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Ametallographic study of several alloys and of their pre-solder and post-solder joints used in dental prostheses

Pascal De March, Patrice Berthod

Prosthesis frameworks are usually the assemblage of successive alloys. One of themcan present amechanical weakness, e.g. due to internal defects, which can cause an untimely rupture. The aim of this study is to perform metallographic investigations on several parent alloys and pre- and postsolders in order to reveal a possible heterogeneity of properties, aswell as to number themetallurgical phenomena thatmay locallyweaken a framework in real situation. Eight parent alloys belonging to three different classes were investment cast. Two pieces of a same parent alloy were soldered together and the assemblage underwent a heat treatment. Internalmetallurgical health and microstructure of both alloy and solder were studied and their microhardness was measured. Internal defects were noticed in several parent alloys and solder joints, inside samples which reproduce real conditions of use. The microstructures of all parent and solder alloys were characterized, as well as the inter-diffusion zone. The pre-soldering leads to an inter-diffusion which is more extended than for post-soldering, due to a higher soldering temperature. The composition and the microstructure of the solder joint are not changed in a main part of its thickness, and its microstructure remains different from the parent alloyÂ’s one.