Twinning behavior and strengthening mechanism in a microalloyed TiAl alloy

Abstract

The tensile properties and deformation behavior of a newly developed TNM-based alloy after microalloying with W, C, and Y have been systematically investigated by scanning electron microscopy and transmission electron microscopy. The T435-WCY alloy with a fine and uniform microstructure was obtained by one-step alpha-extrusion processing. Meanwhile, high-density dislocations, deformation twins, and twin intersections were found in the γ lamellae near the tensile fracture. The results showed that compared with the T445 alloy, the addition of trace microalloying elements significantly refined the lamellar colony size and spacing of the T435-WCY. T435-WCY alloy had a good combination of high strength and ductility. The tensile strength and ductility were 964 MPa and 1.60% at room temperature, respectively, and 748 MPa and 9.28% at 850 °C, which was because the grain refinement, high-density deformation twins, and twin intersections were beneficial for improving the strength and plasticity of the TiAl alloy. The dislocation dissociation could promote the formation of deformation twins, and three types of intersecting twins were observed in the γ phase. The twin intersection could hinder the movement of dislocations and relieve stress concentration in the intersection region by lattice distortion, which was beneficial for enhancing the tensile performance of the TiAl alloy.