The effect of standard heat treatments and process conditions on the fatigue performance of wire arc additively manufactured Ti-6Al-4V

Wire arc additive manufacturing (WAAM) offers a cost-effective route for producing large, customised Ti-6Al-4V airframe components, yet the influence of heat treatments and process conditions on fatigue life remains unclear. This study examines how fatigue performance is shaped by standard additive manufacturing heat treatments (SR, STA, HIP, annealing) and key process parameters, including nozzle to workpiece distance and shielding atmosphere. STA refined the microstructure and increased strength but produced little improvement in fatigue life, while SR had negligible effects due to already low residual stresses in the as-machined state. In contrast, annealed specimens built with a more optimal nozzle to workpiece distance showed improved fatigue life despite lower yield strength, driven by high relative density (>99.99 percent) and greater ductility. HIP produced full densification and the best fatigue performance. Poor shielding reduced relative density and degraded fatigue resistance, despite strengthening from diffused oxygen. Fractography revealed that fatigue cracks initiated at sharp notches around clustered gas pores, where high stress concentrations accelerated crack coalescence and ligament rupture. Overall, the results demonstrate that clustered porosity, not microstructural refinement or strength alone, governs fatigue life in WAAM Ti-6Al-4V, highlighting the need to control pore nucleation and growth for reliable aerospace use.