Ageing of a Pd-35 at % Ag-25 at % Cu solid solution alloy

Abstract

A palladium-35 at % silver-25 at % copper alloy has been prepared to simulate a succesful, commercial alloy. The commercial alloy is widely used because of its good corrosion resistance and formability and the fact that it develops good wear resistance and low electrical resistivity after ageing. However, little is known about the transformations which result from heat treatment of this alloy. Thus, the laboratory prepared material was used for determination of ageing transformations by means of resistance measurements, metallography, transmission microscopy, and X-ray diffraction. The following sequence of reaction was found to occur:

$$\begin{gathered} Supersaturated \to Spinodal \to Ordering and discontinuous \hfill \\ solid solution decomposition precipitation \hfill \\ \end{gathered} $$

The transformations are quite similar to those occurring in several other solid solution systems whose initial spinodal decompositions are followed by discontinuous transformations with one or more ordered phases.