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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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15 Jun 1997-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a metastable decagonal phase was solidified in largely undercooled samples of Al 74 Co2 26, and the melting temperature of the metastable D-phase was determined to be 1440 K.
Abstract: The maximum undercoolability of Al-Co melts of 72 and 74 at.% Al was studied by electromagnetic levitation technique. A metastable decagonal phase was solidified in largely undercooled samples of Al 74 Co2 26 . The melting temperature of the metastable decagonal phase was determined to be 1440 K. To identify the phases crystallized upon undercooling the melt, the as-solidified samples were analyzed with respect to their phase-structures by means of scanning and transmission electron microscopy (SEM, TEM) and X-ray diffraction (XRD), Differential thermal analysis (DTA) was employed to measure the heat of fusion δ H f of the metastable D-phase.
32 citations
TL;DR: In this article, a model that describes the development of texture during the production process of bake-hardening steel recrystallized in a batch-annealing furnace is presented.
Abstract: A model is presented that describes the development of texture during the production process of bake-hardening steel recrystallized in a batch-annealing furnace. Proper conditions are analyzed to generate a pronounced γ-fiber texture and a “pancake microstructure” that shows superior deep drawability. The γ-fiber texture is assumed to be caused by the interaction between tertiary precipitating aluminum nitride particles and the recrystallization process during heating in the furnace. Deep drawability is presented in terms of the logarithmic γ- and α-fiber X-ray intensity ratio. The computer simulation of the coupled aluminum nitride precipitation and recrystallization kinetics is based on an iterative procedure. A comparison between simulation results and available experimental data proves the ability of the model to predict the final deep drawability, taking into account the initial aluminum and nitrogen contents, the time/temperature history during slab reheating, hot rolling and coiling, the degree of cold reduction, and the heating rate during batch annealing.
32 citations
TL;DR: In this article, a new model for the overall transformation kinetics of bainite has been developed based on the displacive mechanism for the bainitic transformation, which distinguishes between the nucleation kinetics in prior austenite grain boundaries, and at tips and adjacent positions of previously formed subunits.
Abstract: A new model for the overall transformation kinetics of bainite has been developed. Based on the displacive mechanism for the bainite transformation, the model distinguishes between the nucleation kinetics of bainitic ferrite in prior austenite grain boundaries, and at tips and adjacent positions of previously formed subunits. Some geometrical aspects of the development of the transformation have been used in the modelling. The theoretical results show that the tendencies obtained with the model are in agreement with experience. The second part of this work deals with the experimental validation of this model.
32 citations
TL;DR: In this article, a theoretical analysis of published experimental data on the lengthening rate of sheaves of bainite in alloy steels is concluded that they lengthen at rates much faster than expected from paraequilibrium carbon diffusion controlled growth.
Abstract: On the basis of a theoretical analysis of published experimental data on the lengthening rate of sheaves of bainite in alloy steels, it is concluded that they lengthen at rates much faster than expected from paraequilibrium carbon diffusion controlled growth. The results are interpreted in terms of the mechanism of the bainite reaction and in the context of any solute atom–transformation interface interactions.MST/980
32 citations
TL;DR: In this article, the transformation kinetics of single-phase gel with mullite composition was studied by isothermal differential calorimetry (DSC) in temperature range from 937 to 959°C.
Abstract: Transformation kinetics of single-phase gel with mullite composition was studied by isothermal differential calorimetry (DSC) in temperature range from 937 to 959°C. Single exotherm was observed for annealing temperatures below 947°C, and two overlapped exothermic peaks were seen above this temperature. According to XRD analysis, mullite was the only phase crystallized either under non-isothermal or isothermal heat treatment. Johnson-Mehl-Avrami (JMA) equation for nucleation and growth could not describe mullite crystallization adequately, even below 947°C. Using bimodal JMA-type model, that proposes mullite crystallization in two steps, the fitting was remarkably good in the whole temperature range. Obtained kinetics data do not allow one to characterize the gel, either as typical single phase one (nucleation-controlled process with two rate constants and small apparent activation energies), or as hybrid gel (mullite formation via spinel and high apparent activation energies). The rate constants were an order of magnitude smaller than is proposed for single phase gel. The apparent activation energies, however (Ea1 = 1053 ± 51 kJ/mol, and Ea2 = 1028 ± 22 kJ/mmol, were in great discrepancy to those already cited for single phase gels, but they were in very good agreement with data evaluated for diphasic and hybrid gels. Mullite a-axis length and effective fraction of mullite that is formed in the first and second step of the process provided an insight in the mechanism of mullite crystallization. It is assumed that not the nucleation and crystallization limitations, rather the phase separation is the controlling process in mullite formation from single phase gel under applied experimental conditions.
32 citations