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The second edition of this textbook, popular amongst students and faculty alike, investigates the various causes of thermodynamic instability in metallic microstructures. Materials theoretically well designed for a particular application may prove inefficient or even useless unless stable under normal working conditions. The authors examine current experimental and theoretical understanding of the kinetics behind structural change in metals. The entire text has been updated in this new edition, and a completely new chapter on highly metastable alloys has been added. The degree to which kinetic stability of the material outweighs its thermodynamic instability is very important, and dictates the useful working life of the material. If the structure is initially produced to an optimum, such changes will degrade the properties of the material. This comprehensive and well-illustrated text, accompanied by ample references, will allow final year undergraduates, graduate students and research workers to investigate in detail the stability of microstructure in metallic systems.

This paper describes some underlying principles of multicomponent and high entropy alloys, and gives some examples of these materials. Different types of multicomponent alloy and different methods of accessing multicomponent phase space are discussed. The alloys were manufactured by conventional and high speed solidification techniques, and their macroscopic, microscopic and nanoscale structures were studied by optical, X-ray and electron microscope methods. They exhibit a variety of amorphous, quasicrystalline, dendritic and eutectic structures.Keywords: alloying strategy; amorphous alloys; fcc single phase; Gibbs phase rule; high entropy alloys; icosahedral phase; multicomponent alloys; quasicrystals; solid solubility Multicomponent Alloys Alloying StrategiesThe conventional way of developing a new material is to select the main component based upon some primary property requirement, and to use alloying additions to confer secondary properties. This strategy has led to many successful multicomponent materials with a good balance of engineering properties. Typical examples include high-temperature nickel superalloys and corrosion-resistant stainless steels. In some cases two principal components are used, such as in copper-zinc brasses or alumino-silicate refractories.Cantor [1] was the first to point out that this kind of conventional alloying strategy leads to an enormous amount of knowledge about materials based on one or sometimes two components, but little or no knowledge about materials containing several main components in approximately equal proportions. Information and understanding about alloys close to the corners and edges of a OPEN ACCESS

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