Oxygen solubility in boron-containing Ni – Co melts

Abstract

Alloys of the Ni – Co system are widely used in industry. B ron is one of the alloying components in these alloys. The study of thermodynamics of the oxygen solution in boron-containing Ni – Co melts is of considerable interest for the practice of such alloys production. Thermodynamic analysis of oxygen solutions in boron-containing Ni – Co melts has been carried out. The equilibrium constant of interaction of boron and oxygen dissolved in the nickel-cobalt melts, the activity coefficients at infinite dilution, and the interaction parameters characterizing these solutions were determined for melts of different composition at 1873 K. During interaction of boron with oxygen in Ni – Co melts, the oxide phase, in addition to B 2 O 3 , contains NiO and CoO. The values of the mole fractions of B 2 O 3 , NiO and CoO in the oxide phase for different boron concentrations in Ni – Co melts were calculated at 1873 K. In the case of nickel melt at boron contents above 0.01 %, the mole fraction of boron oxide is close to unity. As the cobalt content in the melts increases to 20 %, the mole fraction of boron oxide in the oxide phase decreases, and then practically does not change. Dependences of the oxygen solubility on the contents of cobalt and boron in the studied melts were calculated. The deoxidation ability of boron decreases slightly with increasing cobalt content up to 20 %, and then increases with increasing cobalt content in the melt. Boron contents in minimum points on the oxygen solubility curves and the corresponding minimum oxygen concentrations were determined.