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 ۹۰% and ۶۸% of its solution state value by isothermal aging at ۳۰۰ ◦C and ۴۰۰ ◦C, respectively. However, aging at ۵۰۰ ◦C led to a decrease in the hardness of the alloy. Moreover, while age hardening at ۳۰۰ ◦C occurred due to coherency strains between the (۱۱۱) plane of Ag-rich and the (۱۱۱) plane of Cu۳Pd phases, the mechanism of aging at ۴۰۰ ◦C was the formation of Cu۳Pd superlattice with the L۱۲-type crystal structure. In contrast, reduction of Cu۳Pd phase and formation of Cu solid solution decreased hardness during aging at ۵۰۰oC.

Keywords:

Ag-Cu-Pd alloys , Age-hardening , Scanning Electron Microscopy , X-ray diffraction