CALCULATION OF PHASE-DIAGRAMS OF INTERSTITIAL COMPOUNDS

The previously proposed order parameter functional method is considere d for application to phase equilibria in ordering nonstoichiometric in terstitial compounds MX(y). Equations are derived for calculating the ranges of temperature and composition where a disordered phase and ord ered phases exist. The ordering was taken into account for the first t ime to calculate the phase diagrams of the Zr-C, Hf-C, Nb-C and Ta-C s ystems, and the possible types of nonstoichiometric ordered carbide ph ases were determined. It is shown that superstructures of the M4X3 and M8X7 type cannot be formed in nonstoichiometric MX(y) compounds.