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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 studied the influence of the polycrystalline structure of the evaporated Al, the Si-Al layer sequence, and the interface layer between the Al and Si films on the overall crystallization process.
Abstract: Aluminum-induced crystallization of amorphous silicon (a-Si) is studied using various microscopy techniques and x-ray photoelectron spectroscopy. During the isothermal annealing of subsequently deposited aluminum and a-Si films on glass, a layer exchange process is induced, while a continuous polycrystalline silicon film (poly-Si) on glass is formed within the initial metal layer and therefore displaces it. This crystallization process is conducted at temperatures ranging from 350 °C to 500 °C, significantly below the eutectic temperature of the Si–Al binary system of 577 °C. The results presented focus on the influences of the polycrystalline structure of the evaporated Al, the Si–Al layer sequence, and the interface layer between the Al and Si films on the overall crystallization process. They reveal that the larger the Al grain size of the initial polycrystalline Al layer, the larger the grain size of the final poly-Si film and the slower the entire layer exchange process. It is further shown that the layer sequence, although influencing the speed of the poly-Si formation, has little impact on the overall layer exchange process. Additionally, evidence is given that an Al oxide interface layer separates the continuous poly-Si layer from the Al, independent of the original layer sequence. The analyzed oxide interface layer remains at its position throughout the entire Al and Si layer exchange process. An existing phenomenological model of the diffusion-controlled crystallization during the layer exchange is extended to embrace the role of the parameters discussed in this paper.
207 citations
TL;DR: In this article, the status of the methods and applications of thermohydrogen processing to titanium alloys are reviewed. And the principles of thermodynamic processing, based on the hydrogen induced alterations of the phase compositions and the kinetics of phase reactions in hydrogenated Titanium alloys, are overviewed.
Abstract: Thermohydrogen processing is a technique in which hydrogen is used as a temporary alloying element in titanium alloys to control the microstructure and improve the final mechanical properties. Thermohydrogen processing can also be used to enhance the processability/fabricability of titanium products including sintering, compaction, machining, and hot working (forging, rolling, superplastic forming, etc.). In the case of near net shapes, such as castings and powder metallurgy products, thermohydrogen processing is the only method available for significant microstructural modifications and consequent enhancement in mechanical properties. This paper reviews the status of the methods and applications of thermohydrogen processing to titanium alloys. Principles of thermohydrogen processing, based on the hydrogen induced alterations of the phase compositions and the kinetics of phase reactions in hydrogenated titanium alloys, are overviewed. Stable and metastable phase diagrams of several titanium alloys...
206 citations
TL;DR: In this paper, the laser-induced crystallization behavior of GeTe-based amorphous alloy thin films has been quantitatively studied by local reflection measurements with a focused 780 nm laser.
Abstract: The laser‐induced crystallization behavior of GeTe‐based amorphous alloy thin films has been quantitatively studied by local reflection measurements with a focused 780 nm laser. The use of multiple laser pulse sequences enables the nucleation rate and crystal‐growth speed to be separately deduced, allowing the compositional variation of both these processes to be followed. This not only gives detailed information on the crystallization mechanism, but also allows the fine tuning of phase change alloy compositions for use in erasable optical recording. The differences between the as‐deposited and melt‐quenched amorphous phases are also discussed. In particular, it is shown that the crystallization speed of the as‐deposited layer can differ by over an order of magnitude from that of the melt‐quenched amorphous layer. The as‐deposited state can, however, be transformed into a modified amorphous state equivalent to that obtained by melt quenching a previously crystalline layer. This allows the determination of...
205 citations
TL;DR: In this article, the authors investigated three different modeling approaches to simulate the crystallization behavior of Ge2Sb2Te5 in optical and, very recently, electrical phase-change memories.
Abstract: We investigated three different modeling approaches to simulate the crystallization behavior of Ge2Sb2Te5 in optical and, very recently, electrical phase-change memories. The first of these models is based on the Johnson–Mehl–Avrami–Kolmogorov (JMAK) formalism to calculate the fraction of crystallized material during isothermal anneals. In the literature, this model is widely used, but parameters of the model reported by different investigators vary considerably. We have shown that these discrepancies can be attributed to the inappropriate use of the JMAK approach. In order to overcome the restrictions imposed by JMAK theory, generalizations based on classical nucleation theory have been suggested. Material parameters required by the theory, such as viscosity, diffusivity, and fusion enthalpy of Ge2Sb2Te5, have been deduced from published experiments. Uncertainty in the material parameters in combination with approximate expressions used by the classical nucleation theory, however, lead us to suggest a comprehensive model based on rate equations. Although it is more complicated, this modeling approach has yielded more favorable and reliable results. We have discussed different simulation–experiment comparisons to illustrate the capabilities of the model.
205 citations
TL;DR: In this article, the equilibria of small solid particles embedded in a solid matrix are considered, and three interface quantities are of significance; an interfacial free energy representing the work of creating the interface and two interfacial stresses.
205 citations