A calorimetric study of thermodynamic properties for binary Cu-Ge alloys

The phase transformation temperatures and enthalpy of fusion for Cu-Ge alloys in the whole composition range are systematically measured by differential scanning calorimetry (DSC). It is found that the undercoolability of liquid Cu-Ge alloys depends mainly on the nucleation ability of primary solid phases. Those liquid alloys solidifying with the preferential nucleation of intermetallic compounds exhibit smaller undercoolings than the others with the primary α(Cu) and (Ge) solid solution phases. Microstructural observation indicates that the ξ, and ₁ intermetallic compounds display non-faceted growth mode. In Cu-Ge eutectic alloys, the ξ and phases grow into lamellar structures, whereas the ₂ and (Ge) phases form irregular eutectics. The peritectic reactions can rarely be completed, and the peritectic microstructures are usually composed of both the primary and peritectic phases.