通过熔模精密铸造、循环加载和微观组织表征等方法研究了K4169合金循环加载过程中的微观组织演变特征，重点分析了不同循环周次后Laves相和δ-Ni₃Nb相的变形和断裂特征。结果表明，在室温380 MPa应力幅值循环加载实验中，循环寿命主要取决于显微疏松体积分数，裂纹优先萌生于试样表面的显微疏松位置。Laves相的断裂不受循环周次的影响，在循环加载初期，显微疏松附近的长带状Laves脆性相容易开裂，其内部还产生平行排列的二次裂纹，成为裂纹扩展的敏感区域。δ-Ni₃Nb层片呈现2种变形和断裂特征：沿长度方向的开裂；层片表面滑移和断裂。循环加载初期，显微疏松附近的δ-Ni₃Nb层片容易产生沿长度方向的开裂，而随着循环周次的增加，远离显微疏松的δ-Ni₃Nb层片表面滑移迹线逐渐增多直至滑移断裂。γ-Ni基体在循环加载过程中产生孪生变形特征，导致应变局部化程度加剧，进而使Laves相和δ-Ni₃Nb层片周围产生应力集中。

K4169 nickel-based superalloy has been widely used to fabricate high-strength components in aircraft engine. When in service, especially affected by vibration and start-stop process, this alloy is inevitably affected by the external cyclic stress. Therefore, it is of great significance for researchers to understand the microstructure evolution in K4169 while cyclic loading. In the present study, the microstructure evolution of K4169 during cyclic loading has been examined and discussed in detail by using investment casting, cyclic loading and microstructure characterization methods. The cyclic loading test with stress amplitude of 380 MPa was carried out on a pull-push type fatigue machine at room temperature. The dependence of cycle times or fatigue life of specimens with different casting conditions on microporosity content has been discussed. Special emphases have been put on investigating the deformation and fracture characteristics of Laves and δ-Ni₃Nb phases under the influence of microporosity. The results show that the cyclic life was mainly dominated by the content of microporosity. The crack initiation occurred mainly near the microporosity of the specimen surface. The specimen with high microporosity content exhibits the characteristic of complete brittle fracture, while the specimen with low microporosity content exhibits obvious transgranular fracture characteristics. In addition, the fracture of Laves phase was not apparently affected by cycle number. At the beginning of cyclic loading, the long-striped Laves phase near the microporosity was easy to crack, which became the sensitive area of crack growth, and extending in the manner of parallel secondary cracks. The δ-Ni₃Nb plates near microporosity exhibited two obvious cyclic deformation and fracture characteristics depending on their arrangement (or growth orientation) relative to external loading axis: cracking along length direction (or denoted as branch cracking); and exhibiting slip lines and cracks on the surface of δ-Ni₃Nb plates. At the initial stage of cyclic loading, δ-Ni₃Nb plates were prone to crack along the length direction, while the surfaces of the δ-Ni₃Nb plates far from microporosity appear the characteristics of slipping, bending and fracture in turn with the decrease of microporosity content or increase of cyclic cycles. Edge dislocations have been found within δ-Ni₃Nb plates, indicating the transition from screw dislocations to edge dislocations under cyclic loading. Additionally, the twinning deformation of γ-Ni matrix during cyclic loading has been scrutinized through TEM and TKD analyses. The results have been linked to the evolutions of Laves and δ-Ni₃Nb phases, i.e., the evolutions were influenced by the increase of strain localization around Laves and δ-Ni₃Nb phases.