Experimental and thermodynamic study of the microstructure evolution in cobalt-base superalloys at high temperature

Experiments and thermodynamic calculations were performed on five cobalt-base superalloys containing tantalum carbide and chromium carbides in order to evaluate the accuracy of thermodynamic calculation for this alloy family. The studied quantities were the solidus temperature and the phase fractions of the different carbides observed after a long time exposure at different high temperatures. The predicted and observed phases are in good agreement. However the measured phase-fractions and melting temperatures were sometimes higher than the calculated values. The disagreement in the phase fractions can be attributed to the fact that surface fractions and volume-fractions are not necessarily equal.