Microstructure and elevated temperature tensile property of Ti–46Al–7Nb-(W,Cr,B) alloy compared with binary and ternary TiAl alloy

The newly developed high-Nb TiAl with a small amount of W, Cr, and B addition prepared by electromagnetic cold crucible has been investigated by comparing with the microstructure and elevated temperature tensile properties of binary and ternary high-Nb TiAl alloy. Results indicate that microstructures of the three alloys are fully lamellar (FL), near fully lamellar (NFL) and near fully lamellar alloy with TiB (NFL + TiB). The dispersed TiB particles in the alloy have the B27 structure and are highly enriched with Nb and W but depleted with Al by the characterization of transmission electron microscopy. The elevated temperature tensile test results show that the high-Nb TiAl alloy with NFL + TiB microstructure exhibits excellent mechanical properties compared with the other two alloys, and the tensile strength and elongation at 800 °C are 648 MPa and 5.73%, respectively. Fracture morphology shows the alloy has a mixed mode of trans-lamellar and inter-lamellar fracture. As the dispersed second phase particles, rod-like TiB can act as the obstacle to crack propagation and dislocation movement. The excellent mechanical properties of the alloy at elevated temperatures are attributed to the combined effects of dislocation block and nanotwins formation during deformation within the γ lamellae. Moreover, the probable generation and propagation mechanism of dislocations and twins in the γ lamellae are further discussed.