An examination of the factors influencing the melting of solid titanium in liquid titanium

The melting behavior of a solid in liquid titanium has been investigated with the aid of an Electron Beam Button Furnace (EBBF) to understand the phenomena contributing to the melting of exogenous solids introduced into liquid titanium during melt processing and casting. In this work, cylindrical rods of commercial purity (CP) titanium were dipped into a molten CP titanium pool for various periods of time to investigate the melting behavior in the absence of compositional effects. The dimensions of the dipped rods were measured before and after various immersion times allowing for quantification of the evolution of the solid/liquid interface and melting rate. The temperature within the dipped rod was also monitored during immersion to provide additional quantitative data on heat transport for analysis. The results show that the liquid titanium initially freezes onto the cold rod sample when it was immersed, resulting in the formation of a solid/solid interface between the immersed rod and the frozen titanium. It was found that the solid/solid interface exerts a significant resistance for heat transfer. After a short period of time, the frozen titanium melted followed by melting of the rod. A numerical model has been developed to describe the experimental process, the results of which are shown to correlate well with the experimental observations and measurements. Analysis with the model has confirmed that thermally induced buoyancy and, in particular, thermally induced Marangoni forces have a considerable impact on the transport of heat and momentum, and consequently on the melting kinetics. For the convenience of use in practical industrial-scale applications, effective interfacial heat transfer coefficients (EIHTCs) have been calculated based on the numerical model results. In addition, EIHTCs were also solved from the similarity solution after simplifying the problem description, showing that they can correlate satisfactorily if an appropriate reference temperature is selected.