Thermal creep analysis of noble metal alloys for the ceramic-fused-to-metal technique.
Distortion of metal frameworks for the ceramic fused to metal technique during firing is attributed to thermal creep of the alloys. Usually thermal creep measurements are performed at constant load and constant temperature over varying time periods. Because metal frameworks for the ceramic-fused-to-metal technique are cyclically stressed, a three-point bending test for dynamic measurement of creep in a modified dilatometer was developed. Bending of 14 commercially available noble metal alloys was determined in the as-cast state, as well as after simulation of the firing process. The sag at 950 degrees C, which is the firing temperature of the ceramic, was chosen as an indicator for creep. No correlation of this value to other technical data of the alloys was observed, but it was found that sag correlates with the sum of the Au and Ag content of the alloys. A strong sag was observed with high (Au + Ag) content. The lowest sag values were found with a content in the range of 50 atom % (Au + Ag). At lower (Au + Ag) content Pd becomes the main component in the alloys, and the values for sag increased slightly. The method for dynamic measurement of creep gave reproducible results and offers a possible test for rapid qualitative creep assessment.
Department of Removable Prosthodontics, School of Dental Medicine, University of Berne, Berne, Switzerland. jens.fischer@zmk.unibe.ch
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Fischer
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Baltzer
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Fleetwood
D001672:Biocompatible Materials; D019563:Mechanics; D016876:Metal Ceramic Alloys; D013696:Temperature
D001672:Biocompatible Materials; D016876:Metal Ceramic Alloys