Effect Of Convection On The Directional Solidification Of Ti-45Al Peritectic Alloy

It is very important to study the process of peritectic reaction in the directional solidification since it was involved in solidification of many structural materials and functional materials. In this paper, the directional solidified samples of Ti-45A1 hypoperitectic were prepared using electromagnetic induction heating and liquid metal cooling technique. The structures obtained at different withdrawing velocities and different convection were observed and analyzed by optical microscopy and SEM.. The influence of convection on the solidification structures was also analysed.Firstly, a set of system which can supress fluid flow was designed and machined according to running liquid metal can form an oppsite directional applied force in steady magnetic field. Experiment on imposition static magnetic field was performed by Al-Cu alloy and found that temperature is invariable, which indicated the steady magnetic field can supress convection of liquid metal at solid/liquid interface.Secondly, quenched interface morphologies are planar interface, cellular interface and dendrite interface repectively, when drawing velocity is 5μm/s, 10μm/s and 50 μm/s. The angel between the lamellar boundaries(α₂-Ti₃Al/γ-TiAl) and growth direction is 90° , 45° or 0° , which indicate the primary phase can be stable phase β or metastable phase a. And with the increase of drawing rates ,volume fraction of perpendicular lamellar with the growth direction increase. However, when drawing rate is 50μm/s, The angel the lamellar boundaries and growth direction is 45° or 0°, it shows that the primary phase is stable phase β.Finally, microstructure evolution and phase selection were studied at different convection by using imposition steady magnetic field and altering thickness of graphite shell to decrease magnetic flux density in the induction coil. The experiment can achieve parallel columnar crystals with growth direction by decreasing electromagnetic stir force and supressing convection. The stable phase β is primary phase and lamellar boundaries(α₂/γ) is parallel or 45° with growth direction. Lamellar space increase with convection decrease. After the imposition of the steady magnetic field, convection was supressed during the directional solidification. Quenched interface morphology showed dendritic crystals grow at the same speed . The irregular banded structure was observed under the condition of the imposition of the static magnetic field, which indicate that...