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

Abstract

This study systematically investigated the influence of multi-directional forging (MDF) on the microstructural evolution, hot deformation behavior, and tensile properties of a β-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 °C and a forging speed of 0.1 mm/s, indicating that MDF can be applied to β-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 γ grains and a small amount of β 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 (δ) at room temperature were 689.4 MPa, and 0.83%, respectively. The alloy exhibits excellent ductility at 700 °C. When the temperature was increased to 700 °C, the UTS decreased to 556 MPa and δ increased to 5.98%, indicating that the alloy exhibits excellent ductility at 700 °C. As the temperature further increased to 750 °C, δ dramatically increased to 46.65%, indicating that the ductile-brittle transition temperature of the alloy is between 700 °C and 750 °C.

The Microstructural Evolution, Tensile Properties, and Phase Hardness of a TiAl Alloy with a High Content of the β Phase

“…Thermal deformation is a suitable way to obtain a fine-grained microstructure, which is beneficial for the ductility of TiAl alloys [5,8]. Past research has confirmed that the hot workability of TiAl alloys can be significantly enhanced by the β phase with a disordered body-center cubic lattice at above 1150 °C [9,10]. The content of the β phase depends closely on β-stabilizers.…”

Hot Deformation Behavior and Microstructural Evolution of a Novel β-Solidifying Ti–43Al–3Mn–2Nb–0.1Y Alloy

“…This indicates that the ductile–brittle transition temperature (DBTT) of the current alloy should be 750–800 °C. According to previous studies, the DBTT of TiAl alloys without Nb is just 700–750 °C [20]. By contrast, the DBTT of high-Nb containing TiAl alloys can reach to more than 800 °C due to the high Nb content [46].…”

“…The microstructure of the as-forged billet was analyzed by electron back-scattered diffraction (EBSD, FEI, Hillsboro, OR, USA). Samples for TEM and EBSD were prepared using a standard procedure, which has been described in previous research [20].…”