Peritectic-eutectic reaction

With lower temperatures, the A and B points move toward the intersection A=B in the Cu-rich region (P-A -A and E4-B). At 990-995 C the above-mentioned curves intersect each other and this temperature has to be accepted as the point of the invariant peritectic-eutectic reaction... 

Abbreviations e, eutectic melting, p, peritectic decomposition, pe, peritectic-eutectic reaction, av, availaMe for crystal growth, ltd, limited possibility for crystal growth, none, not recommended for crystal growth. 

The peritectic transformation generally has little effect on the structure, properties or corrosion resistance of steels at room temperature an exception to this occurs in the welding of certain steels, when 6-ferrite can be retained at room temperature and can affect corrosion resistance. Furthermore, since most steels contain less than about 1 -0 oC (and by far the greatest tonnage contains less than about 0-3%C) the eutectic reaction is of relevance only in relation to the structure and properties of cast irons, which generally contain 2-4%C. This discussion, therefore, will be limited to the eutectoid reaction that occurs when homogeneous austenite is cooled. 

Stoiehiometrie VN undergoes a phase transition into a tetragonal phase below 205 K. At a composition of around VNo.80, a transition into a tetragonal phase occurs at 500 °C. Two different versions of the phase diagram at temperatures below 500 °C have been reported, " one with a eutectic and one with a peritectic phase reaction between tetragonal VNo.83 and 5-VNi-x. 

Phase diagrams are the roadmaps from which the number of phases, their compositions, and their fractions can determined as a function of temperature. In general, binary-phase diagrams can be characterized as exhibiting complete or partial solid solubility between the end members. In case of the latter, they will contain one or both of the following reactions depending on the species present. The first is the eutectic reaction is which a liquid becomes saturated with respect to the end members such that at the eutectic temperature two solids precipitate out of the liquid simultaneously. The second reaction is known as the peritectic reaction in which a solid dissociates into a liquid and a second solid of a different composition at the peritectic temperature. The eutectic and peritectic transformations also have their solid state analogues, which are called eutectoid and peritectoid reactions, respectively. 

Table 3 lists the invariant reactions occurring in the system. This should be considered in conjunction with Figs. 2, 3, 4 and 5. The reaction scheme is presented in Fig. 1 according to [1987Rag]. However the two maxima presented by [1987Rag] as peritectic reactions have been corrected here for eutectic reactions C2 and C3. 

Because a peritectic transformation requires solid-state diffusion as P reacts with the liquid phase to convert to a, it tends to be more sluggish than a eutectic reaction. As the a phase builds up as a layer between the and liquid phases, solid-state... 

Figure A.4 Gibbs free energy curves for invariant phase transitions, showing an eutectic (a) and a peritectic (b) reaction between a liquid (L) and two solid phases (a and P).

Fus] and [1934Fus] proposed a quasibinary section Si-Fc4Ali3 with a peritectic reaction 1-t Fc4Ali3 Fc2Al Si3 at about 920°C and a eutectic reaction between (Si) and Fc2Al6Si3 at 850°C and 32 mass% Si. However, later works failed to confirm flic presence of such a quasibinary section and consequently it is... 

Binary Alloys. Aluminum-rich binary phase diagrams show tliree types of reaction between liquid alloy, aluminum solid solution, and otlier phases eutectic, peritectic, and monotectic. Table 16 gives representative data for reactions in tlie systems Al—Al. Diagrams are shown in Figures 10—19. Compilations of phase diagrams may be found in reference 41. 

Figure 2.10. Examples of binary systems characterized by complete mutual solubility in the liquid state and, depending on temperature and/or composition, partial solubility in the solid state and presenting (in certain composition ranges) an invariant (three-phase) reaction (eutectic in the Cu-Ag, peritectic in the Ru-Ni and Re-Co and eutectoidal in Ti-W (one) and in Th-Zr (two)).

Figure 2.13. Building blocks of binary phase diagrams examples of three-phase (invariant) reactions. In the upper part the general appearance, inside a phase diagram, of the two types of invariant equilibria is presented, that is, the so-called 1 st class (or eutectic type) and the 2nd class (or peritectic type) equilibria. In the lower part the various invariant equilibria formed by selected binary alloys for well-defined values of temperature and composition are listed. In the Hf-Ru diagram, for instance, three 1 st class equilibria may be observed, 1 (pHf) — (aHf) + HfRu (eutectoid, three solid phases involved), 2 L — (3Hf + HfRu (eutectic), 3 L —> HfRu + (Ru) (eutectic).

Figure 7,8 Gibbs free energy curves and T-X phase relations for an intermediate compound (C), totally immiscible with pure components. Column 1 Gibbs free energy relations leading to formation of two eutectic minima separated by a thermal barrier. Column 2 energy relations of a peritectic reaction (incongruent melting). To facilitate interpretation of phase stability fields, pure crystals of components 1 and 2 coexisting with crystals C are labeled y and y", respectively, in T-X diagrams same notation identifies mechanical mixtures 2-C and C-1 in G-X plots.

Pb, where retrograde solubility for the solid in equilibrium with the liquid can also occur. As a critical value of n " is approached the liquid forms its own miscibility gap and the diagram then exhibits two forms of liquid invariant reaction, the lower temperature reaction being either eutectic or peritectic, while the higher temperature reaction becomes monotectic. Examples of such systems are Cu-Pb and Cu-Tl. When n becomes even larger, the top of the liquid miscibility gap rises above scale of the graph and there is little solubility of either element in the liquid. Such a diagram is typical of Mg systems such as Mg-Fe or Mg-Mn. 

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