In many metallic materials such as Inconel superalloys, the microstructure and grain size play an important role in their mechanical and physical properties and could impact the performance during long-term service at the operational temperature. Therefore, on-site detection of the microstructural transformation (such as recrystallization and grain growth) is of primary importance from a structural integrity point of view. Nondestructive evaluation methods such as the ultrasonic attenuation measurement offer a unique advantage that they can be used to evaluate the microstructure evolution of a component during fabrication or service operation. Nondestructive determination of the grain size could help predict the mechanical behavior of the component. In this study, the measured attenuation coefficient was fitted to a theoretical attenuation model to establish the grain size, which shows a strong quantitative agreement with the grain size determined from Electron Backscatter Diffraction (EBSD) analysis. Furthermore, the EBSD texture results confirmed the existence of a recrystallization temperature region previously established using hardness measurements. This experimental evidence demonstrates that ultrasonic attenuation can predict the grain transformation that could occur during material processing or operational service.
Keywords: Attenuation coefficient; EBSD; Grain size; Inconel 625; Inconel 718; Recrystallization; Ultrasound.
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