Retardation of grain boundary reactions in Ag-Pd-Cu alloys by additions of small amounts of other elements
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The grain-boundary reactions in Ag-25 mass% Pd-10 mass% Cu alloys with 1 mass% aluminium, cobalt, tin, chromium or indium, were investigated by optical microscopy, electrical resistivity, and hardness tests. Addition of tin and chromium retarded grain-boundary reactions. The growth rate of nodules with tin addition was 1/18 of the alloy without additons. Grain-interior reactions are accelerated with chromium, tin and indium addition, with chromium the most effective. The activation energies for the grain-interior and grain-boundary reactions are 192 to 196 and 144 to 208 kJ mol−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.
KeywordsPolymer Aluminium Nodule Growth Rate Microscopy
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