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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 comprehensive molecular dynamics study of hexagonal close-packed polycrystalline materials was performed to rationalize the inconsistencies reported in literature and guide future molecular dynamics studies.
Abstract: During the past two decades, twinning and slip in hexagonal close-packed structures have been extensively studied using molecular dynamics. However, the simulation methods and corresponding results have rendered different conclusions regarding the active twin modes and their mechanisms for nucleation and growth. The nucleation mechanisms for twinning in hexagonal close-packed polycrystalline materials are known to depend strongly on grain boundary orientations, but little is known of the exact mechanisms that occur. The variability in the experimental behavior of single crystals reported in early literature may result from the extreme sensitivity of twinning and slip to heterogeneities in the crystals and their complex dislocation cores. Therefore, both the boundary conditions and loading directions are likely to have profound effects on the mechanisms of deformation captured by molecular dynamics simulations. In an effort to rationalize the inconsistencies reported in literature and guide future molecular dynamics studies, we have performed a comprehensive molecular dynamics study on magnesium that encompasses effects of crystal orientation, boundary conditions, initial defects, and interatomic potentials. The general trends of the results support theories which advocate heterogeneous nucleation for both twinning and slip. In fact, the behavior of perfect crystals with periodic boundary conditions deviated substantially from previous experimental observations. Additionally, strong non-Schmid effects were identified and consistently correlated to non-Schmid stresses. Deviations from Schmid's law were strikingly reduced by introducing defects such as free surfaces and voids, but twinning was still influenced by non-Schmid stresses. Twin–twin interactions led to secondary twinning and nanovoids, which encouraged stress localization and damage.
114 citations
TL;DR: In this paper, it was shown that complete crystallization of small quantities of glass segregated in grain boundaries in a ceramic, e.g. hot-pressed silicon nitride, will be more difficult than crystallizing a bulk glass of the same composition.
113 citations
TL;DR: The nucleation and growth kinetics of epitaxial Ba2YCu3O7−x thin films prepared on (001) SrTiO3 by postdeposition annealing of a chemically derived intermediate layer were investigated in specimens quenched from the growth anneal as discussed by the authors.
Abstract: The nucleation and growth kinetics of epitaxial Ba2YCu3O7−x thin films prepared on (001) SrTiO3 by postdeposition annealing of a chemically derived intermediate layer were investigated in specimens quenched from the growth anneal. The films were produced by spin‐on deposition of a metal‐organic precursor solution at room temperature and ambient pressure, and subsequent postdeposition annealing to form Ba2YCu3O7−x (BYC). Integrated x‐ray intensities of reflections from the majority, c‐axis‐normal epitaxial BYC in the films were analyzed as a function of time at annealing temperature. Data collected from specimens annealed at 730 and 750 °C were consistent with upward growth of the BYC from nuclei at the substrate surface with a constant growth rate. The linear transformation kinetics suggest the growth process is controlled by molecular processes at the BYC/intermediate interface, and is not rate limited by diffusion. The activation energy for film growth along its [001] axis was estimated to be ∼5 eV. The...
113 citations
TL;DR: In this article, single phase icosahedral samples were obtained by annealing melt-spun Al 75 Cu 15 V 10 amorphous alloys and the kinetics of the icosahedron phase transformation were measured isothermally and nonisotheramally by differential scanning calorimetry and from changes in the electrical resistivity.
Abstract: Single phase icosahedral samples are obtained by annealing melt-spun Al 75 Cu 15 V 10 amorphous alloys. The kinetics of this amorphous to icosahedral phase transformation were measured isothermally and nonisotheramally by differential scanning calorimetry and from changes in the electrical resistivity. Transmission electron microscopy and energy dispersive X-ray analysis indicate that the transformation proceeds polymorphically by nucleation and growth, ruling out a “micro-quasicrystal” model of the glass in this system. A standard Johnson-Mehl-Avrami analysis of the isothermal, transformation data yields Avrami exponents in the range 2–2.5, which are inconsistent with a polymorphic transformation. These anomalous Avrami exponent arise from an inhomogeneous distribution of quenched-in nuclei. Fits are made to a kinetic model assuming a constant nucleation rate and growth on these quenched-in nuclei. An analysis of the nucleation rates obtained from these fits gives an estimate for the interfacial energy between the icosahedral phase and the glass of 0.002 J/m 2 ⩽ α ⩽ 0.015 J/m 2 , demonstrating that the short range order must be similar on both sides of the interface.
113 citations
TL;DR: A model was developed almost 20 years ago which described how precipitation during the quench affected the development of properties of aluminium alloys during subsequent aging treatment as discussed by the authors, which was the basis for an analytical process known as quench factor analysis, that was used to predict the effects of quench path on corrosion characteristics and strength.
Abstract: A model was developed almost 20 years ago which described how precipitation during the quench affected the development of properties of aluminium alloys during subsequent aging treatment. This model was the basis for an analytical process, known as quench factor analysis, that was used to predict the effects of quench path on corrosion characteristics and strength. The purpose of this paper is to provide a theoretical basis for the model and to review how quench factor analysis has been used in solving industrial problems. Several investigators have confirmed that quench factor analysis is an effective predictive method for all quenching conditions save one. The exception is when material has been quenched below the knee of the C-curve and subsequently reheated above the knee before the quench is complete. Applications include the design of quench systems, the development of quench practices which optimize combinations of high strength and low residual stress and distortion, and predictions of the...
112 citations