In Situ Transmission Electron Microscopy Study of Titanium–Steel Heterostructure: Real‐Time Analysis of Interfacial Fracture Evolution

Titanium (Ti)–steel composite joints are prone to the formation of compounds such as TiC, TiFe, and TiFe 2 during solid‐phase bonding. This phenomenon leads to premature failure and significantly reduces the bonding quality of the joints. However, the fracture behavior of the joint influenced by these compounds, particularly on the initiation of cracks, is yet to be elucidated. Therefore, a comprehensive investigation of the fracture behavior of Ti–steel joints is essential for understanding interfacial failure mechanisms. This paper presents the fabrication of a joint between pure titanium TA2 and 45 steel, prepared through solid‐phase diffusion bonding. The original morphology of the bonding interface was characterized using scanning electron microscopy and transmission electron microscopy. Subsequently, the tensile fracture behavior of the interface was observed in real‐time using an in situ tensile stage within the TEM. The results indicate that a continuous TiC reaction layer formed at the interface during bonding, with the phase composition on either side of the interface being α‐Fe and TiC at the microscopic scale. In situ tensile results revealed that cracks were found to initiate not at the α‐Fe/TiC interface, but approximately 200 nm from the interface on the steel side. This is attributed to the strain localization in the steel region caused by inconsistent deformation between the two phases. This finding provides theoretical guidance for microstructural design and quality optimization of Ti–steel heterostructures.