抄録
The age-hardening behaviour, phase transformation and related microstructural changes of an Ag-Cu-Pd-Au alloy were examined by means of hardness test, X-ray diffraction, scanning electron microscopic observations and electron probe microanalysis. By aging the solution-treated specimen, two phases of the Ag-rich alpha 1 and the Pd-containing Cu-rich alpha 2 were transformed into four phases of the Ag-rich alpha 1' and the Pd-containing Cu-rich alpha 2', the CsCl-type CuPd and the AuCuI ordered phases. Microstructure of the solution-treated specimen consisted of the Ag-rich alpha 1 matrix and the Cu-rich alpha 2 particle-like structures of various sizes and the lamellar structure of the alpha 1 and alpha 2 phases. When the peak hardness was obtained, the very fine lamellar structure consisting of the Ag-rich alpha 1' and Cu-rich alpha 2' phases was newly formed in the matrix. By further aging, the fine lamellar structure grew and coarsened apparently. The hardness increase was considered to be caused mainly by the diffusion and precipitation of Cu from the Ag-rich alpha 1 matrix, and the hardness decrease was caused by the coarsening of the fine lamellar structure. The CsCl-type CuPd and the AuCuI ordered phases did not contribute to the hardness increase.
