The detrimental effects of carbides and porosity on the fatigue crack initiation and propagation of nickel-based single-crystal superalloys have been reported by many previous studies. However, few studies have quantitatively compared the fatigue damaging effects of carbides and pores on the fatigue crack evolution. In this study, a high-resolution X-ray computed tomography (XCT) characterization of a DD5 nickel-based single-crystal superalloy during fatigue test was performed. The evolution of carbides, pores and cracks at all stages was observed and tracked. In order to quantify the 3D microstructures, a new damage factor that correlates the morphology of fracture surface with crack evolution behaviors was proposed. It was found that porosity was more detrimental than carbides in crack initiation and propagation during fatigue tests. Furthermore, pore spacing has been found to be the most significant factor among all controlling pore characteristics in the crack initiation stage and sphericity is the most critical pore characteristic in the crack propagation stage. Therefore, by statistically analyzing the evolution of carbides and pores during fatigue tests in this study, the underlying fatigue cracking mechanism of nickel-based superalloys is revealed.

许多先前的研究已经报道了碳化物和孔隙率对镍基单晶高温合金疲劳裂纹萌生和扩展的不利影响。然而，很少有研究定量比较碳化物和气孔对疲劳裂纹演变的疲劳破坏作用。在这项研究中，对 DD5 镍基单晶高温合金在疲劳试验期间进行了高分辨率 X 射线计算机断层扫描 (XCT) 表征。观察和跟踪各个阶段的碳化物、气孔和裂纹的演变。为了量化 3D 微观结构，提出了一种将断裂表面形态与裂纹演化行为相关联的新损伤因子。发现在疲劳试验期间，孔隙率比碳化物在裂纹萌生和扩展方面更有害。此外，在裂纹萌生阶段，孔间距是所有控制孔隙特征的最重要因素，而球形度是裂纹扩展阶段最关键的孔隙特征。因此，本研究通过对疲劳试验过程中碳化物和气孔的演变进行统计分析，揭示了镍基高温合金的潜在疲劳开裂机制。