Crack Initiation in Ni-Based Single Crystal Superalloy under Low-Cycle Fatigue-Oxidation Conditions

The mechanism of oxidation-assisted initiation of surface cracks of a fourth-generation Ni-based single crystal superalloy was systematically investigated during low cycle fatigue at 900 degrees C and 980 degrees C. The results show that cracks initiate near the surface defects at 900 degrees C, while they initiate in the surface oxide layer at 980 degrees C. At 900 degrees C, the oxidation microcrack initiation in the thicker inner oxidation layer is difficult to connect with the surface oxidation crack, which is an essential reason for the crack growth rate being slower and not becoming the main crack. At 980 degrees C, microcracks form in the outer oxide layer and quickly connect with microcracks at the surface and inner/outer oxide layer interface, growing into long cracks that become channels for rapid oxygen transport. This accelerates the crack growth rate, and eventually the oxide crack becomes the main crack.

Automated summary

The oxidation-assisted initiation of surface cracks in a fourth-generation Ni-based single crystal superalloy during low cycle fatigue at 900 degrees C and 980 degrees C was systematically investigated. The results showed that at 900 degrees C, cracks initiated near surface defects, while at 980 degrees C, cracks initiated in the surface oxide layer. In addition, microcracks in the outer oxide layer quickly connected with microcracks at the surface and inner/outer oxide layer interface at 980 degrees C. These cracks eventually became channels for rapid oxygen transport, accelerating the crack growth rate.