Low-temperature impact toughness and deformation mechanism of CT20 titanium alloy

The impact toughness and deformation mechanism of near-alpha-type low-temperature titanium alloy CT20 at different temperatures (20 degrees C, 0 degrees C,-50 degrees C,-100 degrees C and -196 degrees C) are studied. The results show that the impact toughness is as high as 90 J/cm2 at 20 degrees C, and does not decrease obviously at 0 degrees C,-50 degrees C and -100 degrees C, but brittle fracture occurs at-196 degrees C (29 J/cm2). The tortuosity of the crack path decreases with decreasing tem-perature. At 20 degrees C, the grain boundary and alpha colony interface with high-angle grain boundary deflect the crack propagation direction effectively, forming a tortuous crack path, while crack tends to cut through alpha lamellae, forming a relatively straight path at cryogenic temperature. The lamellar alpha undergoes kink deformation at 20 degrees C, showing severe plastic deformation characteristics. In addition, deformation twins and geometrically necessary dislocations (GNDs) are observed near and far from the fracture surface, indicating that the plastic zone is large. As the temperature decreases, the twin density near the crack path tends to increase. However, few twins are seen in the region far from the fracture surface, and GND densities are low at-196 degrees C, implying that the plastic zone is small. In a word, the synergistic effect of tortuous crack path, dislocation slip and deformation twinning enable CT20 to achieve high impact toughness at 20 degrees C. At-196 degrees C, the plastic deformation capacity of the microstructure decreased significantly, resulting in the formation of a small plastic zone and brittle fracture.