Effect of internal stresses on the fracture toughness of a TiAl-based alloy with duplex microstructures

Abstract

A series of fine duplex microstructures with different volume ratios of equiaxed γ and lath colonies (α 2+γ) were achieved from an isothermally forged Ti–46.5Al–2Cr–2Nb alloy. The internal stress determination using X-ray diffraction techniques and plane-strain fracture toughness tests were carried out at room temperature, and the effects of the internal stresses on the fracture toughness were investigated. It was found that the internal stresses play an important role in determining the fracture toughness of the TiAl-based alloy. The compressive internal stresses in γ phase and the tensile internal stresses in α 2 phase may be responsible for the delamination along the γ/α 2 boundaries. For the microstructures with different volume fraction of lamellar grains, the fracture toughness increases with the internal stresses, which facilitate the formation of shear ligaments; and the effects of the α 2 phase and equiaxed gamma grains on the internal stresses and the fracture toughness were discussed.