b'Figure 2. Loading Cr coatedinside of the cracks was investigatedsample biasing a compressive residual SiC coupons for an X-rayby using focused ion beam milling tostress can be imparted into the sample. diffraction residual stressboth expose crack cross-sections, asDCMS coatings produced by Adele measurement at ORNL.well as fabricate liftouts for ScanningEvans at MMU with various levels Transmission Electron Microscopyof compressive residual stress were (STEM)/ Energy Dispersive X-Raycharacterized at ORNL. It was found Spectroscopy (EDS) characterizationthat 0.8 GPa of compressive stress by Daniel Morral. It was observedcan be imparted into coatings before that the corrosion rate on both theadhesion is affected. If compressive surface and interior of the crack wasstresses become too large the SiC will too low to form an oxide layer in aform microcracks reducing the coating reasonable amount of time (Figureadhesion. Previous work at ORNL 3). Additionally, due to the stressshowed that tensile stress cracking and distribution cracks will be wider at thespallation initiates above ~0.35 GPa of base further hindering this process.tensile residual stress so a large stress Therefore, coatings must be designedbuffer can be built into the coating. which stop the formation of cracks.Toughening the coating to either blunt By changing the kinetic energy ofor deflect cracks was the other strategy the ions during deposition throughinvestigated. Nanoindentation and 64 2020|AFC ACCOMPLISHMENTS'