Initiation and propagation behavior of fatigue cracks in 2197 (Al-Li)-T851 alloy

The initiation and propagation characteristics of the fatigue cracks were studied for 2197-T851 alloy. The results indicate that fatigue crack initiation is related to stress. Under smaller stress, fatigue cracks mainly initiate from the second phase particles and the interface between the second phase particles and matrix as well as from the surface defect. While with larger stress, fatigue cracks easily initiate from the grain boundary and the slip band. Fatigue cracks grow along the favorable slip plane with priority. When the favorable slip planes in the adjacent grains have an angle, the crack deflects. The coherent delta' particles that can be sheared by dislocation result in the crack path meandering in the grain. The cracks grow mainly in transgranular mode along the (111) plane, and also along the small-angle grain boundaries.