Room-temperature tensile deformation of polysynthetically twinned (PST) crystals of TiAl

Abstract

Tensile deformation behavior of polysynthetically twinned (PST) crystals of TiAl with a nearly stoichiometric composition was investigated as a function of the angle ø between the lamellar boundaries and tensile axis at room temperature. Tensile elongation to fracture strongly depends on the angle ø but its dependence on the angle ø is not symmetrical with respect to ø = 45°. A tensile elongation as large as 20%, which is far larger than any other reported values on TiAl-based compounds, has been obtained for ø = 31°. The yield stress also strongly depends on the angle ø but any particularly significant tension-compression asymmetry in yield stress has not been observed. Fracture has been found to occur in a brittle manner without showing any local contraction even after deformation to more than 10%. When the tensile axis is perpendicular or inclined to the lamellar boundaries, fracture occurs in a cleavage-like mode with a habit plane parallel to the lamellar boundaries while fracture occurs in a zigzag across the lamellar boundaries when the tensile axis is parallel to the lamellar boundaries.