Transformation In Binary Alloys Research Articles

Theory of order-disorder and order-order transformations in binary alloys with B.C.C. lattice—II: Phase diagrams

The calculations of the order-disorder phase diagrams and phase equilibrium between the superstructures B2(CuZn), DO 3(Fe 3Al) and B32(NaTl) were carried out by Kikuchi's method with the account of atomic interaction and the short-range order in the first two coordination spheres. The dependence of the phase diagram on the relation of the ordering energy inthe second coordination sphere v 2 to the ordering energy in the first coordination sphere v 1 is discussed. In many respects the results are essentially different from those known earlier and are in agreement with experiment. This gives new opportunities to the classical ordering theory for a quantitative description of some binary systems.

Theory of order-disorder and order-order transformations in binary alloys with B.C.C. lattice. I. Free energy and phase equilibrium equations

Nous avons étudié des alliages fer-aluminium dont la teneur en Al était comprise entre 0 et 44 at.%. Leurs propriétés mécaniques ont été mesurées entre l'ambiante et 700°C et parallélement nous avons observé leur structure au microscope électronique. Un maximum de la limite élastique a été décelé au voisinage de la température critique d'ordre DO3. Plusieurs mécanismes ont déjà été proposés pour rendre compte de ce maximum: nous les avons rapidement passés en revue et critiqués. On observe également un maximum de la limite élastique isotherme au voisinage de la composition Fe3Al. Ce dernier maximum est interprété comme provenant du passage des dislocations simples aux dislocations doubles.Enfin nous avons pu faire quelques observations concernant la nature des transformations phase DO3-phase désordonnée et phase DO3-phase B2.We have studied iron—aluminium alloys whose aluminium content was between 0 and 44 at.%. The mechanical properties have been tested between 20°C and 400°C and the structure has been observed by means of electron microscopy.A maximum in yield stress is detected near the DO3 critical temperature. Several mechanisms have been previously proposed to explain this maximum. They are critically examined according to the electron microscopy results.A maximum in isothermal yield stress is also observed near the Fe3Al composition. This latter maximum is thought to result from a change from single dislocations to double ones.Several observations have been made about the nature of the following transformations: DO3 phase ⇌ disordered phase and DO3 phase ⇌ B2 phase.Die mechanischen Eigenschaften von Eisen—Aluminium-Legierungen mit 0 bis 44 At.-% Al wurden zwischen Raumtemperatur und 700°C gemessen. Parallel dazu wurde ihre Struktur im Elektronenmikroskop beobachtet. In der Nähe der kritischen Temperatur der der Struktur DO3 wurde ein Maximum der Streckgrenze festgestellt. Mehrere bereits vorgeschlagene Mechanismen zur Erklärung dieses Maximums werden kurz zusammengestellt und kritisch diskutiert. Ein weiteres Maximum der Streckgrenze wird isotherm nahe der Zusammensetzung Fe3Al beobachtet. Das letztere Maximum wird dem Übergang einfacher Versetzungen in Doppelversetzungen zugeschrieben.Schlieβlich konnten einige Beobachtungen zu den Umwandlungen der Struktur DO3 in die ungeordnete Phase und in die B2-Phase gemacht werden.

Experimental observations of continuous transformations in binary alloys

Experimental observations of continuous transformations in binary alloys

Classification of binary alloys and their phase diagrams by the type of transformations occurring in them

1. Binary alloys crystallizing from homogeneous liquid melts can be divided into alloys of the eutectic, peritectic, and megotectic type, depending on the type of the transformations and structures occurring. Each of them can have complete, limited, or no solubility in the solid state, i.e., have a homogeneous solid solution, a mixture of solid solutions with limited solubility, or a mixture of pure components. 2. Limited solubility of the components in the liquid state causes the development of a mixture of two equilibrium liquid solutions with different concentrations. Crystallization begins either in one of the liquid phases (monotectic transformation) or in both liquid solutions simultaneously (syntectic transformation) and continues until the disappearance of one of the liquid phases. Further crystallization of the homogeneous liquid solution occurs by the usual means (of the eutectic, peritectic, or megotetic type). 3. The presence of allotropic modifications makes the diagrams “multilevel,” and the formation of chemical compounds or intermediate phases makes the diagrams “multisectional.” Each “level” or “section” of the complex diagram is one of the basic phase diagrams shown in Fig. 3. 4. The simplest types of diagrams described here (Fig. 3) are the fundamental building blocks from which is built the whole theory of transformations in binary alloys and their phase diagrams.