Abstract
Segregation defects greatly affect the service performance and working life of castings during the vacuum arc remelting (VAR) process. However, the corresponding research on the prediction of segregation defects is still not comprehensive. Through considering the influence of water-cooled crucible on the electromagnetic field inside an ingot, a full-scale model for the comprehensive prediction of freckles and macrosegregation defects during the VAR process is developed in this paper. The macroscopic solute transport phenomenon and the segregation behavior of Ni-5.8 wt% Al-15.2 wt% Ta alloy are predicted. The results indicate that the freckles are mainly concentrated in the lower region of the ingot. With the growth of the ingot, the solute enrichment channels gradually develop into solute enrichment regions, and the channel segregation evolves into macrosegregation. The Lorentz force mainly affects the flow pattern at the top of the molten pool, while the complex flow of multiple vortices is dominated by thermosolutal buoyancy. The maximum and minimum relative segregation ratio inside the ingot can reach 290% and −90%, respectively, and the positive segregation region accounts for about 79% of the total volume. This paper provides a new perspective for understanding the segregation behavior inside the ingot by studying the segregation evolution during the VAR process.
Highlights
Ni-based superalloys have been widely used to manufacture key hot-end components of aeroengines and large gas turbines due to their high creep resistance and fatigue strength, good oxidation, and hot corrosion resistance at high temperatures [1]
The difference of boundary conditions mainly affects the distribution of magnetic induction intensity, and changes the distribution of the Lorentz force, and will affect the predicted flow pattern in the molten pool and segregation behavior of the ingot
This is mainly due to the fact that before the consumable electrode is completely melted, the depth of the molten pool gradually decreases with the increase in ingot height, and the convection in the upper part of the molten pool is dominated by the transverse flow caused by the combined action of thermosolutal buoyancy and Lorentz force, as shown in Figures 9a and 10a
Summary
Ni-based superalloys have been widely used to manufacture key hot-end components of aeroengines and large gas turbines due to their high creep resistance and fatigue strength, good oxidation, and hot corrosion resistance at high temperatures [1]. It can be found that due to the symmetry of molten pool, flow pattern, and electromagnetic field distribution, two-dimensional axisymmetric or three-dimensional non-full-scale models are mostly used in related research. These works have great potential to help one understand the basic physical phenomena in the Metals 2021, 11, 2046. In order to fully explore the segregation behavior inside the ingot during the VAR process, a three-dimensional full-scale model for comprehensive prediction of freckles and macrosegregation defects was developed in this paper, and the influence of crucible on the electromagnetic field distribution inside the ingot was considered. It is expected to play a guiding role in actual production
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