Y ves Nadot

A Laser Powder Bed Fusion Inconel 718 produced with intentionally non optimized parameters is investigated to elucidate the role of defects and microstructure on the High Cycle Fatigue life. Samples coming from three build orientations and three heat treatments are tested at room temperature and at 650 °C under R = 0.1 load ratio. Results show that the printing orientation has a minor effect on fatigue life at both room and high temperatures. Most samples failed from Lack of Fusion type defects (ranging from 200 µm to 600 µm) and each defect size is carefully analyzed by using SEM observations. It can be observed that surface defect leads to transgranular fracture surface when sub-surface initiation leads to rather crystallographic type fracture surface. By producing S-N curve on Hot Isostatic Pressure condition, it is shown that the relative influence of defect on the S-N curve is much higher at 20°C compared to 650°C. Kitagawa diagram are plotted for both temperatures in order to quantify the influence of defect size on the fatigue limit. Natural cracks are observed at the surface in order to discuss the relative part of initiation life in the whole fatigue life.