Abstract
Two Inconel 738 nickel base superalloy gas reactor turbine blades, in as-cast state and after operation, were compared by high-resolution Small Angle Neutron Scattering (SANS) at different positions along their edge, with the aim to assess the influence of high-temperature operation fatigue on the microstructure. Size distributions and relative volume fractions of γ´-precipitates were evaluated from measured SANS spectra for each blade and position. As results, the precipitate volume fraction increases towards both blades tips. The blade after operation exhibits a significant increase of precipitates average size and volume with respect to the as-cast blade, which can be explained by expected stronger precipitate coarsening under higher stresses. The precipitate size varied along the blade in the as-cast state. SANS provides a unique possibility of non-destructive characterization of precipitates in the turbine blades. The obtained results confirm the same method as a useful tool for fatigue testing in the considered industrial components.

Key words
Nickel base superalloy, precipitation, non-destructive testing, SANS, fatigue

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