Age-Hardening Behavior and the Related Changes in A Silver-Copper-Palladium Alloy

Age-hardening behavior and related changes were studied to elucidate the hardening mechanism of an ag–cu–pd alloy by differential scanning calorimetry (dsc), hardness test, x-ray diffraction (xrd), scanning electron microscopic (sem) observations and energy dispersive spectrometer (eds). the results showed that hardness of the alloy was raised to 90% and 68% of its solution state value by isothermal aging at 300ᵒc and 400ᵒc, respectively. however, aging at 500ᵒc led to a decrease in the hardness of the alloy. moreover, while age hardening at 300ᵒc occurred due to coherency strains between the (111) plane of ag- rich and the (111) plane of cu3pd phases, the mechanism of aging at 400ᵒc was the formation of cu_3pd superlattice with the l1_2-type crystal structure. in contrast, reduction of cu_3pd phase and formation of cu solid solution decreased hardness during aging at 500ᵒc.