Microstructural characterization of aircraft parts at different length scales
A Friction Stir Welded wing structure has been characterized in the scanning electron microscope (SEM) with backscattered electron imaging, energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). The microstructural changes around the weld are clearly visible in the EBSD images. However, EBSD does not seem to fully explain and reveal what causes the reduction in mechanical properties along the weldment. For instance, the stirred zone is the softest area despite having the smallest grain size. This implies that there are changes that take place at the nano-scale which are not visible by SEM and EBSD.
Also, within the stirred zone microstructural features are seen which indicate heavily stirred zones yet it is not clear what the differences are between these areas and the surrounding stirred zone, just from SEM imaging.
A transmission electron microcopy (TEM) study is done on different regions to reveal the differences with respect to the density of dislocations and other defects. Also, the recently developed technique of automated SEM and EDS acquisition is used to analyze the precipitate phases. Statistically meaningful information on precipitate size, shape and composition is compared between the base metal and different parts of the stirred zone and heat affected zone.