Fatigue Crack Initiation and Propagation in Superalloy IN 713LC

High-cycle fatigue life of cast Ni-base superalloy IN 713LC under load symmetrical cycling and cycling with tensile mean stress was experimentally determined. The fatigue life exhibits very large scatter. Both crystallographic Stage I crack propagation and non-crystallographic Stage II propagation were observed. High scatter of fatigue life data was explained by (i) variability in microstructural conditions for crystallographic crack initiation and propagation and by (ii) influence of casting defect size distribution. The fractographic observation supports the slip band decohesion model for crack initiation and early crack propagation and important role of cyclic slip localization in persistent slip bands.