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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, the effect of cooling rate on the degree of undercooling of one 10 μm Sn-drop is studied and theoretical estimates on the specific feature of the heterogeneous nucleation process of the effect analyzed are developed.
Abstract: Non-adiabatic fast scanning calorimetry has been developed to in-situ measure the response of single metallic drops to temperature changes in a large range of cooling rate spanning four orders of magnitude. In particular, the effect of cooling rate on the degree of undercooling of one 10 μm Sn-drop is studied. The experimental results show that the undercooling could be increased first significantly with increasing cooling rate going over to a stage of slow increase for high cooling rates, which indicates a shelf-like dependence of undercooling level on cooling rate before and after a “crossover” at a cooling rate of about 1000 K/s where two different heterogeneous mechanisms act simultaneously. First theoretical estimates are developed on the specific feature of the heterogeneous nucleation process of the effect analyzed and possible directions of further research are anticipated.
50 citations
TL;DR: In this paper, a mathematical method is presented to obtain an isothermal transformation curve from a continuous cooling transformation (CCT) curve, which can also be used for transformations that occur during continuous heating rather than continuous cooling.
49 citations
TL;DR: In this paper, a brief introduction of thermodynamic and kinetic models for predicting weld microstructure evolution is given, and the underlying assumptions of these models, including local equilibrium at the interface and conditions, are highlighted.
Abstract: An ability to predict weld microstructure is critical for introduction of new materials, as well as, optimization of existing materials. Complexity of weld microstructure evolution is related to interaction of phase stability, multicomponent diffusion, steep temperature gradients and morphological instabilities during rapid heating and cooling. In the past two decades, computational thermodynamic and kinetic models have been developed to predict these interactions in wide range of alloys. In the first section, a brief introduction of thermodynamic and kinetic models is given. Models for free energy of solid solution and compound phases, as a function of composition and temperature, are discussed. The underlying assumptions of kinetic models, including local equilibrium at the interface and conditions, are highlighted.In the second section, adoption of these models for predicting weld microstructure evolutions is demonstrated with practical examples from structural alloys. The examples focu...
49 citations
TL;DR: By introducing a gradient microstructure into 304 austenitic steel, it is shown that a strength gradient substantially enhances the fatigue life of the material.
Abstract: Steels are heavily used in infrastructure and the transportation industry, and enhancing their fatigue resistance is a major challenge in materials engineering. In this study, by introducing a gradient microstructure into 304 austenitic steel, which is one of the most widely used types of stainless steel, we show that a strength gradient substantially enhances the fatigue life of the material. Pre-notched samples with negative strength gradients in front of the notch’s tip endure many more fatigue cycles than do samples with positive strength gradients during the crack initiation stage, and samples with either type of gradient perform better than do gradient-free samples with the same average yield strength. However, as a crack grows, samples with positive strength gradients exhibit better resistance to fatigue crack propagation than do samples with negative gradients or no gradient. This study demonstrates a simple and promising strategy for using gradient structures to enhance the fatigue resistance of materials and complements related studies of strength and ductility.
49 citations
15 Nov 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the addition of 3-wt% ruthenium (Ru) has been found to improve the creep rupture life of Ni-based superalloy under both conditions of 1100 −C/150 −MPa and 1000 −C /310−MPa.
Abstract: The addition of 3 wt% ruthenium (Ru) has been found to improve the creep rupture lives of a single crystal Ni-based superalloy under both conditions of 1100 °C/150 MPa and 1000 °C/310 MPa. Creep curve analysis indicates that the creep mechanisms are different from each condition. The improvement of creep rupture lives by 3 wt% Ru addition is discussed not only from the view of dislocation movement but also the γ′ phase evolution. The change of γ/γ′ lattice misfit in the initial microstructure is believed to be the key role of Ru on the high-temperature creep deformation. The larger negative lattice misfit caused by an addition of 3 wt% Ru induces smaller and more regular γ′ particles in the initial state, as well as denser dislocation networks at the γ/γ′ interface during creep. These two aspects are crucial to the high-temperature creep rupture life. In addition, a little topologically close-packed (TCP) phases are observed after creep rupture in the two experimental alloys.
49 citations