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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: Differential scanning calorimetry has been applied extensively to the analysis of light metals, especially Al-based alloys as discussed by the authors, and is used for analysis of solid state reactions, such as precipitation, homogenisation, devitrivication and recrystallisation.
Abstract: Differential scanning calorimetry (DSC) and isothermal calorimetry have been applied extensively to the analysis of light metals, especially Al based alloys. Isothermal calorimetry and differential scanning calorimetry are used for analysis of solid state reactions, such as precipitation, homogenisation, devitrivication and recrystallisation; and solid–liquid reactions, such as incipient melting and solidification, are studied by differential scanning calorimetry. In producing repeatable calorimetry data on Al alloys, sample preparation, reproducibility and baseline drift need to be considered in detail. Calorimetry can be used effectively to study the different solid state reactions and solid–liquid reactions that occur during the main processing steps of Al based alloys (solidification, homogenisation, precipitation). Also, devitrivication of amorphous and ultrafine grained Al based powders and flakes can be studied effectively. Quantitative analysis of the kinetics of reactions is assessed through reviewing the interrelation between activation energy analysis methods, equivalent time approaches, impingement parameter approaches, mean field models for precipitation, the Johnson–Mehl–Avrami–Kolmogorov model, as well as novel models which have not yet found application in calorimetry. Differential scanning calorimetry has occasionally been used in attempts to measure the volume fractions of phases present in Al based alloys, and attempts at determining volume fractions of intermetallic phases in commercial alloys and amounts of devitrified phase in glasses are reviewed. The requirements for the validity of these quantitative applications are also reviewed.

289 citations

Journal ArticleDOI
TL;DR: In this paper, the superconducting transition temperature of YBa 2 Cu 3 O 6.41 quenched from 500°C into liquid nitrogen increases from 0 to 20 K while annealing at room temperature during the first few days following the quench.
Abstract: The superconducting transition temperature, T c , of YBa 2 Cu 3 O 6.41 quenched from 500°C into liquid nitrogen increases from 0 to 20 K while annealing at room temperature during the first few days following the quench. Using neutron powder diffraction and Rietveld refinement we show that this time-dependent increase of T c is accompanied by changes in the structural properties. The a -and c -axes contract by 0.04%, while the percentage shortening of the b -axis is three times smaller. We attribute this behavior to charge transfer between the chains and planes, with the smaller contraction along the b -axis arising from oxygen ordering in the chains. Clear evidence for this charge transfer is seen in the relevant Cu-O and Cu-Cu distances. No significant changes in the average occupancies of oxygen sites are observed. We attribute the increase in T c to local ordering of oxygen atoms around the Cu(1) atoms with no change in the average site occupancies.

288 citations

Journal ArticleDOI
TL;DR: The distribution of crystallographic orientations of the grains in a polycrystalline film can evolve through a number of kinetic processes as mentioned in this paper, and the final texture of a film depends on which texture selection mechanisms and driving forces dominate, and is different for different films, substrates, and deposition conditions.
Abstract: The distribution of crystallographic orientations of the grains in a polycrystalline film can evolve through a number of kinetic processes. Orientation evolution can occur before, during and after coalescence of islands to form a continuous film, during thickening of a film, and during post-deposition annealing. The energetic constraints leading to texture selection include surface and interface energy minimization, as well as strain-energy minimization. The final texture of a film depends on which texture-selection mechanisms and driving forces dominate, and is different for different films, substrates, and deposition conditions.

286 citations

Journal ArticleDOI
TL;DR: In this paper, a thermodynamic method has been developed to allow the prediction of isothermal transformation diagrams, starting simply from a knowledge of the chemical composition of the steel concerned, and has been shown to be capable of faithfully reproducing the critical "bay region" of time-temperature-transformation (TTT) curves.
Abstract: A thermodynamic method has been developed to allow the prediction of isothermal transformation diagrams, starting simply from a knowledge of the chemical composition of the steel concerned. The method has been extensively tested and has been shown to be capable of faithfully reproducing the critical ‘bay region’ of time–temperature–transformation (TTT) curves. The TTT diagram has been treated as being composed of two overlapping ‘C’ curves, one representing the diffusional polygonalferrite and pearlite transformations, and the other representing the displacive Widmanstatten ferrite and bainite reactions. It is possible to predict relative shifts in these component curves, as a function of alloying element content, thus making the technique potentially useful in theoretical steel design. While the analysis is formally based on Russell's theory of incubation periods, it is believed that a number of difficulties prevent a fundamental interpretation of the results.

275 citations

Journal ArticleDOI
TL;DR: In this paper, the deformation rate of polycrystalline ceramics that contain a residual glass phase is analyzed in terms of material transport through the liquid phase, where molecules are transported and deposited in the direction of the positive normal traction gradient along the interfaces.

275 citations