THERMODYNAMIC ANALYSIS OF THE Fe-Ti-B SYSTEM AT 1550°C

Or Rahamim Nachum Frage
Department of Material Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel

Chemical interactions between molten iron, TiB and TiB2 were analyzed by classical thermodynamic approach. Two phase Fe-TiB, Fe-TiB2 and three phase Fe-TiB -TiB2 equilibriums were considered. The Gibbs energy (J/mole) for the formation of TiB and TiB2 from pure solid Ti and B were taken from literature:

Tis + 2Bs=TiB2 ; ΔG0=-335950+25.7T ; Ti + Bs=TiB ; ΔG0=-142942+28.03T

Gibbs energies for solid-liquid transformation of Ti and B were calculated according to equations

Tis=Til ; ΔGf0(Ti)=16218-8.36T ; Bs=Bl ; ΔGf0(B)=50220-21.37T

Activity coefficient of Ti and B in a liquid Fe-Ti-B dilute solution were taken as γTi0=0.01, γB0=0.01. It was established that TiB and TiB2 cannot be together in equilibrium with molten iron. The interaction of molten Fe with TiB2 leads to its dissolution and equilibrium concentrations of Ti and B in liquid solution are xB=0.11, xTi=0.055. These concentrations are significantly lower than that needed for the formation of TiB. The results of the thermodynamic analysis were applied for development of steel-TiB2 composites.









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