Solubility of nitrogen in liquid Fe-10Ti and Fe-25Ti alloys

Purpose: of the study was to determine the physicochemical characteristics of thermodynamic equilibrium in the liquid metal-gas system, where the liquid metal was a liquid Fe-Ti alloy, and the reaction gas was always a mixture of nitrogen and argon with preset chemical composition. Design/methodology/approach: In the experimental studies, the levitation metal melting technique was used, which enabled, on the one hand, the liquid metal-gas thermodynamic system appropriate to the purpose to be fabricated and, on the other hand, precise measurements to be carried out within a wide nitrogen partial pressure range from 0.0005 to 0.070 atm and in the appropriate range of metal temperature variations (1973-2273 K). The solidification of a 1 g-mass sample at a rate higher than 1000 K/s assured the complete nitrogen fixation in the solidified sample compared to the liquid-state sample. Findings: It has been established in the study by experimentally measuring the nitrogen concentration in the liquid Fe-Ti alloy with varying titanium contents under hyperbaric conditions that the solubility of nitrogen in liquid Fe-Ti alloys increases with increasing partial pressure of nitrogen in the gaseous phase, and with increasing liquid metal temperature and titanium content of the metal. Research limitations/implications: The study has found that when the intensive parameters increase above the critical values, the non-metallic phase forming on the levitating metal drop surface is a titanium nitride film, as demonstrated by X-ray analysis. Such samples were eliminated from the characteristics of nitrogen solubility in the homogeneous metallic phase. Practical implications: The collected data on the thermodynamic quantities of the liquid Fe-Ti-N alloy has enriched the autonomous thermodynamic database containing information about liquid alloys of iron with nitrogen, which is being built at Czestochowa University of Technology. Originality/value: The developed formulas seem to be valuable, because - as the relevant literature indicates -the Fe-Ti system has not been examined so far under such extreme thermodynamic conditions.