Conventional alloying strategy is to select a main component for the primary property, with minor alloying additions for secondary properties. This has led to many successful materials, such as high-temperature Ni superalloys and corrosion-resistant stainless steels. We have, therefore, an enormous amount of knowledge about alloys based on one component, but little or no knowledge when several main components are mixed in near-equal proportions. Theoretical understanding is similarly restricted, based on the dilute solution approximation, ignoring non-linear correlations. We know much about alloys close to the corners and edges of multicomponent phase diagrams, with nothing known about alloys in the centre of the diagram.
This paper describes alternative alloying strategies, discusses the number of possible materials, gives examples of multicomponent alloys, particularly fcc Cantor alloys based on Fe20Cr20Mn20Co20Ni20, emphasises the multitude of local environments, and discusses alloy microstructures and properties.