Abstract This study investigates the fatigue behavior of Inconel 718 (IN718) fabricated through laser beam directed energy deposition (LB-DED) process. Fully-reversed (Re = −1) strain-controlled fatigue tests are conducted on LB-DED IN718 specimens at 650 °C and the results are compared with those of LB-DED IN718 specimens tested at room temperature as well as the ones obtained from wrought counterparts at both room temperature and 650 °C. The microstructure is characterized after fabrication, heat treatment, and fatigue tests at elevated temperature. Microstructure characterizations reveal that as-built LB-DED IN718 has a dendritic structure. The heat treatment applied could not eliminate the dendritic structure, and needle-like δ phases are formed on the grain boundaries. The comparison of LB-DED and wrought fatigue results show that the LB-DED IN718 possesses slightly lower fatigue resistance at room temperature, while exhibits a comparable fatigue strength at elevated temperature. In the low cycle regime, the fatigue resistance of LB-DED IN718 tested at elevated temperature is somewhat inferior to the ones tested at room temperature, which can be explained by the formation and growth of brittle needle-like δ and Laves phases on the grain boundaries during fatigue testing at elevated temperature and their effects on increasing the fatigue crack growth rate. In the high cycle regime, however, LB-DED IN718 specimens tested at elevated temperature had somewhat similar fatigue lives to the ones tested at room temperature. This may be partially explained by the surface oxidation during fatigue testing at elevated temperature, which can retard the microstructurally short cracks to grow.

中文翻译：

---

高温循环载荷下增材制造 Inconel 718 的疲劳行为和微观结构演变

摘要 本研究调查了通过激光束定向能量沉积 (LB-DED) 工艺制造的 Inconel 718 (IN718) 的疲劳行为。在 650 °C 下对 LB-DED IN718 试样进行完全反向（Re = -1）应变控制疲劳试验，并将结果与​​室温下试验的 LB-DED IN718 试样以及从在室温和 650 °C 下锻造对应物。在制造、热处理和高温疲劳试验后表征微观结构。微观结构表征表明，竣工的 LB-DED IN718 具有树枝状结构。热处理不能消除枝晶组织，在晶界形成针状δ相。LB-DED 和锻造疲劳结果的比较表明，LB-DED IN718 在室温下具有稍低的疲劳强度，而在高温下表现出相当的疲劳强度。在低循环状态下，LB-DED IN718 在高温下的抗疲劳性略逊于室温下的测试，这可以通过晶粒上脆性针状 δ 和 Laves 相的形成和生长来解释高温疲劳试验过程中的边界及其对增加疲劳裂纹扩展速率的影响。然而，在高循环状态下，在高温下测试的 LB-DED IN718 试样的疲劳寿命与在室温下测试的试样有些相似。