Effects Of DC Current On Directional Solidification Process Of Tial-based Alloy

Because of the high specific strength, high specific stiffness, and good high temperature oxidation resistance, creep and hydrogen embrittlement resistance and other characteristics, TiAl-based alloy has been an excellent lightweight heat-resistant material in improving the efficiency of the engine and has been considered the next generation of new engine materials. However, low plasticity at room temperature limits its promotion and application. Controlling the casting solidification process of materials is an important way to improve the performance of castings and develop new materials. In recent years, there have been many new solidification technologies which are introduced by adding an external field to influence the solidification process, so as to enhance the material properties. Wherein the current study, the technique of electric current-solidification has been a hot research direction, but most of the research is to examine the low melting point alloy under the effect of electric current without considering the high melting point alloy. The effect of electric current on the directional solidification process and microstructure of TiAl-based alloy is the topic of this paper.Numerical simulation method has been used to study the distribution of magnetic induction intensity in alloy with different turns of induction heating coil and size of current, the results can verify the correctness of directional solidification experiments and improve experimental process parameters for Ti-48Al-2Cr-2Nb alloy which is prepared by directional solidification under the effect of electric current. The study shows that the distribution of magnetic induction intensity in alloy doesn’t changed with the increasing of induction heating output current, however the reduction of the turns can improve the distribution of the magnetic induction at the solid-liquid interface of the alloy significantly.In order to observe the solidification process under the effect of electric current clearly, physical simulation approach was used. By analyzing the behavior of hypoperitectic mimetic AMPD-4.1at%SCN in the directional solidification process, we find that as the current density increasing, the primary dendrite arm spacing of peritectic β phase decreases linearly.This article design the experimental facility which can work under the action of electric current, and using Ti-48Al-2Cr-2Nb do the experiment of directional solidification under different electric current, then get the casting of directional solidification.. Optical microscopy and scanning electron microscopy were used for microstructure observation. The study shows that as the current density increasing, the interface between the initial solidification zone and stable growth zone will change from convex shape to a smooth line. During the growth of directional solidification process the change makes the interface form an evenly heated one. When loading current density is in the range of0-60.6mA/mm2, the formation of columnar grain is inhibited and the formation of equiaxed grain is promoted. When the loading current density increases to90.9mA/mm2, the current will promote the formation of columnar grain and refine columnar crystals during the directional solidification process of the Ti-48Al-2Cr-2Nb alloy.