The Analysis on the Low Cycle Fatigue Behavior of a Directionally Solidified Superalloy with Recrystallized Surface Layers
Specimens of a directionally solidified superalloy with different shot peening pressure were annealed at 1220oC in vacuum condition to get recrystallized surface layers with different micro-structures. Low cycle fatigue tests of these specimens were performed at room temperature and 400oC by using an electrohydraulic load frame in the SEM system for real-time observation. The initiation and propagation of cracks were inspected and the influence of the micro-structure of the recrystallized layer on the material fatigue behavior was analyzed. The low cycle fatigue life of the specimens depends mainly on the characteristics of the recrystallized layer. When the shot peening pressure is lower, the recrystallized layer is thin and not integrated, and the fatigue life decreases obviously in comparison with that of the specimen without recrystallized surface layer. When the shot peening pressure increases, the recrystal grains are more integrated, and the fatigue life rises. A comparison of the recrystallized layers between the blade surface and the specimen surface has been done and it points that the incompact surface recrystal layer is very dangerous to gas turbine blades.
Z.Y. Shen, M.N. James, W.D. Li, and Y.X. Zhao
H. J. Shi et al., "The Analysis on the Low Cycle Fatigue Behavior of a Directionally Solidified Superalloy with Recrystallized Surface Layers", Advanced Materials Research, Vols. 44-46, pp. 43-50, 2008