Effect of foreign object damage on fatigue performance of Inconel 718 welded joints

Foreign object damage (FOD) in Inconel 718 base metal(BM) and welded joints(WJ) was investigated using pendulum impact testing. The effects of impact energy on damage morphology, microstructure, and fatigue performance were analyzed. The results show that: 1. The fatigue life and hardness inherent in WJ are higher than those of the BM, primarily due to grain refinement and the presence of precipitated phases at grain boundaries; 2. Macroscopically, the damage notches exhibit a V-shape. Their dimensions increase with the rise in impact energy. However, under the same energy level, the damage dimensions of WJ are smaller than those of the BM; 3. Microscopically, the damage of the BM mainly manifests as crack initiation at the carbide interfaces. In contrast, a large number of holes and microcracks form at the precipitated phases in WJ; 4. Under low-energy impact, WJ possess a higher fatigue life than the BM. This is attributed to their smaller damage dimensions and finer grain structure. Nevertheless, under high-energy impact, the numerous voids and cracks generated inside WJ lead to a sharp decline in their fatigue life, which even become lower than that of the BM.