The thermodynamic properties of melts and phase equilibria in the iron-boron system. Transition of liquid Fe-B melts into the amorphous state

The vapor composition and the thermodynamic properties of iron-boron alloys were studied by Knudsen mass spectrometry in the temperature and composition ranges 1473-1854 K and 9.7-73.0 at. % B. The mass spectra of saturated vapor contained the Fe+ and B+ ion peaks, which was evidence of a simple vapor composition. A representative array of data on component activities including more than 400 values at various compositions and/or temperatures were collected. The concentration and temperature dependences of the thermodynamic properties of Fe-B melts were approximated by the model of associated solutions on the assumption of the formation of FeB and Fe3B groups. The model, the experimental data, and the thermodynamic properties of iron borides determined earlier were used to calculate phase equilibria in the Fe-B system. The calculation results were in close agreement with independent data obtained by physicochemical analysis methods. The suggested thermodynamic description of melts and iron borides was used to analyze the thermodynamic and kinetic (viscosity) parameters of transition of liquid Fe-B compositions into the amorphous state. Using the concept of association allowed us to quantitatively interpret the behavior of these characteristics and the relative stabilities of the liquid, crystalline, and amorphous states.