Effect of Thermal Treatment on the Hardness of Low Gold Content Dental Casting Ag-Pd Alloy

Abstract The age-hardening behavior and the mechanism of an experimental low gold content casting Ag-Pd alloy were studied by means of hardness test, XRD, SEM and EPMA, The results show that the hardness of specimens isothermal-aged at 400 °C after solution treated at 900 °C for 30 min increases unidirectionally from 1540 MPa to 3160 MPa with the prolongation of time. However, the hardness of the specimens isothermal-aged at 600 °C after solution treated at 900 °C for 30 min increases quickly and reaches the maximun 2870 MPa at 2 min aging time. Then the hardness decreases unidirectionally and remains at 1600-1700 MPa from 10 to 50 min aging time. Obvious precipitation takes place in the specimens isothermal-aged at 400 and 600 °C revealed by XRD. By SEM and EPMA, the precipitation particles can be seen in the specimens aged at 600 °C for 2 min after solution treated at 900 °C for 30 min. However, the time-FWMH curve shows that the increase of hardness after isothermal-aging is closely related with coherency stain from phase transformation. It is hard to define whether the phase transformation at 400 °C makes a contribution to the change of hardness.