Book•
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: It is reported that R martensite isothermally forms with time in a solution-treated Ti(48.7)Ni(51.3) single crystal, which suggests a new mechanism for the isothermal Martensite formation, which could be applied to other metal and ceramic martensitic systems to find new phases and novel properties.
Abstract: We report that R martensite isothermally forms with time in a solution-treated Ti(48.7)Ni(51.3) single crystal. This abnormal formation originates from the growth of a short-range ordered R phase with time, i.e., the "crystallization" of strain glass. The established time-composition-temperature Ti-Ni diagram shows a time evolution of the R phase and composition-temperature phase diagram. The presence or absence of the R phase in this new diagram, as well as in other conditions (like doping Fe or aging), is explained in a unified framework of free-energy landscape. Our finding suggests a new mechanism for the isothermal martensite formation, which could be applied to other metal and ceramic martensitic systems to find new phases and novel properties.
48 citations
TL;DR: In this paper, a unified view of the shape memory effect of martensitic alloys is presented, with the group-subgroup symmetry relation between the parent and martensite phase, along with analysis of reversible twinning modes in martensites.
Abstract: The (one-way) shape memory effect is a phenomenon that when a martensitic alloy is deformed in a martensitic state it recovers its original shape upon heating to the parent phase. This is a universal effect for certain martensitic alloys. We will assess the mechanism of the effect critically and select the essential factors which govern the effect. We try to understand it from a unified view, invoking the group–subgroup symmetry relation between the parent and martensite phase, along with analysis of reversible twinning modes in martensite. By such an assessment, we will show why typical shape memory alloys, such as Ti–Ni, Cu–Al–Ni etc., exhibit good shape memory characteristics, while others, such as ferrous alloys, do not. Thus, we will show that most of the shape memory characteristics of various martensitic alloys can be understood consistently from such an approach.
48 citations
TL;DR: In this article, Austenite nucleation and growth is studied during continuous heating using three-dimensional X-ray diffraction (3-D XRD) microscopy at the European Synchrotron Radiation Facility (ESRF) (Grenoble, France).
Abstract: Austenite nucleation and growth is studied during continuous heating using three-dimensional X-ray diffraction (3-D XRD) microscopy at the European Synchrotron Radiation Facility (ESRF) (Grenoble, France). Unique in-situ observations of austenite nucleation and growth kinetics were made for two commercial medium-carbon low-alloy steels (0.21 and 0.35 wt pct carbon with an initial microstructure of ferrite and pearlite). The measured austenite volume fraction as a function of temperature shows a two-step behavior for both steel grades: it starts with a rather fast pearlite-to-austenite transformation, which is followed by a more gradual ferrite-to-austenite transformation. The austenite nucleus density exhibits similar behavior, with a sharp increase during the first stage of the transformation and a more gradual increase in the nucleus density in the second stage for the 0.21 wt pct carbon alloy. For the 0.35 wt pct carbon alloy, no new nuclei form during the second stage. Three different types of growth of austenite grains in the ferrite/pearlite matrix were observed. The combination of detailed separate observations of both nucleation and growth provides unique quantitative information on the phase transformation kinetics during heating, i.e., austenite formation from ferrite and pearlite.
48 citations
TL;DR: In this paper, a model that describes the pearlite-to-austenite transformation during continuous heating in a eutectoid steel has been developed, and the influence of structural parameters (such as the interlamellar spacing and edge length of pearlite colonies) and heating rate on the austenite formation kinetics has been experimentally studied and considered in the modeling.
Abstract: A model that describes the pearlite-to-austenite transformation during continuous heating in a eutectoid steel has been developed. The influence of structural parameters (such as the interlamellar spacing and edge length of pearlite colonies) and heating rate on the austenite formation kinetics has been experimentally studied and considered in the modeling. It has been found that the coarser the initial pearlite microstructure and the higher the heating rate, the slower the kinetics of austenite formation. Moreover, both the start and finish temperatures of the transformation slightly increase as the heating rate does, but the finish temperatures are more sensitive to that parameter. A good agreement (with an accuracy higher than 90 pct in the square correlation factor) between experimental and predicted values has been found.
48 citations
TL;DR: In this article, a glass-ceramic composition was designed and tested for use as a sealant in solid oxide fuel cell (SOFC) planar stack design and the crystallization behavior was investigated by calculating the Avrami parameter (n) and the activation energy for crystallization (Ec) was obtained.
48 citations