Effect of cold expansion on high-temperature low-cycle fatigue performance of the nickel-based superalloy hole structure

Low-cycle fatigue properties before/after cold expansion under multiple conditions were comparatively researched. The results showed the fatigue cycles of the cold-expanded specimens are more than doubled compared to the original, and the fatigue gain decreased as the stress increased. Surface smoothing, surface compressive residual stress field, and cold work-hardened structure with the sub-grain refinement were recognized as the main reasons for increasing the initiation life. The relatively stable compressive residual stress under 400 degrees C aging and 820 MPa/RT limited the crack propagation, making the width of the fatigue band and the crack propagation speed of cold-expanded specimen smaller than hole-reamed at the same depth.

Automated summary

The research showed that the fatigue life of cold-expanded specimens is more than doubled compared to the original, and the fatigue gain decreases with increasing stress. The cold-expanded specimens have compressive residual stress and cold work-hardened structure, which increase the initiation life and inhibit crack propagation under high temperature and stress.