A study of high cycle fatigue life and its correlation with microstructural parameters in IN713C nickel-based superalloy

IN713C nickel-based superalloy is widely used in the form of turbine blades in the automobile industry. High cycle fatigue (HCF) or very-HCF is one of the major failure modes for the alloy. The significant grain structure/ size variations produced during the casting process are supposed to affect its fatigue life. In the present study, IN713C cast bars with different grain structures and grain size were HCF tested under similar stress level (-300 MPa) at 650 degrees C. The fatigue life, varying from-87,000 to 10 x 106 cycles, mainly determined by the size of porosity and faceting grain. Size of porosity determines the time of initiation of faceting and crack, i.e., the crack initiation stage, which occupies the major part of fatigue life. Smaller pore size leads to delay of faceting and higher fatigue life. Whilst size of facet has profound effects in the crack propagation stage. Smaller facet (grain) size leads to lower crack propagation rate and longer loading cycles, and finally contributes to higher fatigue life. This research revealed the beneficial effect of smaller grain size on fatigue property from the perspective of reducing initial crack propagation rate, which has rarely been reported before.