Nanostructured surface layer and high-cycle fatigue behavior at 850 °C of single-crystal nickel superalloy induced by surface grinding treatment

Abstract

The microstructures in the surface layer by surface grinding treatment (SGT) and their fractographic features in high-cycle fatigue (HCF) at 850 °C are investigated for single-crystal nickel superalloy (SCNS) DD6. All samples after SGT show the nanostructure transition from single crystal to polycrystalline grains. Furthermore, the sample with nano-sized grains (∼60 nm) and a defect-free grinding surface suppresses fatigue crack initiation and exhibits large facets on the fracture surface; however, the sample with large grains and many grinding surface defects shows the tiny cleavage step fracture initiated from multiple fatigue source sites. The fractographic features indicate that the quasi-cleavage fracture mechanism dominates high-cycle fatigue behavior at 850 °C of the ground DD6 sample.