Alloy systems chemistry

Effenberg, G. and Ilyenko, S. (ed.) (2004) Landolt-Bornstein, Numerical Data and Functional Relationships in Science and Technology, Physical-Chemistry. Ternary Alloy Systems Phase Diagrams, Crystallographic and Thermodynamic Data. Critically evaluated byMSIT (Springer Verlag, Berlin). 

Alloy systems have been known to man since the Bronze Age. It is, however, only in recent times that they have been the subject of systematic studies, and in these studies no tool has proved more powerful than the technique of crystal structure analysis. Indeed, the extension of our knowledge and understanding of the properties of intermetallic systems to which it has given rise is one of the greatest achievements of crystal chemistry. Prior to the application of X-ray methods, the investigation of the properties of alloy systems was confined principally to observations of their behaviour in the liquid state, and the behaviour of the metal as a solid could be determined only by inference from these observations. Transitions in the solid state and the effect of mechanical or heat treatment could not, of course, be observed in this way, and for information on these properties the microscope and other purely physical methods had to be invoked. Even so, these methods were all more or less indirect, and it is only since the application of X-ray analysis that it has been possible to investigate directly in the solid state, under the precise conditions which are of technical interest and without damage to the specimen, the exact positions of all the atoms in the structure, and so to refer to their ultimate cause the physical and chemical properties of the alloy. 

The number of alloy systems to which X-ray methods have been applied is now sufficiently large for many of the principles of metal structural chemistry to have emerged. As always, we shall here make no attempt to review the whole of this wide field but will content ourselves with illustrating these general principles by means of a limited number of appropriately chosen examples. A general classification of binary alloys, which alone we shall consider, can conveniently be based on the... 

From an economic viewpoint, the classical determination of alloy phase diagrams is a laborious process, involving alloy preparation and heat treatment, compositional, structural, and microstructural analysis (and, even then, not yielding reliable phase boundary information at low temperatures due to kinetic limitations). While this investment is justified for alloys of major technical importance, the need for better economics has driven an effort to use alternative methods of phase discovery such as multiple source, gradient vapor deposition or sputter deposition followed by automated analysis alternatively, multicomponent diffusion couples are used to map binary or ternary alloy systems structurally and by properties (see Section 6). These techniques have been known for decades, but they have been reintroduced more recently as high-efficiency methodologies to create compositional libraries by a combinatorial approach, inspired perhaps by the recent, general introduction of combinatorial methods in chemistry. 

Factors that influence SCC response will generally affect one of four basic variables in the process the material or alloy system, the chemical service environment, the electrochemical state of the system relative to surroundings, and the state of mechanical stress. Nearly all structural alloy systems can be found susceptible to SCC under certain alloy chemistry, metallurgical condition, and service environmental conditions. SCC behavior relative to alloy system was detailed in an American Society for Metals (ASM) publication [6], for a broad range of structural alloys, and has also been covered extensively for aluminum, titanium, and high-strength steels [8]. 

Commonly both solid solutions and compounds will coexist within the same material as different phases. The stability of specific phases within a given alloy system varies with the composition and the temperature. Kinetics also determine which phases form within an alloy. Many reactions are sluggish enough that the stable phase may not form initially and the alloy may exist in metastable condition for some length of time. By using chemistry and heat treatment to control the phases formed by an alloy, metallurgists can alter the strength of materials. 

Onsager s solution to the 2D Ising model in zero field (H= 0) is one of the most celebrated results in theoretical chemistry [105] it is the first example of critical exponents. Also, the solution for the Ising model can be mapped onto the lattice gas, binary alloy and a host of other systems that have Hamiltonians that are isomorphic to the Ising model Hamiltonian. 

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