR and DSC.
Abstract: The effect of cooling rate (slow: 0.1°C/min; fast: 5.5°C/min) on the crystallization kinetics of blends of a highmelting milk fat fraction and sunflower oil (SFO) was investigated by pulsed NMR and DSC. For slow cooling rate, the majority of crystallization had already occurred by the time the set crystallization temperature had been reached. For fast cooling rate, crystallization started after the samples reached the selected crystallization temperature, and the solid fat content curves were hyperbolic. DSC scans showed that at slow cooling rates, molecular organization took place as the sample was being cooled to crystallization temperature and there was fractionation of solid solutions. For fast cooling rates, more compound crystal formation occurred and no fractionation was observed in many cases. The Avrami kinetic model was used to obtain the parameters k n and n for the samples that were rapidly cooled. The parameter k n decreased as supercooling decreased (higher crystallization temperature) and decreased with increasing SFO content. The Avrami exponent n was less than 1 for high supercoolings and close to 2 for low supercoolings, but was not affected by SFO content.

79 citations

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TL;DR: In this paper, the authors studied the microstructural evolution and kinetics of intracrystalline olivine-ringwoodite transformation in order to evaluate the importance of this mechanism in subducting lithosphere.

78 citations

Journal ArticleDOI
TL;DR: In this article, a numerical model has been developed to simulate the growth kinetics associated with this morphology, and values for the growth velocity, and numbers of surface and volume nuclei have been obtained.

78 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reported the discovery of martensitic transition in single crystals of two different organic semiconductors, and established a molecular design rule to trigger the Martensitic phase transition in organic semiconductor, showing promise for designing next generation smart multifunctional materials.
Abstract: Martensitic transition is a solid-state phase transition involving cooperative movement of atoms, mostly studied in metallurgy. The main characteristics are low transition barrier, ultrafast kinetics, and structural reversibility. They are rarely observed in molecular crystals, and hence the origin and mechanism are largely unexplored. Here we report the discovery of martensitic transition in single crystals of two different organic semiconductors. In situ microscopy, single-crystal X-ray diffraction, Raman and nuclear magnetic resonance spectroscopy, and molecular simulations combined indicate that the rotating bulky side chains trigger cooperative transition. Cooperativity enables shape memory effect in single crystals and function memory effect in thin film transistors. We establish a molecular design rule to trigger martensitic transition in organic semiconductors, showing promise for designing next-generation smart multifunctional materials.

78 citations