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Annealing study of palladium-silver dental alloys: Vickers hardness measurements and SEM microstructural observations.

Guo WH, Brantley WA, Li D, Clark WA, Monaghan P, Heshmati RH

Section of Restorative and Prosthetic Dentistry, College of Dentistry, The Ohio State University, PO Box 182357, Columbus, OH, USA, 43218-2357, brantley.1@osu.edu.

Three Pd-Ag dental alloys for metal-ceramic restorations, W-1 (Ivoclar Vivadent), Rx 91 (Pentron) and Super Star (Heraeus Kulzer), were subjected to isothermal annealing for 0.5 hr periods in a nitrogen atmosphere at temperatures from approximately 400 ( composite function) to 950 ( composite function) C. The annealing behavior was investigated by Vickers hardness measurements (1 kg load) and SEM microstructural observations. The highest Vickers hardness occurred at approximately 700 ( composite function) C for W-1 and 650 ( composite function) C for Rx 91. For Super Star, there were two peaks in hardness at approximately 500 ( composite function) and 650 ( composite function) C. Additional use of light indenting loads (25 g for W-1; 10 g for Rx 91 and Super Star) revealed that hardness variations during annealing for W-1 and Rx 91 were related to the palladium solid solution matrix phase. For Super Star, the lower-temperature peak was controlled by multi-phase regions and the higher-temperature peak by the matrix phase. While microstructural changes due to annealing were evident with the SEM for Rx 91 and Super Star, no correlation was possible for W-1 because of its finer-scale microstructure. Although commercial Pd-Ag alloys have a relatively narrow composition range, their microstructures and annealing behavior can vary because of differences in proportions of secondary elements utilized for porcelain adherence and grain refinement elements, as well as other proprietary strategies employed by the manufacturers.

Published 3 January 2007 in J Mater Sci Mater Med, 18(1): 111-8.
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