Nickel-base superalloys characterized by SLAM after long term heating

The effects of long term heating for up to 49 000 hours of Nickel-base polycrystalline (INCONEL 738) and single crystal (CMSX-4) superalloys are studied by the change of the acoustic attenuation (investigated by Scanning Laser Acoustic Microscope-SLAM) caused by variations in the microstructure (investigated by SEM) after mechanical and thermal fatigue. The aim of this work changes in the microstructure (phase transformation, creation of carbides at the grain boundaries, etc.) of the Inconel 738 and the change in the acoustic attenuation in order to characterize the embrittlement of the structure. In fact by using SLAM technique it is possible to obtain useful information not only about the presence of defects, but also on the change of the microstructure thanks to the use of acoustic images.