Mechanical‒Thermal coupled fatigue behavior and failure mechanisms of additively manufactured Ti6Al4V alloy

Despite the widespread adoption of Ti6Al4V in aerospace applications, driven by its balanced performance at elevated temperatures (up to 600 °C) combined with cost-effectiveness, our understanding of its fatigue behavior under real-world operating conditions-particularly in elevated-temperature mechanical-thermal coupling environments—remains limited. For example, turbofan blades experience concurrent centrifugal tensile loads and thermally-induced bending stresses from aerodynamic and combustion environments, and the precise deformation mechanisms causing fatigue failure under tensile-bending loads and thermal coupling are not fully understood, which limits further improvements in reliability and fatigue performance. In this study, Ti6Al4V samples were fabricated via the laser powder bed fusion (L‒PBF) technique at different scanning speeds for mechanical‒thermal coupling fatigue tests under combined tensile‒flexural loading in the temperature range from room temperature to 600 °C. The experimental results reveal an exponential decrease in the fatigue life as the temperature increases. Fracture morphology analysis indicates that higher temperatures promote significant plastic deformation and the formation of secondary microcracks, both of which accelerate the fatigue failure process. Microstructural examination using electron backscatter diffraction (EBSD) revealed a decrease in grain size and a change in the grain orientation, suggesting a shift in the plastic deformation mechanism. These findings highlight the role of dislocation mobility and grain refinement in accelerating crack propagation and shortening the fatigue life at elevated temperatures.