Effects of Heating Power on Microstructure Evolution and Tensile Properties at Elevated Temperature by Directional Solidification for Ti2AlC/TiAl Composites

To improve the directionally solidified microstructure and tensile properties at elevated temperature, Ti46Al4Nb1C0.8Ta ingots are directional solidified by electromagnetic cold crucible with different heating powers. The microstructure is observed and characterized, tensile properties are tested, and related mechanisms are revealed. Results show that a relatively planar liquid–solid interface is formed under the low heating power (39 kW), which promoted formation of columnar crystals. When the heating power increases from 39 to 48 kW, degree of dent (H1) increases from 8.5 to 18.1 mm and influence length of the initial transition area (H2) increases from 4.3 to 28.6 mm. The formation of a concave liquid–solid interface is due to the high heating power increasing the temperature gradient. High heating power increases the electromagnetic stirring ability, which increases the time to reach stable growth. Tensile properties of the directionally solidified alloy are higher than those of the as-cast alloy under the same testing temperature, e.g., the tensile strength is 342.5 MPa, an increase of 1.4 times, and the tensile strain is 4.4%, an increase of 1.3 times at 950 °C. This shows that the tensile properties and microstructure of TiAl-based composites can be improved by the directional solidification technology.