The effect of defects on the fatigue crack initiation process in two p/m superalloys: part ii. surface-subsurface transition

The change in fatigue failure initiation sites from a surface to subsurface location for two P/M nickel-based superalloys is analyzed. In particular the influences of defect size, shape, and population on the elevated temperature fatigue processes are assessed. The analysis shows that at high strain ranges, crack initiation occurs rapidly, and crack propagation rates determine the fatigue life and failure site. As a result, defect location (related to population) and size are the more important parameters. At lower strain ranges, however, crack initiation is critical in determining the failure origin, and this is primarily controlled by defect shape.