Intermetallic compound melting types

My own criticism on the theories proposed for superplasticity can be summarized in one word, electrons , or more accurately the lack of electronic consideration. This is similar to the theoretical consideration brought forward in the study of LME (liquid metal embrittlement) described in the previous chapter - no electronic consideration. As shown in Table 2, all superplastic alloys of binary system are found either at eutectic or eutectoid compositions. This is illustrated in Fig. 14 in which a few binary phase diagram involving superplastic alloys are shown. However, the people who made efforts in the formulation of theories did not consider this well-known fact important enough to incorporate into their theory formulation [24], In fact, this observation is so consistent one should ask the question of the special attributes associated with eutectic or eutectoid composition. Or the fact that the intermetallic compounds with superelastic property are all of the peritectic type. It must be emphasized that to this date there is no report of finding superplasticity in congruently-melting compounds. 

In pure titanium, the crystal structure is dose-packed hexagonal (a) up to 882°C and body-centered cubic (p) to the melting point. The addition of alloying dements alters the a—p transformation temperature. Elements that raise the transformation temperature are called a-stabilizers those that depress the transformation temperature, p-stabilizers the latter are divided into p-isomorphous and p-eutectoid types. The p-isomorphous elements have limited a-solubility and increasing additions of these dements progressively depresses the transformation temperature. The p-eutectoid elements have restricted p-solubility and form intermetallic compounds by eutectoid decomposition of the p-phase. The binary phase diagram illustrating these three types of alloy... 

When melts of some metal mixtures solidify, the alloy formed may possess a definite lattice type that is difierent from those of the pure metals. Such systems are classified as intermetallic compounds, e.g. 3-brass, CuZn. At 298 K, Cu has a ccp lattice and Zn has a structure related to an hep array, but 3-brass adopts a bcc structure. The relative proportions of the two metals are crucial to the alloy being described as an intermetallic compound. Alloys labelled brass may have variable compositions, and the a-phase is a substitutional alloy possessing the ccp structure of Cu with Zn functioning as the solute. 3-Brass exists with Cu Zn stoichiometries around 1 1, but increasing the percentage of Zn leads to a phase transition to y-brass (sometimes written as Cu5Zng, although the composition is not fixed), followed by a transition to... 

Intermetallic compounds are compounds rather than mixtures. Because they are compounds, they have definite properties and their composition cannot be varied. Unlike the atoms in substitutional and interstitial alloys, the different types of atoms in an intermetallic compound are ordered rather than randomly distributed. The ordering of atoms in an intermetallic compound generally leads to better structural stability and higher melting points than what is observed in the constituent metals. These features can be attractive for high-temperature applications. On the negative side, intermetallic compounds are often more brittle than substitutional alloys. 

Alloys are manufactured by combining the component elements in the molten state followed by cooling. If the melt is quenched (cooled rapidly), the distribution of the two types of metal atoms in the solid solution will be random the element in excess is termed the solvent, and the minor component is the solute. Slow cooling may result in a more ordered distribution of the solute atoms. The subject of alloys is not simple, and we shall introduce it only by considering the classes of substitutional and interstitial alloys, and intermetallic compounds. 

With tin the compound which possesses the highest melting temperature has either the stoichiometry (R, An)5Sn3 or (R, An)5Sn4. Considering the structures of the intermetallic compounds of tin with rare earths and actinides a clear similarity appears for the composition (R, An)Sn3 all the compounds have the AuCu3 structure type. 

Computerized Modeling of Melting Points of 1-1 Type Intermetallic Compounds between Rare Earth and Nontransition Metals... 

Table 6.7 is a data file for the modeling of the melting points of 1-1 type congruently melted intermetallic compounds between rare earth and... 

Many intermetallic compounds with MsSis type silicides, where M means transition metal elements, have high melting points above 2000°C. Their silicides could be good candidates for high temperature structural applications in the next generation because they should be useable at temperatures as high as 1500°C. 

A compound having a K-Sn ratio corresponding to KSnj is soluble in liq NHj. The low-T intermetallic KSn has a body-centered tetragonal (NaPb-type) structure There are two forms, melting at 830 and 670°C. 

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