Thermodynamic properties and phase equilibria in the iron–boron system. Transition of the Fe–B melt into the amorphous state

Abstract

The vapour composition and the thermodynamic properties of liquid and crystalline iron–boron alloys have been investigated by Knudsen mass spectrometry over the temperature and concentration intervals 1449–1854 K and 9.7–73.0 mol% B, respectively. The mass spectra of the saturated vapour contain Fe⁺ and B⁺ ion peaks, which is indicative of its simple composition. The thermodynamic functions of formation of FeB and Fe₂B iron borides from γ-Fe and rhombohedral boron have been computed using the experimental data. The concentration and temperature dependencies of the thermodynamic properties of the Fe–B melts have been approximated using the associated-solution model under the assumption that FeB and Fe₃B complexes exist in the melt. The phase equilibria computed on the basis of the obtained thermodynamic properties and the developed model are shown to agree with available experimental information. The suggested complete thermodynamic description of the iron–boron system has been applied to analyse the thermodynamic and kinetic (viscosity) characteristics of transition of liquid Fe–B compositions into the amorphous state. The association concept allows quantitative interpretation of the behaviour of these properties and the relative stability of the liquid, crystalline and amorphous states.