The influence of different heat treatments on a dental Co-Cr alloy

The change in microstructure and hardness in a cast Co-Cr alloy (type A) with a carbon content of 0.45% was studied both when the alloy was aged at temperatures between 600 degree C and 1200 degrees C and when it was isothermically heat-treated at temperatures between 800 degrees C and 1000 degrees C after solubility treatment at 1200 degrees C. Furthermore, studies were undertaken on how aging at 800 degrees C, solubility treatment at 1200 degrees C and isothermal heat treatment at 800 degrees C after solubility treatment at 1200 degrees C affected the mechanical properties. The results showed that both aging and isothermal heat treatment could change both microstructure and hardness. The changes in the mechanical properties by heat-treatment, however, did not improve the usefulness of the alloy in dentistry, principally because the elongation was reduced. The change in microstructure explained the change in hardness and in mechanical properties. It was interesting to note that the properties of a Co-Cr alloy were not affected by heat-treatment at temperatures below 600 degrees C. This means that addition of gold alloys, which are soldered to a base of Co-Cr, can be both homogenised and/or hardened without affecting the properties of the Co-Cr alloy.