Phase transformation diagrams metals

Figure 4.13 A schematic diagram of the formation of twin boundaries. (This figure appeared originally in D. A. Porter and K. E. Easterling, Phase Transformations in Metals and Alloys (London Chapman Hall, 1992) and is reproduced by permission of Springer Science + Business Media.)...

Characteristics and implementation of the treatments depend on the expected results and on the properties of the material considered a variety of processes are employed. In ferrous alloys, in steels, a eutectoid transformation plays a prominent role, and aspects described by time-temperature-transformation diagrams and martensite formation are of relevant interest. See a short presentation of these points in 5.10.4.5. Titanium alloys are an example of the formation of structures in which two phases may be present in comparable quantities. A few remarks about a and (3 Ti alloys and the relevant heat treatments have been made in 5.6.4.1.1. More generally, for the various metals, the existence of different crystal forms, their transformation temperatures, and the extension of solid-solution ranges with other metals are preliminary points in the definition of convenient heat treatments and of their effects. In the evaluation and planning of the treatments, due consideration must be given to the heating and/or cooling rate and to the diffusion processes (in pure metals and in alloys). 

The WLF equation holds over the temperature range from Tg to about + 100 K. The constants in Eq. (5.76) are related to the free volume. This is a procedure analogous to the one we used to generate time-temperature-transformation (TTT) diagrams for metallic phase transformations in Section 3.1.2.2. 

M. Hillert, The uses of Gibbs free energy-composition diagrams. In Lectures on the Theory of Phase Transformations, 2nd edn, ed. H. I. Aaronson, Warrendale, PA, The Minerals, Metals and Materials Society, 1999. 

Lanthanum and cerium form a continuous series of solid solutions as shown in fig. 1. The melting points of the pure metals have been adjusted to the accepted values (table 1) from those given with the reported lanthanum-cerium phase diagrams. Lanthanum undergoes two phase transformations on heating from the double-hexagonal close-packed form (dhep) to the face-centered cubic (fee) form at 310°C and then to the body-centered cubic (bcc) form at 865°C. Cerium exhibits only the... 

In sections 2-5 we consider the influence of hydrostatic and uniaxial pressure on the transition temperatures of magnetic phase transformations, magnetization, magnetic phase diagrams and spin structures in the lanthanide metals and their alloys, and compounds with 3d transition metals (TM) and nonmagnetic elements. Pressures causing elastic strains without nonreversible deformations are considered here. 

Rousset [30] used a model called FEM-TTT. The software, based on a model originally developed for metal solidification [45,46], is able to calculate the kinetics of the phase transformation for any thermal path, using experimental isothermal crystallization kinetics data represented by the time-temperature-transformation (TTT) diagrams and an additivity principle, in a Cartesian bidimensional... 

Phase transformations may be wrought in metal alloy systems by varying temperature, composition, and the external pressure however, temperature changes by means of heat treatments are most conveniently utilized to induce phase transformations. This corresponds to crossing a phase boundary on the composition-temperature phase diagram as an alloy of given composition is heated or cooled. 

Uwal] Uwakwen, O.N.C., Liu, Z., Kinetics and Phase Transformation Evaluation of Fe-Zn-Al Mechanically Alloyed Phases , Metall. Mater. Trans. A, 28A(3), 517-525 (1997) (Phase Diagram, Phase Relations, Experimental,, 26)... 

A molten metal alloy would normally be expected to crystallize into one or several phases. To form an amorphous, ie, glassy metal alloy from the Hquid state means that the crystallization step must be avoided during solidification. This can be understood by considering a time—temperature—transformation (TTT) diagram (Eig. 2). Nucleating phases require an iacubation time to assemble atoms through a statistical process iato the correct crystal stmcture... 

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