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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 authors used differential calorimetry to monitor the process through the release of the heat of crystallization, and the classical form of the TTT curve has been directly observed for the first time for cystallizing supercooled liquids, and its movement with concentration changes has been determined.
Abstract: Using water‐in‐oil emulsion samples to avoid, for the most part, heterogeneous nucleation, the crystallization of ice from a series of aqueous LiCl solutions has been studied isothermally, using differential calorimetry to monitor the process through the release of the heat of crystallization. The classical form of the time–temperature transformation TTT curve has thereby been directly observed for the first time for cystallizing supercooled liquids, and its movement with concentration changes has been determined. The conditions of observation are such that each ∼3 μ diameter droplet is multiply nucleated during the time of observation. At temperatures well above the ‘‘nose’’ of the TTT curve, where multiple nucleation does not occur, a new phenomenon—in which the rate of crystallization increases with increasing temperature of observation—is encountered. It seems probable that this is due to some heterogeneous process perhaps involving a reaction at the water–oil–surfactant interface to account for the positive temperature coefficient. The results in the homogeneously nucleated region correlate well with the much longer time scale studies reported recently on the basis of time‐dependent conductivity measurements. Using approximate diffusivity data for water in this system, the combined crystallization data can be analyzed to yield nucleation rates which are in reasonable agreement with the results of recent small angle neutron scattering studies on this system.
51 citations
TL;DR: In this paper, the precipitation of silicon in aluminum-silicon was investigated by calorimetric analysis of liquid-quenched (LQ; rapidly solidified) and solid-quench (SQ: quenched after annealing the solid at elevated temperature) alloys.
Abstract: The precipitation of silicon in aluminum-silicon was investigated by calorimetric analysis of liquid-quenched (LQ; rapidly solidified) and solid-quenched (SQ: quenched after annealing the solid at elevated temperature) alloys. Nonisothermal annealing experiments (differential scanning calorimetry) were performed using specimens containing 1.3 to 19.1 gross at. pct Si. Initial and resulting microstructures were characterized by X-ray diffraction and transmission electron microscopy. Quantitative analysis showed that heat production in LQ alloys is due to precipitation of dissolved silicon and coarsening of silicon particles already present in the as-liquidquenched state, whereas heat production in SQ alloys can be ascribed solely to precipitation. The kinetics of silicon precipitation are affected by quenched-in excess vacancies in both LQ and SQ alloys. The grain-boundary area as a function of gross silicon content is discussed in terms of its effect on vacancy annihilation and the resulting effective activation energy.
51 citations
TL;DR: In this article, the DIT model was used to model the nucleation rate of feldspar in a laboratory decompression of hydrous silicate melt. And the authors showed that dissolved H2O content controls the spatial distribution of enthalpy and configurational entropy around incipient crystals.
Abstract: Feldspar nucleation rate data obtained by laboratory decompression of hydrous silicate melt are interpreted in view of the classical theory of nucleation (CNT) and a non-classical variation, the diffuse-interface theory (DIT). The nucleation rate data can be modeled by the CNT formalism only if the interfacial free energy (σ) is allowed to vary as a function of composition. The values thus obtained vary by a factor of four (0.024–0.100 J/m2) and decrease systematically over a sixfold increase in dissolved H2O content (0.8–4.8 wt%). This result is qualitatively consistent with the effects of dissolved H2O on the liquid-vapor interfacial free energy in haplogranite magma (Mangan and Sisson 2000) and the liquid-crystal interfacial free energy in the one-component Li-disilicate system (Davis et al. 1997).
The DIT states that the interfacial region between the bulk solid and bulk melt has thermodynamic properties intermediate between these phases, and that σ is defined as the difference between the interfacial enthalpy ( H int) and interfacial entropy ( TS int). If the DIT model is correct, the nucleation rate data for feldspar may indicate that: (1) dissolved H2O content controls the spatial distribution of enthalpy and configurational entropy around incipient crystals, and (2) the spatial gradients of these potentials diverge during devolatilization.
This study suggests that crystal nucleation studies may yield insights into the structure and thermodynamics of hydrous melts; likewise, experimental studies are important for refining a physical understanding of nucleation phenomena. Our results can be applied to quantitative numerical models of ascent-driven magma crystallization.
51 citations
TL;DR: In this paper, the structure of Zr-2.3% and Zr5.5% alloy martensites on tempering at different temperatures in the range of 350 to 600°C was studied by optical and transmission electron microscopy.
51 citations
TL;DR: The applicability of the alternative hypothesis where the transformed fraction is a state function of its variables and the rate equation is different under isothermal and non-isothermal conditions is highly questionable for any processes as mentioned in this paper.
Abstract: Kinetic parameters are usually evaluated from non-isothermal experiments by supposing the same form of the rate equation in isothermal and dynamic investigations. The capabilities and limitations of this approach will be discussed. The applicability of the alternative hypothesis where the transformed fraction is a state function of its variables and the rate equation is different under isothermal and non-isothermal conditions is highly questionable for any processes. This approach is definitely invalid for crystallization kinetics as it contradicts the formal theory of solid state transformations.
51 citations