Additive-manufacturing repair towards restoring fatigue performance of metallic component: experiment and phase-field model prediction

Laser additive manufacturing (LAM) is increasingly employed as an in-situ repair technique for restoring the structural integrity and fatigue performance of metallic components. The fatigue and fracture behavior of LAM repaired components are significantly affected by defects introduced during the repair process, which poses challenges for predicting fatigue properties after LAM repair. Herein, we demonstrate the fatigue strength enhancement and fatigue crack growth (FCG) mechanisms in LAM repaired titanium-alloy blades by integrating vibration-based bending fatigue experiments with phase-field modeling (PFM). It is found that LAM repair of the notched TC17 forged blade could improve the fatigue strength by 94%. Fatigue cracks are revealed to initiate at internal defects within the LAM repair and propagate along transgranular paths influenced by defect clusters, deviating from the surface-initiated cracks in the forged counterparts. X-ray computed tomography reveals that the defect is dominated by small pores, with over 80% exhibiting an equivalent diameter below 60 µm. Furthermore, a macroscopic PFM incorporating fatigue life model that considers repair-induced pore defects is applied to predict the fatigue performance after LAM repair. Phase-field simulation results are shown to agree well with the experimental ones in terms of fatigue strength (error < 6%), critical crack length (error < 8%), and fracture surface morphology. Impact of defect features, material and model parameters on fatigue properties are investigated using our PFM, and the repair-induced pore size is shown to govern fatigue crack initiation and growth behavior of LAM repaired blade. Our work highlights the governing role of LAM repair-induced pore defects in high-cycle fatigue performance and enables a predictive PFM framework applicable to the fatigue evaluation of LAM repaired metallic components.