Multiple-phase alloys

Alloys are classified broadly in two categories, single-phase alloys and multiple-phase alloys. A phase is characterized by having a homogeneous composition on a macroscopic scale, a uniform structure, and a distinct interface with any other phase present. The coexistence of ice, liquid water, and water vapor meets the criteria of composition and structure, but distinct boundaries exist between the states, so there are three phases present. When liquid metals are combined, there is usually some limit to the solubility of one metal in another. An exception to this is the liquid mixture of copper and nickel, which forms a solution of any composition between pure copper and pure nickel. The molten metals are completely miscible. When the mixture is cooled, a solid results that has a random distribution of both types of atoms in an fee structure. This single solid phase thus constitutes a solid solution of the two metals, so it meets the criteria for a single-phase alloy. 

Alloys of copper and zinc can be obtained by combining the molten metals. However, zinc is soluble in copper up to only about 40% (of the total). When the content of a copper/zinc alloy contains less than 40% zinc, cooling the liquid mixture results in the formation of a solid solution in which Zn and Cu atoms are uniformly distributed in an fee lattice. When the mixture contains more than 40% zinc, cooling the liquid mixture results in the formation of a compound having the composition CuZn. The solid alloy consists of two phases, one of which is the compound CuZn and the other is a solid solution that contains Cu with approximately 40% Zn dissolved in it. This type of alloy is known as a two-phase alloy, but many alloys contain more than three phases (multiple-phase alloys). 

Alloys are classified broadly in two categories, single-phase alloys and multiple-phase alloys. A phase is characterized by having a homogeneous composition on a macroscopic scale, a uniform structure, and a distinct interface with any other phase present. The coexistence of ice, liquid water, and water vapor meets the criteria of composition and structure, and distinct boundaries exist between the states so there are three phases present. 

These include liquid-liquid interfaces (micelles and emulsions), liquid-solid interfaces (corrosion, bonding, surface wetting, transfer of electrons and atoms from one phase to anodier), chemical and physical vapor deposition (semiconductor industry, coatings), and influence of chemistry on the thermomechanical properties of materials, particularly defect dislocation in metal alloys complex reactions in multiple phases over multiple time scales. Solution properties of complex solvents and mixtures (suspending asphaltenes or soot in oil, polyelectrolytes, free energy of solvation theology), composites (nonlinear mechanics, fracture mechanics), metal alloys, and ceramics. 

Crystallization of Blends The first polymer blend was made from two polymeric mbbers in 1846, but polymer blend technology and a scientific understanding of the underlying principles controlling the compatibility (or lack of) in polymer mixtures (alloys as they have been named recently) has taken place only in the latter part of the current century. Many blends are non-crystalline but our interest in this document is focused on the kinetics of phase transformations of binary and ternary systems that receives more attention annually. Some of these systems can be very complicated, often comprised of multiple phases that m involve homopolymers, copolymers, mesophases and the like. Polymorphism and even isomorphism may occur... 

Alloys. Alloys consist of two or mote elements of different vapor pressures and hence different evaporation rates. As a result, the vapor phase and therefore the deposit constantiy vary in compositions. This problem can be solved by multiple sources or a single rod- or wire-fed electron beam source fed with the alloy. These solutions apply equally to evaporation or ion-plating processes. 

Fig. 12. X-ray diffraction pattern of a Ni75Cu25 alloy (a) completely transformed into its -hydride (0 NiCuH), (b) after a partial hydride decomposition, alloy peaks appearing, (c) after a complete hydride decomposition, arrows pointing to the rich in copper alloy phase desegregated from the initial alloy after a multiple hydrogen absorption-desorption treatment. The peaks had been revealed after the disappearance of the hydride peaks. After Palczewska and Majchrzak (48),...

Besides the multiplicity of defects that can be envisaged, there is a wide range of host solid phases within which such defects can reside. The differences between an alloy, a metallic sulfide, a crystalline fluoride, or a silicate glass are significant from... 

One of the consequences of accepting the presence of multiple magnetic states is an additional contribution to the entropy and, therefore, several authors have considered the inclusion of multiple states in their description of low-temperature phase transformations in Fe and its alloys (Kaufman et al. 1963, Miodownik 1970, Bendick and Pepperhoff 1978). However, most authors have, in the end, preferred to describe the magnetic effects in Fe using more conventional temperature-independent values for the magnetic moments of the relevant phases. This is partly linked to the absence of any provision for the necessary formalism in current... 

The procedure described above is simple to model in a computer programme and has a number of significant advantages (1) The Scheil equation is only applicable to binary alloys and is not easily derived with multiple k values, which would be necessary for a multi-component alloy. A calculation as described above can be applied to an alloy with any number of elements. (2) The partition coefficients need not be constant, which is a prerequisite of the Scheil equation . (3) The Scheil equation carmot take into account other phases which may form during such a solidification process. This is handled straightforwardly by the above calculation route. 

In most materials selection processes, it is virtually impossible to make materials choices independent of the product shape. This includes not only the macroscopic, or bulk, shape of the object such as hammer or pressure relief valve, but also the internal or microscopic shape, such as a honeycomb structure or a continuous-fiber-reinforced composite. Shape is so important because in order to achieve it, the material must be subjected to a specific processing step. In Chapter 7, we saw how even simple objects made from a single-phase metal alloy could be formed by multiple processes such as casting or forging, and how these processing steps can affect the ultimate properties of the material. As illustrated in Figure 8.6, function dictates the choice of... 

In the area of specialty polymers, we are seeing an explosion of new polymer blends, alloys, and composites. The properties of novel polymer alloys, for example, are significantly better than those of the materials from which they are blended, but many aspects of these alloys are not well understood. Most of the materials consist of multiple polymer phases. But there is still uncertainty as to the desired characteristics and size of the polymer domains and the mechanisms by which forces are transferred through the material. All of these questions will benefit from the chemical engineering approach. 

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