Construction of a mathematical model of turbulent heat and mass transfer processes for the case of electron beam melting of titanium alloy casts

This paper describes a mathematical model built for turbulent heat and mass transfer processes in the case of electron beam melting of titanium alloy ingots. The object of research is the conditions that ensure the quality of ingots. The model makes it possible to calculate the distribution of hydrodynamic flows in the liquid metal and temperature fields in the ingot, to determine the profile of the metal crystallization front, taking into account the interphase transition zones. The model solves the problem of finding the necessary melting regimes of ingots by calculation, in contrast to high-cost natural experiments. The thermal and hydrodynamic processes during the melting of a cylindrical ingot with a diameter of 110 mm of the newest titanium alloy Ti-6Al-7Nb for medical use were calculated and its melting parameters were determined. The small diameter of the ingot significantly facilitates its further machining. The geometry of the two-phase zone of the liquidus-solidus transition, which determines the crystallization front of the metal, was calculated. The position and geometry of this front greatly affects the quality of ingot formation and the concentration of the distribution of alloying elements and the homogeneity of the metal across its volume. A sufficiently flat crystallization front has been obtained, under which the given conditions are ensured. It was found that heat transfer in the liquid phase of the metal is mainly caused by heat and mass transfer due to its movement, and heat and mass transfer significantly depends on the power of the electron beam and its distribution on the surface of the bath. According to the calculated regimes, at the Institute of Electric Welding named after E. O. Paton, the National Academy of Sciences of Ukraine, high-quality ingots for the needs of the medical industry were smelted. The castings are used for the manufacture of light and ultra-strong endoprostheses and implants, which are chemically neutral and biologically and biomechanically compatible with the human body and do not cause rejection.