Alloying elements phase diagrams

Sodium-zinc alloys for phase diagram determination are prepared by melting the elements in glass tubes under H2- Samples of NaZujj are prepared by heating zinc for several hours above the melting point of NaZn,3 (557°C) with xs Na in alundum extraction thimbles with N2 or Ar in a steel bomb scaled with copper gaskets. Excess Na was removed by extraction with liq NHj. Both KZn,3 and KCd,2 were prepared in this manner. ... 

Binary alloys whose phase diagram shows solid solubility over a wide concentration range are particularly well suited for the study of dealloying phenomena. Figure 7.28 schematically presents the pseudo-steady state anodic polarization curve of a binary single-phase alloy AB and of its two constituents, the element B being more noble than A. Two distinct potential regions are observed, separated by the critical potential,... 

The lead—copper phase diagram (1) is shown in Figure 9. Copper is an alloying element as well as an impurity in lead. The lead—copper system has a eutectic point at 0.06% copper and 326°C. In lead refining, the copper content can thus be reduced to about 0.08% merely by cooling. Further refining requites chemical treatment. The solubiUty of copper in lead decreases to about 0.005% at 0°C. 

Heat Treatment of Steel. Steels are alloys having up to about 2% carbon in iron plus other alloying elements. The vast application of steels is mainly owing to their ability to be heat treated to produce a wide spectmm of properties. This occurs because of a crystallographic or aHotropic transformation which takes place upon quenching. This transformation and its role in heat treatment can be explained by the crystal stmcture of iron and by the appropriate phase diagram for steels (see Steel). 

Fig. 6. Effect of alloying elements on the phase diagram of titanium (a) a-stabilized system, (b) P-isomorphous system, and (c) P-eutectoid system.

Take the silica-alumina system as an example. It is convenient to treat the components as the two pure oxides SiOj and AI2O3 (instead of the three elements Si, A1 and O). Then the phase diagram is particularly simple, as shown in Fig. 16.6. There is a compound, mullite, with the composition (Si02)2 (Al203)3, which is slightly more stable than the simple solid solution, so the alloys break up into mixtures of mullite and alumina, or mullite and silica. The phase diagram has two eutectics, but is otherwise straightforward. 

Figure 2. The connected schematic binary alloy phase diagrams for the light actinides. The diagrams for Ac through U and for AmCm are estimates based upon the pure elements.

Figure 2.26. Isothermal section of the Al-Bi-Sh phase diagram at 200°C. In the triangle marked hy the asterisk, three phases (coincident with the two elements A1 and Bi together with the compound AlSh) are observed. In the other triangle two-phase alloys are formed. A few tie-lines are shown. The alloy marked hy , for instance, contains the compound AlSb together with a...

Several phase diagrams of binary alloy systems have been shown (see for instance Fig. 2.18) in which the existence of intermediate phases may be noticed. In these systems we have seen the formation of AmB phases, which generally crystallize with structures other than those of the constituent elements, and which have negligible homogeneity ranges. Thermodynamically, the composition of any such phase is variable. In a number of cases, as those exemplified in Fig. 2.19, the possible variation in composition is very small (invariant composition phases or... 

Figure 4.20. Palladium-vanadium system. In (a) the phase diagram is shown the phase sequence at 800°C is indicated. The corresponding trend of the average atomic volume is shown in (b). For pure vanadium the value of the partial atomic volume in Pd solution is indicated (Vv, as obtained by extrapolation from the Pd-rich alloys) and, as a reference, the elemental atomic volume (FatV) of the pure metal.

Phase diagrams of alkali metal alloys. The pattern of the intermetallic reactivity of these metals is shown in Fig. 5.6, where the compound formation capability with the different elements is summarized. 

Intermetallic chemistry of Be, Mg, Zn, Cd and Hg 5.12.4.1 Phase diagrams of the Be, Mg, Zn, Cd and Hg alloys. The systematics of the compound formation of these metals in their binary alloys with the different elements is summarized in Fig. 5.33. On the overall they give a rather complex picture even so a number of relationships and similarities between various pairs of metals may be singled out. To go into this point in more detail, in the same figure a comparison has also been made with the compound formation patterns of Ca and A1 which are described in 5.4 and 5.13 but are close in the Periodic Table to the metals here considered. The similarity between the Be and Zn patterns may be underlined, as also that between Be and Al, being an example of the so-called diagonal relationships presented in 4.2.2.2. 

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