The α-phase microstructure and texture of a Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy hot-rolled plate can easily lead to anisotropy in impact toughness. This study observed the microstructure and texture of the alloy plate on different planes, conducted impact toughness tests using four combinations of loading direction and crack propagation plane, analyzed the fracture morphology, and investigated the effects of texture and microstructure on the anisotropy of impact toughness. The differences in crack initiation and propagation behavior are discussed. The results show that the impact toughness of the four types of specimens exhibits strong anisotropy. Among them, the L-S specimen (fracture on TD-ND plane, loading along ND) shows the highest impact toughness (97.75 J/cm2), while the T-L specimen (fracture on RD-ND plane, loading along RD) shows the lowest (46.7 J/cm2). Analysis suggests that the strong T-type texture in the plate makes activating slip systems significantly easier for fracture on the TD-ND plane compared to the RD-ND plane. Consequently, the former demonstrates better plastic deformation ability during both crack initiation and propagation. Additionally, the elongated characteristic of α laths along the RD/TD direction and the grain boundary features cause a more tortuous crack path and greater energy consumption when the crack propagates along the ND direction. The combined effect of texture and microstructure determines the anisotropy of impact toughness in this alloy.
Fu et al. (Mon,) studied this question.