Characteristics of Alloys

Density is a particularly important characteristic of alloys used in rotating machinery, because centrifugal stresses increase with density. Densities of the various metals in Table 1 range from 6.1 to 19.3 g/cm. Those of iron, nickel, and cobalt-base superaHoys fall in the range 7-8.5 g/cm. Those alloys which contain the heavier elements, ie, molybdenum, tantalum, or tungsten, have correspondingly high densities. 

Figure 16 shows the charge-discharge cycle characteristics of alloys in which part of the nickel component was replaced with cobalt. Misch metal (Mm), which is a mixture of rare earth elements such as lanthanum, cerium, praseodymium, and neodymium, was used in place of lanthanum. It was found that the partial replacement of nickel with cobalt and the substi-... 

General characteristics of alloys such as those presented in Fig. 3.3 have been discussed by Fassler and Hoffmann (1999) in a paper dedicated to valence compounds at the border of intermetallics (alkali and alkaline earth metal stannides and plumbides) . Examples showing gradual transition from valence compounds to intermetallic phases and new possibilities for structural mechanisms and bonding for Sn and Pb have been discussed. Structural relationships with Zintl phases (see Chapter 4) containing discrete and linked polyhedra have been considered. See 3.12 for a few remarks on the relationships between liquid and amorphous glassy alloys. 

Table 5.67. A1 and A1 alloys in the form of castings or foundry ingots. Series codes and general characteristics of alloys grouped by major alloying element.

Density is a particularly important characteristic of alloys used in rotating machinery, because centrifugal stresses increase with density. Alloys which contain the heavier elements. i.e molybdenum, tantalum, or tungsten, have correspondingly high densities. 

These differences are due to the physicochemical characteristics of alloys and their particles. The particles from Co-Cr-Ni alloys are continuously dissolved in the organism and undergo chemical modifications by the formation of precipitates or met-allo-organic complexes which have been shown to bind Ca, and in particular phosphorus or phosphates (Black 1988 Hildebrand et al. 1988 Dorr et al. 1990). 

The versatility of engineering thermoplastics has been greatly enhanced by the development of blends and alloys. Naturally, this trend complicates the selection process, and makes simplistic judgements of material capability even less reliable. The properties and processing characteristics of alloys tend to be intermediate between those of the constituents, but good coupling technology can achieve a more useful profile than either constituent alone. Numerous examples are quoted in the application sections, but the most important varieties are these ... 

Figure 9.3 shows examples of basic grid structures which carry the active masses, with examples of size and the alloy composition. Metallurgists describe the characteristics of alloys made out of different metals by phases or temperature/ concentration diagrams. Within these, the formed phases are located metal components of different constitutions and physical condition are described depending upon the composition and temperature. 

Monel alloy K-500 is an age-hardenable alloy that combines the excellent corrosion resistance characteristics of alloy 400 with the added advantage of increased strength and hardness. Qiemical composition will be found in Table 15.3. 

Table 5.6 Mechanical characteristics of alloy HN80MTY, MONICR, and HN80M-VI before and after corrosion tests in thermal convection loop [59]...

Figure 2.16 shows the charge-discharge cycle characteristics of alloys in which part of the nickel component was replaced with cobalt. Misch metal (Mm), which is a mixture of rare earth elements such as lanthanum, cerium, praseodymium, and neodymium, was used in place of lanthanum. It was found that the partial replacement of nickel with cobalt and the substitution of the lanthanum content with Mm was very useful in improving the charge-discharge cycle life. However, such alloys have insufficient capacity, as shown in Figure 2.17 [18]. From study of the effect that their compositions had on the charge-discharge capacity, it was concluded that the best alloy elements were Mm(Ni-Co-Al-Mn)This alloy led to the commercialization of sealed nickel-M H batteries. All the battery manufacturers who use a rare earth-nickel-type alloy for the negative electrode material employ similar alloys with slightly different compositions.

The same explanation for the effect of heat treatment on the characteristics of alloys was given by Dam yanovich and Bruzik [224], who investigated alloys of platinum and palladium with gold in the electrochemical reduction of oxygen. 

The characteristics of a pressed compact are influenced by the characteristics of the powder rate and manner of pressure appHcation, maximum pressure appHed and for what period of time, shape of die cavity, temperature during compaction, additives such as lubricants and alloy agents, and die material and surface condition. The effect of various compaction variables on the pressed compact are shown in Figure 6. 

Aluminum and aluminum alloys are employed in many appHcations because of the abiHty to resist corrosion. Corrosion resistance is attributable to the tightly adherent, protective oxide film present on the surface of the products. This film is 5 —10 nm thick when formed in air if dismpted it begins to form immediately in most environments. The weathering characteristics of several common aluminum alloy sheet products used for architectural appHcations are shown in Eigure 30. The loss in strength as a result of atmospheric weathering and corrosion is small, and the rate decreases with time. The amount of... 

Biomaterials. Just as stem designs have evolved in an effort to develop an optimal combination of specifications, so have the types of metals and alloys employed in the constmction of total joint implants. Pure metals are usually too soft to be used in prosthesis. Therefore, alloys which exhibit improved characteristics of fatigue strength, tensile strength, ductihty, modulus of elasticity, hardness, resistance to corrosion, and biocompatibiUty are used. 

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