Competitive cracking behavior and microscopic mechanism of Ni-based superalloy blade respecting accelerated CCF failure

The cracking behavior and microscopic mechanism of K403 superalloy turbine blade are investigated respecting the Combined high and low Cycle Fatigue (CCF) with four acceleration states. It concludes that: (1) the crack initiation sites transform from slip planes inside alloy matrix to subsurface pores and carbides, then to oxides outside surface with increasing loads; (2) the behavior in (1) is attributed to the competition and alliance of different microstructural factors and the interaction of the factors with grain boundaries; (3) hereinto, the role shift of high cycle fatigue in CCF causes the transformation of transgranular to intergranular cracking mode.