PHASE-RELATIONS IN THE ALUMINUM CARBIDE-ALUMINUM NITRIDE-ALUMINUM OXIDE SYSTEM

The phase diagram of the pseudobinary Al4C3-AlN system was predicted u sing thermodynamic models. It was combined with previous thermodynamic descriptions of the pseudobinary Al4C3-Al2O3 and AlN-Al2O3 systems, a nd then thermodynamic properties of the pseudoternary Al4C3-AlN-Al2O3 system were assessed by modeling the Gibbs energy of the various phase s. An ionic-liquid model was applied to the liquid phase and a compoun d-energy model was applied to the solid-solution phase (2H) that forme d between Al2OC and AlN. A series of isothermal sections of the system were calculated in the temperature range of 1000 degrees-2100 degrees C, and reasonable phase relations were established. The calculated is othermal section at 1600 degrees C showed satisfactory agreement with experimental results. The calculated liquidus projection in the Al2O3- rich corner can explain the experimental observation of the microstruc ture after solidification very well, However, the present description cannot account for the phase segregation inside the solution phase but could be modified in the future, when more experimental information w ould be available.