They can be further classified as homogeneous (consisting of a single phase), or heterogeneous (consisting of two or more phases) or intermetallic. An alloy may be a solid solution of metal elements (a single phase, where all metallic grains (crystals) are of the same composition) or a mixture of metallic phases (two or more solutions, forming a microstructure of different crystals within the metal).
The classification of these materials depends on their composition and structure.  They can be categorized as single-phase (homogeneous), multi-phase (heterogeneous), or intermetallic compounds. An alloy can be a solid solution, where all the metal grains are of the same composition, or a mixture of metallic phases with distinct crystal structures.