Effect of Multi-Directional Forging on the Microstructure and Mechanical Properties of -Solidifying TiAl Alloy

This study systematically investigated the influence of multi-directional forging (MDF) on the microstructural evolution, hot deformation behavior, and tensile properties of a -solidifying TiAl alloy. The initial lamellar microstructure of an as-cast alloy was remarkably refined and homogenized by three-step MDF. High temperatures and multi-pass deformations were conducive to the decomposition of lamellae. A crack-free billet was obtained through three-step MDF, with a deformation temperature of 1250 degrees C and a forging speed of 0.1 mm/s, indicating that MDF can be applied to -solidifying TiAl alloys by the proper control of the alloy composition and process parameters. Microstructural observation showed that the billet mainly consists of fine and equiaxed grains and a small amount of phase. The tensile properties of the multi-directional forged alloy were also significantly improved, due to microstructure refinement. The ultimate tensile strength (UTS) and elongation () at room temperature were 689.4 MPa, and 0.83%, respectively. The alloy exhibits excellent ductility at 700 degrees C. When the temperature was increased to 700 degrees C, the UTS decreased to 556 MPa and increased to 5.98%, indicating that the alloy exhibits excellent ductility at 700 degrees C. As the temperature further increased to 750 degrees C, dramatically increased to 46.65%, indicating that the ductile-brittle transition temperature of the alloy is between 700 degrees C and 750 degrees C.