OS11(7)-27(OS11W0034) Microstructural Effects on Fatigue Crack Growth Behavior Near Threshold in a Ni-Base Superalloy

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Microstructural effects on near-threshold fatigue crack growth behavior in a Ni-based superalloy have been studied. TEM and SEM observations have been performed on corresponding microstructures near crack tip and fracture surfaces. The fatigue crack growth resistance increases with increasing grain size, i.e. the threshold value increases and the fatigue crack growth rate (FCGR) decreases; correspondingly the fracture surface changes from "fatigue striations" into remarkable "facets". However, increasing gamma prime phase size at age-peak condition leads to decrease of the fatigue crack growth resistance, i.e., the threshold value decreases and the FCGR increases; in this case the fracture surface shows "fatigue striations" feature. The high resistance to fatigue crack growth is closely related to the planar slip mode of dislocations in the plastic zone near crack tip, which gives rise to lower accumulation of damage and enhances crack closure resulted from facet-feature cracking. The optimum microstructure for best fatigue crack resistance is suggested as coarse grains with fine gamma prime phases just before age-peak is reached.
一般社団法人日本機械学会の論文
2003-09-09