针对新一代航空发动机涡轮盘用超低C，N含量的变形高温合金GH4065A，系统表征和定量统计了合金的夹杂物组织。对细晶态和粗晶态试样开展了400 ℃和650 ℃不同载荷水平下的疲劳实验。通过对疲劳断裂源组织进行表征分析，研究了合金的疲劳断裂机制。结果表明，合金的夹杂物主要为氮化物。在细晶组织状态下，高温疲劳断裂机制为氮化物（单独和团簇态）起始断裂。高应变幅载荷下（≥0.9%），断裂源主要为试样表面氮化物，极少情况为表面硼化物和氧化物（Al₂O₃和MgSiO₃），且只有Al₂O₃导致合金过早疲劳断裂；低应变幅载荷下（<0.9%），断裂源为氮化物-解理面型，均在试样近表面/内部。两种不同的断裂方式分别导致高应变幅载荷下400 ℃疲劳寿命高于650 ℃疲劳寿命，低应变幅载荷下反之。统计发现，引起疲劳断裂的所有氮化物的尺寸全部达到/超过细晶组织平均晶粒尺寸。在粗晶组织状态下，400 ℃下疲劳断裂机制为准解理起始断裂。晶粒尺寸的增加极大降低了可能诱发疲劳开裂的夹杂物的有效数量，滑移诱发的解理断裂成为主导断裂机制。

GH4065A is a newly developed high-performance cast-wrought Ni-base superalloy with ultra-low C and N content used for advanced turbine engine disc. In this study， the alloy’s inclusions of the alloy are characterized and statistically analyzed. To investigate the fatigue fracture mechanism， strain-controlled fatigue tests are conducted at 400 ℃ and 650 ℃ on the fine-grained and coarse-grained samples respectively. The results show that the alloy’s inclusions of the alloy are mainly nitrides. For the fine-grained samples， discrete nitride particles and clustered nitrides both with a critical size larger than the average grain size are responsible for the fatigue crack initiation. When subjected to high-level strains （≥0.9%）， fatigue failure primarily originates from surface nitrides， with rare occurrences of boride and oxide initiation. Surface crack induced by Al₂O₃， rather than boride or MgSiO₃， is found to significantly reduce the fatigue life. Higher fatigue temperature results in reduced life cycles. When under lower levels of strain， however， subsurface/internal nitride-facet initiations dominate and fatigue life is prolonged by the elevated temperature. In the coarse-grained samples， fatigue failures at 400 ℃ are found to be initiated by quasi-cleavage cracking mechanism. Due to the increased grain size， the inclusion-induced crack initiation is suppressed while slip-induced cleavage cracking mechanism becomes predominant.