The microscopic mechanism of high temperature (900 °C) fatigue crack growth in a single crystal Ni-based superalloy is investigated. Particular attention is focused to its relation to the cyclic misorientation markings (CMMs), formerly termed EBSD (electron backscattered diffraction) striation, left along the crack wake. Observation of a cross-sectioned crack tip is conducted by various electron microscopy i.e. SEM, EBSD, high-voltage TEM and STEM-EDS. A {100} fatigue crack subjected to a relatively high ΔK (40 MPam^1/2) shows CMMs with an interval corresponding to crack growth rate (2–4 μm/cycle), consisting of heavily dislocated γ (Ni) phase and less dislocated γ’ (Ni₃Al) phase. It is also revealed that local oxidation along the γ/γ’ interface at the crack tip existed at the current temperature/ΔK level. On the bases of these findings, a rational yet qualitative crack growth model that incorporated both brittle/ductile processes is proposed.

研究了单晶镍基高温合金中高温（900℃）疲劳裂纹扩展的微观机理。特别关注的是其与沿裂纹尾波留下的循环取向错误标记（CMM）（以前称为EBSD（电子背散射衍射）条纹）的关系。通过各种电子显微镜，即SEM，EBSD，高压TEM和STEM-EDS观察横截面的裂纹尖端。经受相对较高的ΔK（40 MPam ^1/2）的{100}疲劳裂纹显示CMM的间隔对应于裂纹扩展速率（2-4μm/周期），由位错严重的γ（Ni）相组成，并且位错γ'（Ni ₃Al）相。还揭示出在当前温度/ ΔK水平下，沿裂纹尖端的γ/γ′界面存在局部氧化。在这些发现的基础上，提出了结合了脆性/延性过程的合理而定性的裂纹扩展模型。