Ravi Kumar N V

Thermodynamic modelling of Ti-Zr-N system is performed using Calphad method coupled with ab initio calculations. The energies of formation of stable and metastable end-members of sublattice formulations of solid phases in Zr-N system and enthalpy of mixing of the mixed nitride (Ti, Zr)N (δ) are calculated using ab initio method. Phonon calculations are used to compute the Gibbs energies of stoichiometric ZrN and the mixed nitride δ. With the aid of experimental thermochemical and constitutional data from the literature along with the results of ab initio calculations, thermodynamic optimization is carried out to obtain the Gibbs energy model parameters.

Gibbs energy model parameters for Si-Zr-N system were obtained using Calphad approach coupled with ab initio calculations. The enthalpies of formation of α and βSi3N4 in Si-N system and Zr5Si3N end-member in Si-Zr-N system were calculated using density functional theory (DFT). The finite temperature thermodynamic properties were calculated using quasiharmonic approximation (QHA). The computed heat capacities were fitted to appropriate expressions valid down to 0 K. The ab initio thermochemical data obtained in the present work and the experimental thermochemical and constitutional data from literature were used for the thermodynamic optimization of Si-N and Si-Zr-N systems. The calculated phase equilibria and thermodynamic properties are in good agreement with the input data.

In this work we report the thermodynamic modelling of the Al-N, B-N and Al-B-N systems by the Calphad approach, making use of the ab initio calculations and the available experimental thermochemical and phase equilibria data. Gibbs energy description for the Al-B system is taken from the literature, with a modification for the model for the liquid phase. The enthalpy of formation and the heat capacity of various polymorphs of AlN and BN are estimated using the DFT and the phonon calculations, respectively. The enthalpy of mixing of the mixed nitride (Al,B)N in wurtzite and cubic structures are obtained using the SQS method. Gibbs energy of formation of the mixed nitride from the binary nitrides is also computed using the phonon calculations. These quantities along with the critically assessed thermochemical and constitutional data are used for obtaining the Gibbs energy functions of various phases in the Al-N, B-N, and Al-B-N systems. Calculated phase equilibria and thermochemical data are compared with the experimental data.