Proactively introducing defects and forming twinning and low angle grain boundaries in the γ phase to particularly improve the 900 °C tensile strengths of theTi-47Al-6Nb-0.1C-1.6Ta alloy

Actively introducing different types of defects into γ phase with lower formation energy is an effective method to improve the mechanical properties of TiAl alloys at room and high temperatures. Ta was added in Ti-47Al-6Nb-0.1C alloy (TiAl-0Ta alloy), and defect types, microstructure, mechanical properties at room and 900 °C, and related mechanisms were studied. Results show that four kinds of surface defects are formed in the γ phase between lamellar colonies after adding Ta, including stacking faults (SFs), twin boundaries (TB), low angle grain boundaries (LAGB) and 120° rotation boundaries (RB). Ta promotes SFs generating by reducing the stacking fault energy. Insertion of extrinsic SF changes the stacking order to generate twin. The continuous generation of SFs leads to the widening of twins. Ta substitute Al will form lattice distortion and vacancies. Vacancies are filled by Al atoms to form edge dislocations, resulting in LAGB. The substitution also reduces the formation energy of the RB to form that. Compressive strength and strain of Ti-47Al-6Nb-0.1C-1.6Ta alloy (TiAl-1.6Ta alloy) reached 2606 MPa and 40.6 %, and the 900 °C tensile strength and elongation of alloy reached 550.2 MPa and 10.8 %. The edge dislocation at LAGB, elastic stress field at TB and RB increase the critical resolved shear stress of dislocation and hinder dislocation slip. The SFs decompose the dislocation into partial dislocations to consume its energy.