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The theory of transformations in metals and alloys

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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Journal ArticleDOI
TL;DR: It is reported that the vast majority of deformation twins in nanocrystalline Al, Ni, and Cu, contrary to popular belief, yield zero net macroscopic strain.
Abstract: Macroscopic strain was hitherto considered a necessary corollary of deformation twinning in coarse-grained metals. Recently, twinning has been found to be a preeminent deformation mechanism in nanocrystalline face-centered-cubic (fcc) metals with medium-to-high stacking fault energies. Here we report a surprising discovery that the vast majority of deformation twins in nanocrystalline Al, Ni, and Cu, contrary to popular belief, yield zero net macroscopic strain. We propose a new twinning mechanism, random activation of partials, to explain this unusual phenomenon. The random activation of partials mechanism appears to be the most plausible mechanism and may be unique to nanocrystalline fcc metals with implications for their deformation behavior and mechanical properties.

161 citations

01 Jan 2012
TL;DR: In this paper, the growth of 18R and 14H within the α-Mg matrix was examined using conventional transmission electron microscopy and atomic resolution high-angle annular dark-field scanning transmission electron microscope.
Abstract: Abstract The growth of and transformation between 18R and 14H phases in a Mg–8Y–2Zn–0.6Zr (wt.%) alloy have been examined using conventional transmission electron microscopy and atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The growth of both 18R and 14H within the α-Mg matrix occurs via a ledge mechanism, with the thickness of the particle increasing by the height of the ledge as it propagates. The unit height of the growth ledges or disconnections is 1.563 nm for 18R and 1.824 nm for 14H, and the displacement vector is a / 3 〈 1 ¯ 0 1 0 〉 α . 18R transforms in-situ to 14H during prolonged heat treatment at 500 °C. The 18R to 14H transformation is shown to occur most readily in regions where the 18R structure has irregularities in the building block stacking, in particular where a pair of adjacent building blocks is separated by four rather than two α-Mg layers. It is proposed that the diffusional-displacive 18R to 14H transformation rate is controlled by the diffusion rate of Y and Zn atoms into the segregation layers.

159 citations

Journal ArticleDOI
TL;DR: The status of knowledge of phase nucleation and growth processes on a solid surface in one and multicomponent systems is surveyed in this article, where the formation kinetics and subsequent evolution of new phase islands are investigated.
Abstract: The status of knowledge of phase nucleation and growth processes on a solid surface in one- and multicomponent systems is surveyed. The formation kinetics and subsequent evolution of new phase islands are investigated. Models for film growth from the vapor and solution-melt are analyzed which include island distribution by size, the degree of coalescence, island orientation, morphological stability, etc. The Ostwald ripening of the ensembles of multicomponent islands of a new phase is considered for both the isothermal and non-isothermal cases and nonlinear effects involved in the growth of continuous structures are examined. The problem of controllable growth of new phase layers is discussed.

159 citations

Journal ArticleDOI
TL;DR: The geometric properties of polygranular microstructures of the Johnson-Mehl cellular types have been studied through computer simulation as mentioned in this paper, and their geometric features have been characterized through a combination of analytic and computer simulation studies.

159 citations

Journal ArticleDOI
TL;DR: The physical stability of solid dispersions as a function of RH is highly dependent on the polymer used to form the solid dispersion, with PVP-containing dispersions being much less physically stable at high RH than HPMCAS- containing dispersions.
Abstract: Purpose The objective of this study was to investigate the effects of polymer type and storage relative humidity (RH) on the crystallization kinetics of felodipine from amorphous solid dispersions

158 citations