The microstructure of Co-Cr-Mo-(Nb) dental alloys

SEM and TEM investigations carried out on a model dental casting alloy cont aining 0.4% C, 30% Cr, 5% Mo and the rest Co, and a similar alloy also cont aining 1% Nb which is suitable for blending with ceramic material, have sho wn that the apparently two phase microstructure observed under the optical light microscope is in fact much more complex that at first thought. From t he energy filtered TEM pictures it was able to show that in both alloys, in addition to a block shaped a-phase, an extremely fine eutectic also exists which consists of a Co-rich solid solution together with M23C6 and M6C car bides. In addition, also arranged within the eutectic, the niobium containi ng alloy also contains extremely fine niobium carbonitrides. As a result of discovery of this extremely fine ternary eutectic, it is now possible to e xplain the extremely good casting properties of these two alloys.