【摘要】 为了研究O累积程度对晶界损伤的影响规律及其表征方法，本工作设计了一系列不同参数的时效实验以导入不同O累积程度变量。对时效后的GH4738镍基高温合金试样进行室温疲劳裂纹扩展实验，通过疲劳断口由穿晶模式完全转变为沿晶模式所对应的应力强度因子范围(ΔK)，对合金O累积导致的晶界损伤进行评估，通过分子动力学理论计算并验证实验得到的沿晶断裂模式转折点的变化规律。实验研究和理论计算结果表明，随着O累积程度增加，疲劳裂纹扩展速率增加，疲劳寿命降低，疲劳断口的完全沿晶模式转折点更靠近起裂端。O元素引起晶界分离功降低，随着O原子浓度升高，晶界弱化现象更为显著。此外，温度越高，晶界分离功下降速率越快。更多还原

【Abstract】 Fatigue is an important failure mode arising during the service conditions of superalloys. The fatigue crack propagation behavior of superalloys is influenced by many factors, such as temperature, stress, and ambient O. Among these, ambient O plays an important role. Numerous studies showed that fatigue crack propagation in a vacuum proceeds mainly as a transgranular fracture, while in air, it occurs mainly as an intergranular fracture. This is because the grain boundary is oxidized, making it weak. There is a lack of studies on the influence of different degrees of O accumulation on oxygen-induced grain boundary damage and ways to characterize this influence. The degree of O accumulation at the grain boundary is usually difficult to evaluate quantitatively. Therefore, to investigate the influence of O accumulation on the damage to grain boundary and to devise a method to characterize this influence, this study designed a series of aging experiments with different parameters to introduce different O accumulation variables. The fatigue crack growth test of aged nickel-based superalloy GH4738 was performed at room temperature((23 ± 3) ℃). For higher aging temperatures and longer aging time, the fatigue crack growth rate was higher, and the fatigue life was shorter. The fatigue fracture morphologies were observed. The grain boundary damage caused by the O accumulation was evaluated by considering the stress intensity factor range(ΔK), corresponding to the complete transformation of fatigue fracture from the transgranular mode to the intergranular mode. The grain boundary separation work calculated based on the molecular dynamics theory was used to verify the law of change in the turning point of the intergranular fracture mode observed experimentally. The experimental and theoretical results taken together showed that with an increase in O accumulation, the fatigue crack growth rate increases, service life decreases, and the turning point of the complete intergranular mode of fatigue fracture approaches the crack initiation end. O caused a reduction in the grain boundary separation work. As the O atom concentration increased, the weakening of the grain boundary became more pronounced. Addition, the higher temperature resulted in faster reduction rate of the grain boundary separation work.更多还原