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

Abstract

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.