In-situ SEM investigation and modeling of small crack growth behavior of additively manufactured titanium alloy

The fatigue crack growth of wire and arc additive manufactured Ti-6Al-4V alloys is investigated using in-situ SEM fatigue testing. The small crack initiation and propagation behaviors within grains and across grains are systematically studied, and the inter- and trans-granular crack growth rates are quantified. A synergy and competition among many factors such as persistent slip bands, grain boundaries, and crack branching governs the growth rate. A modified model based on the CTOD is proposed to characterize the growth rate considering the microstructure dissimilitude and local yield strength variations. Results show the proposed model improves the prediction accuracy.