Interaction between nonstoichiometric titanium carbide and Fe-C alloys

This article describes a thermodynamic analysis, and the experimental verification, of the chemical interaction between nonstoichiometric titanium carbide and molten Fe-C alloys. The calculation and the analysis of the isothermal sections of the ternary Fe-Ti-C phase diagram in the 1500°C to 1600°C temperature range show that variations in composition and in the metal-ceramic ratio can occur in the course of the TiC_x-(Fe-C) composite preparation. These changes, in particular, those of the carbon content in the interacting phases, can affect the microstructure and properties of the resulting composite. The experimental results support the predictions of the equilibrium calculations, according to which nonstoichiometric titanium carbide tends toward the stoichiometric composition by absorbing carbon dissolved in the metallic binder or by releasing titanium to the melt. The microstructural observations also support the prediction that a significant amount of the carbide phase with a low carbon content can dissolve in the melt. The results of this study suggest that it is possible to design the microstructure of both the metallic and the ceramic phases in the composite by proper choice of the carbon content in the carbide phase. This allows the mechanical properties of the composites to be designed on the basis of thermodynamic considerations.