Fracture behavior and mechanism of diffusion-bonded Ti-6Al-4V titanium alloy under thermal deformation

Understanding the high-temperature fracture behavior of diffusion-bonded Ti-6Al-4V is essential for process optimization and improving service performance. This study systematically investigates the fracture behavior of diffusion-bonded Ti-6Al-4V under thermal deformation, and a fracture behavior transition from brittle fractures at low temperature and high strain rate (e.g. 1023 K, 0.1 s⁻¹) to ductile fractures at high temperature and low strain rate (e.g. 1123 K, 0.01 s⁻¹) has been characterized and analyzed. Microstructural mechanisms are investigated using optical microscopy (OM), scanning electron microscopy (SEM), X-Ray Diffraction (XRD) and electron backscatter diffraction (EBSD). Brittle fractures are attributed to the presence of straight grain boundaries (SGBs) and weak joints formed during the diffusion bonding process, which facilitated rapid void nucleation and coalescence along the bonding interface. In contrast, ductile fractures are driven by larger equilibrium subgrain sizes (λ) and enhanced grain boundary sliding (GBS) at higher temperatures and lower strain rates. This combination reduces dislocation pile-up, eliminates SGBs, and promotes continuous dynamic recrystallization (CDRX) within larger grains, thereby coordinating deformation and mitigating crystallographic mismatch, ultimately leading to ductile fracture.