Effect of Hot Pressing Variables on the Microstructure, Relative Density and Hardness of Sterling Silver (Ag-Cu alloy) Powder Compacts

The purpose of this work was to investigate the influence of the hot pressing variables, namely pressure, time and temperature, on the microstructure, density and hardness in a sterling silver alloy. Powders were hot pressed under different combinations of pressures (25MPa, 35MPa and 45MPa), times (10 min, 30 min and 60 min) and temperatures (250 degrees C, 300 degrees C, 400 degrees C, 500 degrees C and 700 degrees C). The microstructures of hot pressed compacts were analyzed by the means of SEM/EDS and optical microscopy. The density and hardness of specimens were assessed. The microstructure of all specimens consisted in Cu-rich precipitates of different sizes dispersed in a Ag-rich matrix. Of the variables that were examined, only temperature produced significant (p<0.05) differences in the density and hardness of the compacts. Full density of powders compacts was achieved for temperatures above 400 degrees C, irrespective of the hot pressing time. A hardness peak (similar to 120HV) was observed for the specimens hot pressed at 400 degrees C.