X-RAY-DIFFRACTION STUDIES OF AS-CAST HIGH-PALLADIUM ALLOYS

Objectives. The purpose of this study was to use x-ray diffraction (XR D) to investigate four representative high-palladium alloys in the as- cast condition and obtain new information about the metallurgical phas es. Methods. Two Pd-Cu-Ga alloys and two Pd-Ga alloys were cast into p late-shaped specimens (20 mm x 20 mm x 1.5 mm) which were bench-cooled . Polished and etched specimens were analyzed using two different x-ra y diffractometers and CuKa radiation. Results. All four alloys exhibit ed strong XRD peaks for the face-centered cubic (fee) palladium solid solution matrix, and variations in the lattice parameter were consiste nt with alloy compositions. Comparison of the relative peak intensitie s for the alloys and the pure palladium powder standard indicated that the as-cast microstructures had preferred crystallographic orientatio n. Because the two Pd-Cu-Ga alloys contained appreciable amounts of ne ar-surface lamellar interdendritic or eutectic constituents, it was po ssible to determine previously unreported XRD peaks for the Pd2Ga phas e in these alloys. Low-intensity peaks in the Pd-Ga alloys were attrib uted to small amounts of secondary phases observed in the microstructu res. Significance. Knowledge of the metallurgical structures of these high-palladium alloys can be important for interpretation of microstru ctural observations, mechanical properties, corrosion behavior and cli nical performance.