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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: The phenomenological theory of martensite crystallography is based on the observation that the habit plane is an invariant plane in which all lines in it are neither distorted nor rotated by the displacement vector of the invariant planes strain this article.
Abstract: The phenomenological theory of martensite crystallography is based on the observation that the habit plane is an invariant plane in which all lines in it are neither distorted nor rotated by the displacement vector of the invariant plane strain. The structural change is effected by a Bain deformation which follows intuitively from the orientation relationship and through which atomic interchanges do not occur. A lattice invariant deformation is also incorporated to insure that the martensite-parent interface is semicoherent and glissile. These factors and the orientation relationship as well are uniquely interrelated within the theoretical framework and must be so for any transformation alleged to follow the theory.
66 citations
04 Oct 2013
65 citations
01 Sep 1974-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, a series of iron-platinum alloys containing 25 or 27 at. pct platinum and with ordering of the γ-phase varying from substantial disorder to nearly complete order have been thermally cycled between 25°C and - 196°C.
Abstract: A series of iron-platinum alloys containing 25 or 27 at. pct platinum and with ordering of the γ-phase varying from substantial disorder to nearly complete order have been thermally cycled between 25°C and - 196°C. The kinetics of the γ⇌α transformations, the hysteresis revealed by electrical resistanceJtemperature plots, the thermoelastic growth and the reappearance of an identical microstructure after thermal cycling (the microstructural memory effect) were studied as a function of the ordering of the γ-phase. Thermoelastic growth does not appear to be affected by changes in the degree of order of partially ordered specimens but the microstructural memory was imperfect in the most highly ordered specimen examined. In agreement with earlier observations by Dunne and Wayman,3 the difference between the As and Ms temperatures and the hysteresis decrease markedly as the order is increased. It is shown by transmission electron microscopy that in all but the most highly-ordered specimens the α- γ transformation produces plates of austenite with a high density of dislocations. These plates are separated from the surrounding untransformed parent austenite by arrays of dislocation loops lying in the interfaces between untransformed parent austenite and the original martensite plates. All the dislocations have a Burgers vector direction which is the same as that of the usual slip dislocation in austenite. Such dislocations lying in a habit plane must be sessile. In the well-ordered specimen dislocation pairs, typical of glide dislocations in a crystal with long-range order, were formed in the austenite formed by the reverse transformation. These dislocations were segregated into roughly plate-like clusters, but the number of clusters in unit volume was appreciably less than the number of original plates of martensite. In this case, no arrays of sessile loops of dislocations mark the locations of the original martensite-austenite interface. It is deduced from the microscopic and kinetic results that the inherited nuclei responsible for the microstructural memory effect are located in localized volumes of highly dislocated austenite formed by the α- γ transformation. No unique dislocation configurations which could be associated with specific nuclei were found. The effects of ordering on the various kinetic effects and the microstructural memory are discussed in terms of the concept of inherited nuclei, the change of the flow stress of the γ-phase with ordering and temperature and the variation of To and the transformation driving-force with ordering.
65 citations
TL;DR: In this paper, diphasic yttrium-aluminum garnet (Y3Al5O12, YAG) sol sols were made by hydrolysis of aluminum and Yttrium isopropoxides, and they were gelled across TEM grids to make films.
Abstract: Diphasic yttrium-aluminum garnet (Y3Al5O12, YAG) sols were made by hydrolysis of aluminum and yttrium isopropoxides. The sols were gelled across TEM grids to make films. The films were heat-treated up to 1550 °C for as long as 300 h. Heat-treatments of bulk gel were also done. Microstructure and phase evolution were observed by TEM. Some observations were done in situ in a TEM hot-stage. YAG fraction and grain size, matrix grain size, nuclei/area, and film thickness were measured. Bulk samples were characterized by x-ray, DTA, and TGA. Yttrium-aluminum monoclinic (YAM) and transition alumina appeared at 800 °C. YAG nucleated between 800 °C and 950 °C. Nucleation was weakly correlated with the transient presence of YAlO3 garnet, and was eventually site-saturated at 0.3/μm3. The change in grain growth rate of the YAM and transition alumina matrix correlated with the change in the growth rate of YAG. Between 850 °C and 1000 °C YAG growth had t1/2 dependence and 280 kJ/mole activation energy. Below 850 °C nucleation was continuous, and growth had t0.85 dependence. Above 1000 °C YAG growth had t1/4 dependence, and the matrix grains coarsened with t1/4 dependence. Thicker films reacted faster because the nuclei/area and the growth rate after nucleation scaled with thickness. YAG growth was accompanied by formation of 20–100 nm subgrains. In the late stages of matrix grain coarsening there was also some reaction to YAG by a different process. Nucleation and growth kinetics are compared with other systems. Possible mechanisms are discussed.
65 citations
TL;DR: In this article, the number and sizes of the principle sphere configurations at saddle points and interstitials are determined for three model structures: (1) the Finney hard sphere model, (2) the finney model relaxed under a Morse potential, and (3) the Scott model relaxed under a Lennard-Jones potential.
Abstract: Interstitial diffusion in dense random packed structures is discussed and the literature on the description of interstitial space in these structures reviewed. The numbers and sizes of the principle sphere configurations at saddle points and interstitials are determined for three model structures: (1) the Finney hard sphere model; (2) the Finney model relaxed under a Morse potential; and (3) the Scott model relaxed under a Lennard—Jones potential. The results obtained are in good agreement with recent work by other authors. Finally, the implications of the results for interstitial diffusion are discussed and crude estimates for the activation energy obtained.
65 citations