3. Phase A phase is a homogeneous part of the material in which no abrupt change in composition, structure and properties occurs An alloy may be single phase or multi-phase material 4. Structure Structure is a general term for the combination of atom arrangement including the types amounts and distribution of all types of material as well as grain size, defect etc3. Phase A phase is a homogeneous part of the material in which no abrupt change in composition, structure and properties occurs. An alloy may be single phase or multi-phase material. 4. Structure Structure is a general term for the combination of atom arrangement including the types amounts and distribution of all types of material as well as grain size, defect etc