镍基单晶铸造气膜孔低周疲劳断裂特征研究

气膜孔结构作为一种重要的热防护技术广泛应用于涡轮叶片中。气膜孔的存在会引入制造缺陷、应力集中等不利因素，成为疲劳失效的主要诱因之一。本研究开展不同温度下镍基单晶铸造气膜孔低周疲劳试验，分析熔模铸造直接成型的气膜孔疲劳断裂特征。结果表明:不同温度下疲劳寿命取决于应力幅值；随温度降低，疲劳断裂路径由Mode-I型转换为晶体学平面断裂，断口形貌呈现出从类解理至韧性断裂特征。气膜孔周围微结构分析表明，在1000 ℃及循环应力作用下，氧化膜发生破裂形成氧化裂纹；在700 ℃条件下，疲劳裂纹形核主要由滑移累积导致；在850 ℃条件下，疲劳损伤由氧化损伤和滑移累积共同作用。晶体塑性有限元分析揭示铸造气膜孔疲劳断裂特征主要受气膜孔附近应力分布的影响。

Study on Low Cycle Fatigue Fracture Characteristics of Ni-based Single Crystal With Casting Film Cooling Hole

The film cooling hole (FCH) structure is widely used in turbine blades as an important thermal protection technology. However, the existence of FCH introduces unfavorable factors such as manufacturing defects and stress concentration, which becomes one of the main causes of fatigue failure. In this study, low cycle fatigue tests in Ni-based single crystal with casting FCH at different temperatures were performed to analyze the fatigue fracture characteristics of FCH, which were directly formed by investment casting. The results show that the fatigue life at different temperatures depends on the stress amplitude. With the decrease of temperature, the fatigue fracture path changes from Mode-I type to crystallographic plane fracture, and the fracture morphology shows the characteristics from quasi-cleavage to ductile fracture. The microstructure analysis around FCH shows that the oxide film breaks and forms oxidation cracks under cyclic stress at 1000 ℃. At 700 ℃, fatigue crack initiation is mainly caused by slip accumulation. At 850 ℃, the fatigue damage is caused by the combined action of oxidative damage and slip accumulation. The finite element analysis of crystal plasticity reveals that the fatigue fracture characteristics of the casting FCH are mainly affected by the stress distribution near the FCH.