钛合金三次真空自耗电弧熔炼过程中的宏观偏析传递行为

Macrosegregation is a typical solidification defect formed during vacuum arc remelting (VAR) process. This defect adversely affects the property of ingots as the defect sustains even in the subsequent heat treatment process. In the industrial production of titanium alloys, VAR is repeated thrice to eliminate inclusions and improve the homogenization of composition. However, the evolution of macrosegregation during the different stages of the triple VAR process remains unclear. In this study, the melt flow behavior and macrosegregation of titanium ingots in the multistage VAR process are examined via solidification simulations, considering both buoyancy and electromagnetic force. The results show that the strong fluid flow in the upper part of melting pool eliminates nonuniform concentration along the radial direction of the electrode. In contrast, the nonuniform concentration along the axial direction can be inherited in the sequential ingot. However, with the increase in the depth of melt pool, the sustained melt flow from the bottom to upside can reduce the axial macrosegregation delivery. In addition, the use of the previous ingot directly as the electrode for the subsequent remelting process results in severe macrosegregation. However, turning the previous ingot upside-down at least once during the three-stage VAR process can substantially reduce the macrosegregation. Overall, the simulated macrosegregation of Al and V elements in TC4 ingot agree well with that observed in experiment.