Study of the Influence of Silver Addition on the Order-disorder Transformations in Cu-Au System

The order disorder transition takes a very important place because of its influence on the physical and mechanical characteristics of metals. The copper-gold system provides a classical example of structure which has been classified as long period superlattice. The addition of silver in Au-Cu binary system leads to the appearance of ordered regions and two-phase decomposition region. Thus, the ternary Au-Ag-Cu system undergoes different transformations such as ordering, precipitation and spinodal decomposition depending on the composition of alloy. In this work we study the effect of addition of Ag on order-disorder transformation in Au-Cu system. We have choose the following alloys: Au-25 wt. % Cu and Au-50 wt. % Cu as reference alloys and Au-18 wt. % Ag-7 wt. % Cu and Au-35 wt. % Ag-15 wt. % Cu, To characterize the structural evolution, we have used dilatometry and differential scanning calorimetry (DSC). The obtained results enable us to show that the Ag addition leads to the decrease of ordering temperature and the apparition of other transition in comparison with the reference alloys.