4D Micromechanical investigation of fatigue crack nucleation mechanisms in a polycrystalline nickel superalloy.

This works aims at understanding the interaction between microstructure, plasticity and fatigue damage in the nickel-based superalloy Inconel 718, by coupling several in-situ 3D characterisations techniques. The combination of Diffraction Contrast Tomography (DCT and 3D-XRD), Phase Contrast Tomography (PCT) and Topotomography (TT) are used to characterise the polycrystalline microstructure (DCT), the in-situ evolution of deformation heterogeneities (3D-XRD, TT) and damage (PCT) in micro-tensile specimens under fatigue loading. In-situ experiments at ESRF will be carried out with the NANOX test rig, specifically designed for high cycle fatigue testing on beamline ID11. A specific objective of this work will be to correlate the microstructure and the intragranular elastic and plastic deformations, to the onset of fatigue damage, with the aim of significantly improving the understanding of fatigue crack nucleation mechanisms.