Phase equilibria and diffusion paths in the Ti-Al-O-N system

To provide a basis for the calculation of high-temperature phase reactions in the Ti-Al-O-N system a thermodynamic dataset using the CALPHAD method (CALculation of PKAse Diagrams) was developed. Analytical Gibbs energy descriptions for the system phases were taken from literature or optimized in this work. The solid solution series Al2TiO5- Ti3O5 (tialite) was modeled with the sublattice description (A1(+3), Ti+3, Ti+4)(2)(Al+3, Ti+3, Ti+4)(1)(O-2)(5). The nine energy parameters resulting from the applied Compound Energy Formalism could be reduced to four independent parameters. Reciprocal reactions and the condition of electroneutrality were taken into account. Based on the optimized binary and ternary phase diagrams extrapolating calculations on quaternary compositions were carried out and compared with experimental work, The results show good agreement with the phase assemblages in the microstructure of ceramics in the Ti-A1-O-N system. Additionally, the oxidation behavior of gamma -TiAl can be explained qualitatively. (C) 2001 Elsevier Science B.V. All rights reserved.