Effects of grain size on the high-cycle fatigue behavior of IN792 superalloy

The HCF (high-cycle fatigue) property of Ni-base cast superalloy IN792 with various grain sizes was investigated at 700 degrees C, 800 degrees C and 900 degrees C. The results show that grain refinement could improve the HCF lives since it could reduce the probability that "fatigue hot spots'' initiate near the surface. The improvement effect of grain refinement on the HCF life decreases with the increase of temperature and applied loading amplitude due to that the increasing of temperature and applied loading amplitude would cause a transition of "fatigue hot spots'' from the bulk to the surface or subsurface for fine grain specimens. The HCF deformation mechanism was studied through dislocation structure observation. At 700 degrees C, the movement of dislocations is restricted in the slip bands and the fatigue cracks form in a glide plane decohension manner, therefore it is easier to generate a fatigue crack for coarse grain specimens than fine grain specimens. As the temperature increased to 800 degrees C and 900 degrees C, the distribution of dislocations become more homogeneous and glide plane decohension is inhibited, so that the role of grain refinement on the HCF behavior is decreased. (C) 2014 Elsevier Ltd. All rights reserved.