Quantifying microscale drivers for fatigue failure via coupled synchrotron X-ray characterization and simulations.

Area of Science:

• Materials Science
• Metallurgy
• Solid Mechanics

Background:

• Crystallographic slip and deformation localization are key to fatigue crack initiation in metals.
• Coherent twin boundaries are critical sites for crack initiation in polycrystalline materials.
• Understanding 3D microstructural behavior under cyclic loading is essential for predicting material failure.

Purpose of the Study:

• To investigate deformation localization at the sub-grain scale near parent-twin boundaries in a nickel-based superalloy.
• To quantify the relationship between microstructural features and stress gradients.
• To elucidate the mechanisms leading to fatigue failure in these critical configurations.

Main Methods:

• Utilized a combination of high-resolution synchrotron X-ray characterizations.
• Employed dark-field X-ray microscopy, high energy X-ray diffraction microscopy, and X-ray diffraction contrast tomography.
• Integrated experimental data with crystal plasticity simulations for comprehensive analysis.

Main Results:

• Quantified intragranular misorientation and high elastic strain gradients near a twin boundary.
• Revealed extreme sub-grain scale stress gradients within the microstructure.
• Established a link between localized deformation and microstructural features.

Conclusions:

• Deformation localization at coherent twin boundaries is a precursor to fatigue crack initiation.
• Sub-grain scale stress gradients are significant drivers of fatigue failure in polycrystalline superalloys.
• Advanced X-ray techniques provide unprecedented resolution for characterizing critical microstructural phenomena.