Retardation of grain boundary reactions in Ag-Pd-Cu alloys by additions of small amounts of other elements

The grain-boundary reactions in Ag--25 mass% Pd--10 mass% Cu alloys with 1 mass% Al, cobalt, Sn, Cr or indium, were investigated by optical microscopy, electrical resistivity, and hardness tests. Addition of Sn and Cr retarded grain-boundary reactions. The growth rate of nodules with Sn addition was 1/18 of the alloy without additions. Grain-interior reactions are accelerated with Cr, Sn and In addition, with Cr the most effective. The activation energies for the grain-interior and grain-boundary reactions are 192-196 and 144-208 kJ mol exp --1 , respectively. Additions retard the growth but not the nucleation at the grain boundary. It is concluded that elements which form stable precipitates in the grains retard the grain-boundary reaction. Graphs, Photomicrographs. 14 ref.--AA