4D micromechanical fatigue investigation of polycrystalline nickel superalloy – MINIFAT-4D

The fatigue life of structural alloys can vary over several orders of magnitude under identical loading conditions. This dispersion can be largely attributed to the variability inherent at the material microstructure. Indeed, fatigue damage proceeds from the accumulation of localized plastic strain at a subgranular scale, which is highly dependent on the morphology and orientation of grains in metallic materials. Currently, this dispersion accounted for only qualitatively by microstructure sensitive fatigue life models. The goal of the MINIFAT-4D AnR project is to quantitatively link the intragranular localization of plastic slip to the fatigue lifetime, in the view of achieving accurate predictions of microstructure influence on fatigue life and variability. For that, the project will rely, on the one hand, develop a new experimental set-up, consisting of an in-situ 3D characterization of fatigue tests using synchrotron X-ray diffraction based scanning tomography techniques (DCT, 3D-XRD, topotomography). These experiments will allow to simultaneous characterize the microstructure, the microscopic plastic/elastic strains, and the fatigue crack initiation and propagation of nickel based superalloy samples, with a submicron resolution. On the other hand, a new gradient crystal plasticity framework will be designed to accurately predict to predict the formation and intensity of individual slip bands within the studied material. It will then be used to simulate the microstructures studied during the 4D tests, to enable experiments and simulation full-field comparisons, used for the inverse identification of the crystal plasticity model, and to derive predictive criteria for the location and time of crack nucleation and propagation. Overall, we expect that the project will further the understanding of fatigue at the microstructural scale and open the way towards predictive microstructure sensitive fatigue models.