Numerical Investigation on the Evolution Behavior of Solidification Structure in Titanium Alloy During Vacuum Arc Remelting Process

High-temperature titanium alloys, with the advantages such as low density, high specific strength, and excellent high-temperature creep resistance, are critical structural materials for achieving weight reduction and improving thrust-to-weight ratio in aerospace engines. The primary method for industrial production of titanium alloy ingots is Vacuum Arc Remelting (VAR) technology. However, large-sized titanium alloy VAR ingots are prone to metallurgical defects such as compositional segregation, uneven solidification structure, and inclusions, which are closely related to the evolution behavior of solidification structure during the remelting process. The evolution patterns and formation mechanisms of the solidification structure in titanium alloy are not yet clearly understood. The heat transfer phenomena and solidification structure distribution during the VAR process of large-sized titanium alloy ingots were investigated using the cellular automaton-finite element (CAFÉ) model. The inherent mechanisms governing grain nucleation and dendritic growth processes were explored, and the influence of typical process parameters on the solidification structure was analyzed. The results indicate that the solidification structure near the surface of the ingot is primarily columnar in shape. As the temperature gradient decreases and the solidification rate increases, a transition from columnar to equiaxed grains occurs, with the corresponding range of temperature gradient between 2.2 and 2.6 K/mm, solidification rate ranging from 0.04 to 0.046 mm/s, and mapping factor ranging from 50 to 70. Increasing the current intensity primarily suppresses grain nucleation and promotes the growth of columnar grains by affecting the solidification rate and mapping factor near the sidewall of ingot.