Thermodynamic Estimation of the Phase Transformations of the Fe–Ni–Cr–Cu–Si–C System

Thermodynamic analysis of phase transformations of the multicomponent Fe–Ni–Cr–Cu–Si–C system is performed. It is of interest for the advanced metallothermic preparation technology of a wear-resistant alloy. To estimate the phase composition and structure of the alloy, computer calculations of characteristic vertical sections of the phase diagram are performed using the Thermo-Calc (TCW5 version) software; they are based on a digital simulation of phase equilibria using the CALPHAD method and the TTFe-Thermotech Fe-based Alloys Database, which includes data on chemical elements and is intended for the calculations of stable and metastable phases in multicomponent alloys. The phase transformations are considered at temperatures of 300 to 1400°C, a step of 100°C, and variable contents of Ni, Cr, Cu, Si, and C alloying elements. Vertical sections of the Fe–Ni–Cr–Cu–Si–C phase diagram are calculated, and the critical temperatures of the phase transformations of the alloy and chemical compositions of the formed phases (α, β, β2, γ, γ2, L) are determined. The thermodynamic simulation results show that, when an Fe-based alloy is alloyed, its microstructure becomes more complex and its phase composition changes; this situation takes place during gas-plasma facing. To study solidification to obtain quantitative information about the solidification stages of an alloy, the critical temperatures separating the stages, the composition and amount of precipitated phases, and the effect of temperature are determined. The temperature dependence of melt solidification exhibits a transition of nonequilibrium melt solidification to an equilibrium solidification stage at 950°C; this assumes a fine-grained structure of the coating. Thermodynamic analysis allows us to predict a ferrite–martensite structure of the coating with ledeburite inclusions during the preparation of a wear-resistant coating by metallothermic technology. The constructed vertical sections show that complete dissolution of all components in liquid occurs at ~1400°C.