Influence of residual stress distribution and microstructural characteristics on fatigue failure mechanism in Ni-based Superalloy

The influence of residual compressive stress (RCS) depth and magnitude generated through surface treatments such as shot peening (SP), deep cold rolling (DCR), and vibro-peening (VP) on fatigue crack mechanisms of Ni-based superalloy is investigated. The fatigue performance with associated failure mechanisms is measured under strain-controlled fatigue testing upto 10(4) cycles with total strain in the range of 0.9%-1.4% at an R ratio of 0.1 and 400 degrees C followed by load controlled fatigue until failure. In-depth understanding of the failure mechanism is obtained through fractography analysis, cyclic stress-strain plot, and microstructural features. A pronounced improvement in fatigue life tested at low strain range (0.9%-1.1%) is achieved after inducing RCS up to 400 mu m depth. However, the fatigue life is reduced when RCS increased to 800-1000 mu m depth. Failure is primarily driven by micro-cracks formed due to balancing tensile stresses and high intensity stress concentration generated as the result of dislocation pile-ups and slip bands. Results are discussed in detail through the evidence of grain refinement, addition of low angle grain boundaries (LAGBs), strain accumulation, and intragranular deformation in the sub-surface.

Automated summary

This study investigated the influence of residual compressive stress (RCS) depth and magnitude generated through different surface treatments on fatigue crack mechanisms of Ni-based superalloy. The results showed a pronounced improvement in fatigue life at a depth of 400 μm induced RCS, but a reduction in fatigue life when RCS depth increased to 800-1000 μm. Failure mechanisms were primarily driven by micro-cracks formed due to balancing tensile stresses and high intensity stress concentration.