Intrinsic control mechanism of tensile and impact toughness of TC21 titanium alloy

Abstract:

TC21 alloy has high strength and fracture toughness, however, the mechanism of crack initiation and propagation during impact is not clear, and the relationship between impact toughness and tensile properties is yet to be studied. In this work, different microstructures are prepared by regulating the solid solution temperature and cooling rate to study the tensile and impact properties. The results show that tensile performance and impact toughness exhibit different variation laws. The impact toughness of the bimodal structure with better plasticity is lower than that of the full lamellar structure with the worst plasticity, indicating that the intrinsic control mechanisms of tensile properties and impact toughness are different, which is further confirmed by the post-aging properties (no significant change in plasticity but significant decrease in impact toughness after aging). During tensile deformation, plastic deformation occurs in the whole region of the specimen before necking occurs, and the coordination deformation between α_p and β_t in the bimodal structure is fully developed, while the full lamellar structure has a larger colony size and its internal lamellar α orientation is uniform, and the dislocation slip length is larger, making it susceptible to plastic strain localization, resulting in a poorer strength plasticity matching than that of the bimodal structure. Under the influence of high strain rate, the crack initiation and propagation at the notch root are rapid, and the plastic deformation is concentrated in a small range near the crack tip, resulting in the coordination deformation between α_p and β_t cannot be fully played. In this case, the colony interface of the full lamellar structure has little influence on the plastic deformation, and the lamellar α and β become the control units of plastic deformation. The coarse lamellar α/β has better plastic deformation ability, resulting in higher crack initiation energy, contrary to the poor plasticity exhibited by stretching. In addition, the large angle interface of α colony causes the deflection of cracks and forms a tortuous path, resulting in higher impact toughness than the bimodal structure.