Impact toughness and its deformation behavior of a novel low-cost titanium alloy

The burgeoning use of titanium alloys in unmanned underwater vehicles has sparked a surge in demand for low-cost titanium alloys that maintain superior mechanical properties. Despite this, a comprehensive understanding of the deformation mechanisms in low-cost titanium alloys with exceptional impact toughness remains elusive. Therefore, the impact toughness and deformation mechanisms of a novel low-cost Ti-6Al-4V-1.5Mo-1.0Fe alloy with two types of bimodal microstructures (BM1 and BM2) and lamellar microstructures (LM1 and LM2) were studied. The BM2 sample demonstrated an impressive balance of mechanical properties, with a yield strength of 1150 MPa, a tensile strength of 1245 MPa, an elongation of 11%, and an impact energy of 42.59 J. The load‒displacement curves indicated that the energy associated with crack initiation accounted for as much as 85% in the BM samples. By integrating nanoindentation and back stress tests, the deformation behavior near the crack path and the mechanisms of crack initiation were examined. The results revealed that crack initiation was intricately linked to the plastic deformation of the microstructures in the vicinity of the notch tips. The activation of {1 2} < 011> tensile twins in αp, along with the pronounced kink deformation of βt, enhanced the degree of plastic deformation, thereby increasing the crack initiation energy. The proportion of crack propagation energy reached 39% for the LM2 sample. The crack propagation mechanisms were further analyzed via SEM and EBSD. The analysis indicated that the crack propagation energy was synergistically influenced by the deformation in the plastic zone near the crack path and the length of the crack path. The pronounced kink plastic deformation and the convoluted crack path observed in the LM2 sample could alleviate the interface stress concentration, thus improving the energy dissipation during crack propagation.