11/4/2023 0 Comments Far field diffraction definitionTo obtain three dimensional spatially resolved results with these latter techniques requires that samples be sectioned. Conventional experimental methods either lack sufficient spatial resolution or are surface or thin foil probes. The arrangement is often highly heterogeneous, especially with respect to dynamics during processing. The microstructure of polycrystalline materials is characterized by a hierarchical arrangement of crystalline elements (grains, microbands, and subgrains). In conclusion, appropriate conditions for crack nucleation in the form of stress gradients were demonstrated and created by virtue of the inclusion, specifically the residual stress state and local bonding state at the inclusion-matrix interface. Elasto-viscoplastic fast Fourier transform simulations were utilized to supplement interpretation of the experimental stress distributions and compared with the experimental stress distributions. Strain partitioning and the associated stress heterogeneities that develop are shown to stabilize within a few loading cycles. The µ-CT data showed the onset and location of crack initiation, and the FF-HEDM data provided temporal and spatial evolution of the intergranular strains. Sequential μ-CT and FF-HEDM scans were carried out at both peak and zero applied stress following schedules of cyclic deformation. Two x-ray techniques were employed: absorption contrast computed micro-tomography (μ-CT) to determine the morphology of the inclusion and its location in the gauge section of more » the specimen and far-field high-energy diffraction microscopy (FF-HEDM) to resolve the centroids, average orientations, and lattice strains of the individual grains comprising the microstructure surrounding the inclusion. The specimen was produced via powder metallurgy and seeded with a non-metallic inclusion. In this study, fully 3-D characterization methods using high-energy synchrotron x-rays are combined with in-situ mechanical testing to study the crack initiation mechanism in a Ni-based superalloy specimen. Fatigue progresses in a complex manner to find the ‘weakest link’ in the microstructure, leading to crack nucleation. = ,Ĭrack initiation at inclusions is a dominant, unavoidable and life-limiting failure mechanism of important structural materials.
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