A Modified Focused Ion-Beam Milling Approach to Reveal Subsurface Features of Plasma-Sprayed Ceramic Splats

Abstract This work presents a modified approach to Focused Ion Beam (FIB) milling, specifically tailored to preparing cross-sections of plasma sprayed resolidified ceramic splats, was developed at the Center for Thermal Spray Research at Stony Brook University and refined at the Forschungszentrum Jülich Thermal Spray Center. Two key advantages were gained from this modified approach: relatively large (100 µm long by 25-50 µm wide by 5-10 µm deep) ion-milled trenches were possible in as little as several hours of milling time and the traditional platinum overcoat was deemed not necessary. Images of single and double-splat cross-sections show the through-thickness crack propagation of mudflat cracks. Refinement of this method allowed for even shorter (up to or less than one hour) milling times for splat cross-section viewing, and concurrent Energy Dispersive Spectroscopy for chemical analysis of unique splat combinations of Thermal Barrier Coating (TBC) splats atop Environmental Barrier Coating (EBC) splats. Additionally, time-lapse imaging during the ion-milling process garnered additional insights about subsurface features within the splats. The results in this paper and the time-lapse animations online revealed subsurface ‘bubbles’ embedded in EBC splats—dependent on the process parameters. Finally, the TBC-on-EBC splat cross-section points toward the presence of viscous flow of solid amorphous EBC material during microsecond solidification of a molten TBC splat.