Metallurgical Aspects of High-palladium Alloys
Department of Occlusal Reconstruction, School of Dentistry, University of Nijmegen, The Netherlands.Journal of Dental Research (Impact Factor: 4.14). 11/1988; 67(10):1307-11. DOI: 10.1177/00220345880670101201
Nine commercial high-Pd alloys were investigated. Microstructure and phase composition were screened by x-ray diffraction, light microscopy, and an electron microprobe. After being etched, some high-Pd alloys revealed dendritic structures. The others showed a more homogeneous structure with distinct grain boundaries. Etching was necessary to reveal distinct structures, though the overall etching effect turned out to be limited. On unetched specimens, only a slight chemical heterogeneity could be determined. Except for one alloy, the systems turned out to have complex multi-phase structures. The main face-centered-cubic (fcc) phase was Pd-based. As secondary phases, body-centered-cubic (bcc) and/or simple cubic ones were detected. The latter phases were similar to a Cu3Ga and PdGa intermetallic compound, respectively. Face-centered-tetragonal (fct) structures reported by other investigators were not found.
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ABSTRACT: The corrosion behaviour of eight commercial high-Pd alloys was investigated and compared to that of Pd-Ag systems. They were tested with standard potentiodynamic techniques in 0.9 per cent saline solution and an artificial saliva. The corrosion behaviour of the high-Pd alloys was satisfactory and essentially equivalent. In more systems anodic overloading in 0.9 per cent saline in this alloy group seemed to be superior compared to the Pd-Ag alloy group. Within the high-Pd alloy systems compositional and constitutional variations were apparently too small to result in substantial electrochemical effects.
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ABSTRACT: High-palladium alloys for metal ceramic restorations, based on the Pd-Cu-Ga and Pd-Ga systems, were introduced to the dental profession during the past decade. These alloys have become increasingly popular because they are much less expensive than the gold-based alloys, and recently marketed high-palladium alloy compositions have excellent mechanical properties. A summary of the important melting and casting considerations for these somewhat technique-sensitive alloys is presented together with an overview of important dental materials science aspects and the results of a dental laboratory survey. A maxillary central incisor coping was chosen as the clinically appropriate specimen shape, and the gas-oxygen torch melting technique was found to produce castings with clinically acceptable levels of marginal sharpness and little evidence of microporosity. The etched as-cast high-palladium alloys exhibited fine-scale multiphase microstructures, and a noteworthy finding was that relative proportions of the microstructural constituents frequently varied for thin versus thick sections of the cast specimens.