Dissolution Rate of Nitrided Titanium Sponge in Liquid Ti–6Al–4V and Fate in Plasma Arc Melting Process

Abstract Inclusion cleanliness in titanium alloys is an essential and mandatory requirement for the safe operation of aerospace components. During the production and processing of titanium alloys, inclusions may form—especially so-called low-density inclusions (LDIs), which often consist of unintentionally nitrided titanium sponge. Plasma arc melting with cold hearth refining (PAMCHR) is one of the most efficient recycling and refining processes for titanium alloys, which must guarantee the elimination of any LDIs initially present in the feedstock. A full 3D thermo-hydrodynamic model of the PAMCHR process has been previously developed. We additionally propose a Lagrangian approach to compute particle trajectories, coupled with the dissolution model, in order to describe the behavior of LDIs within the process. An experimental study combined with mathematical modeling has been conducted to propose a dissolution kinetics of these particles in a Ti–6Al–4V (Ti64) alloy bath, taking into account their morphology and surface condition as porous particles. The whole numerical model is then applied to a 100 kg/h Ti64 melting test performed in a pilot-scale furnace. Statistics over a large number of simulated LDIs provide probabilistic estimates of the proportion of eliminated particles, either by trapping or dissolution, and of those that remain.