Synchrotron Microbeam Diffraction Study of the Microstructure and the Chemical Composition in a Monocrystalline Ni-Base Turbine Blade After a Thermomechanical Mission Test

Abstract

High-performance turbine blades composed of monocrystalline Ni-base γ/γ′ superalloys are often protected by coatings to resist the high-temperature corrosive atmosphere environment applications. During applications severe thermal and mechanical loads cause drastic and complicated changes in the microstructure and the chemical composition, also combined with strong lateral gradients of both temperature and stress. Microbeam X-ray diffraction experiments with a spatial resolution of about 5 μm enabled the determination of both the microstructural and the chemical composition gradients within material volumes of the sizes of the order of about 1 mm3 or smaller. The high angular and spatial resolution was achieved by a special focusing technique using a Bragg–Fresnel focusing monochromator at the BM5 beamline of the ESRF synchrotron at Grenoble. The X-ray diffraction experiments were complemented and supported by electron microscopy investigations of the microstructure and the chemical composition.