The standard alloys discussed in Chapter 9 were relatively dilute, solid-solution alloys of transition elements which, with one exception, contain a maximum of about 20 At% of alloying additions. The alloys considered in this chapter contain up to about 60 At% of noble-metal, substitutional additions to the lattice of the transition-metal base. Three alloy systems of this kind have been studied: copper-nickel, silver-palladium, and gold-palladium [1–5]. Each of these systems shows complete solid solubility (with no intermediate phases) below the solidus.