In situ synchrotron X-ray imaging of high-cycle fatigue crack propagation in single-crystal nickel-base alloys

• Published in: Acta materialia Vol. 59; no. 13; pp. 5103 - 5115
• Main Authors: Liu, L., Husseini, N.S., Torbet, C.J., Lee, W.-K., Clarke, R., Jones, J.W., Pollock, T.M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-08-2011; Elsevier
• Subjects: Applied sciences; Crack propagation; Cracks; Driving; Exact sciences and technology; Fatigue; Fatigue failure; Finite-element analysis; Fracture mechanics; High-cycle fatigue; Imaging; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Nickel alloys; Nickel base alloys; Single crystals; X-ray diffraction; X-ray diffraction; Nickel alloys; Finite-element analysis; High-cycle fatigue; Nickel base alloys; In situ; Mechanical properties; Fatigue; X ray diffraction; Modeling; Single crystal; Fatigue crack; Crack propagation; Finite element method; Imaging
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2011.04.042

Fatigue crack propagation in single-crystal nickel-base superalloys was studied in situ with synchrotron X-ray imaging in a very high-cycle regime. Experiments were performed at ambient temperature with a newly developed portable ultrasonic fatigue instrument. The fatigue apparatus produced stable fatigue crack propagation with positive mean stresses for specimens as thin as 150
μm at a loading frequency of 20
kHz. Fatigue cracks propagated in a mixed-mode crystallographic manner along {1
1
1} slip planes. Phase-contrast imaging permitted analysis of the interaction of the crack front with microstructural features. Three-dimensional linear elastic finite-element analyses were performed to investigate the driving forces for crack propagation in the sheet specimen geometry. For the experimental conditions examined, fatigue crack growth is driven by the resolved shear and normal stresses on the active crack tip slip systems. An octahedral stress intensity is proposed as the relevant driving force for crack growth which determines the fatigue crack growth plane in nickel-base single crystals at room temperature.