The goals of this study were to investigate the
fatigue limits of two Pd-Ag
alloys (
Ivoclar Vivadent) with differing mechanical properties and varying proportions of secondary alloying elements, examine the effect of casting porosity on
fatigue behavior, and determine the effect of casting size on microstructures and Vickers hardness. The
alloys selected were: IPS d.SIGN 59 (59.2Pd-27.9Ag-8.2Sn-2.7In-1.3Zn); and IS 64 (59.9Pd-26.0Ag-7.0Sn-2.8Au-1.8 Ga-1.5In-1.0Pt). Tension test bars, heat-treated to simulate
dental porcelain application, were subjected to cyclic loading
at 10 Hz, with R-ratio of -1 for amplitudes of compressive and tensile stress. Two replicate specimens were tested at each stress amplitude. Fracture surfaces were examined with a scanning electron microscope (SEM). Sectioned
fatigue specimens and additional cast specimens simulating copings for a maxillary central incisor restoration were also examined with the SEM, and Vickers hardness was measured using 1 kg load. Casting porosity was evaluated in sectioned
fatigue fracture specimens, using an image analysis program. The
fatigue limit (2 × 10(6) loading cycles) of IS 64 was approximately 0.20 of its 0.2% yield strength, while the
fatigue limit of d.SIGN 59 was approximately 0.25 of its 0.2% yield strength. These relatively low ratios of
fatigue limit to 0.2% yield strength are similar to those found previously for high-
palladium dental alloys, and are attributed to their complex microstructures and casting porosity. Complex
fatigue fracture surfaces with striations were observed for both
alloys. Substantial further decrease in the number of cycles for
fatigue failure only occurred when the pore size and volume percentage became excessive. While the heat-treated
alloys had equiaxed grains with precipitates, the microstructural homogenization resulting from simulated
porcelain firing differed considerably for the coping and
fatigue test specimens; the latter specimens had significantly higher values of Vickers hardness.