A novel directional solidification of tial-based alloys by electromagnetic cold crucible zone melting technology with Y₂O₃ moulds

In order to decrease mould contamination, a novel directional solidification process was developed for TiAl-based alloys, where an Y₂O₃ mould was incorporated into electromagnetic cold crucible (EMCC) zone melting technology. To determine the characteristics of this process, the macro/microstructures and mechanical properties of directionally solidified (DS) Ti45Al2Cr2Nb ingots prepared by two kinds of directional solidification techniques, namely traditional graphite heating (control group) and EMCC heating, were extensively investigated using electromagnetic field and temperature field. Compared with the control group, this new technique can induce bigger electromagnetic force in the tangential direction, generate a more rapid heating and higher temperature gradient, and decrease the interaction between the mould and melt; however the heat transfer is altered to inclining outward owe to the lateral heat transfer. The DS sample prepared by this method can achieve finer columnar crystals growing toward the axis, ¡2/£ lamellae, and lower levels of contamination with regard to Y₂O₃ particles and oxygen. These are beneficial to improve room temperature fracture toughness and tensile properties.