The role of cyclic oxidation on low cycle fatigue crack initiation and growth behaviour of a Ni-based superalloy

Low cycle fatigue (LCF) resistance of Ni-based superalloys plays a pivotal role in optimizing the design and life of the turbine blades under oxidizing conditions. It is essential for ensuring long term reliability and structural integrity. In this study, the author presents experimental evidence of oxygen ingress during LCF deformation of directionally solidified (DS) CM 247 alloy at 850 degrees C, highlighting its detrimental effects on crack initiation and growth mechanisms. Compositional analysis revealed that the NiO, Cr2Os, and Al2Os oxide layers formed on the surface, which cracks during cyclic loading, leading to early crack initiation. Additionally, oxygen ingress through these cracks accelerates crack propagation. Early crack nucleation and accelerated crack growth contribute to a reduced LCF life.