b'Figure 3. Cross section of HiPIMSusing SEM, as shown in Figure 1. Thehave similar thermal diffusivity as and cold spray Cr coating afterHiPIMS Cr coating demonstrates auncoated Zircaloy, and cold spray Cr thermal aging at 750C. Largerdense microstructure, with no observ- coated Zircaloy shows the reduced voids were observed at the interface or within the coatings able porosity in the coatings. The coldaverage thermal diffusivity by ~5-7% spray Cr coating exhibits some largerthan the uncoated Zircaloy. The slight pores (up to ~1 m) and crack-likereduction of thermal diffusivity in defects, with some examples labelledcold spray Cr coated Zircaloy is not in Figure 1b. Smaller pores in Crattributed to its thicker Cr coatings coatings are also observed in higherdue to the higher thermal diffusivity magnification image in Figure 1d.of pure Cr than Zr but could be attrib-Such porosity could be attributeduted to the porosity in the cold spray to the high supersonic velocities ofCr coating as seen in Figure 1.powder particles that was depositedThe microstructure of Cr coated on the substrate surface, whichZircaloy after thermal aging at 750C could cause imperfect bonding. was characterized. Figure 3 shows the As-deposited Cr coatings has minormicrostructure of the HiPIMS and effects on the thermal diffusivity of Zrcold spray Cr coated Zircaloy after the cladding. Figure 2 shows the temper- aging for 2800 hours at 750C. HIPIMS ature-dependent thermal diffusivityCr coatings has maintained the dense of as-deposited Cr coated Zircaloy upmicrostructure with no coating to 700C, in comparison to uncoateddelamination. Voids are observed at Zircaloy. Three measurements werethe coating/substrate interface. The performed on the cold spray Crformation of such voids is likely due coated Zircaloy, and the results areto the counter flow of vacancy in consistent, with the variation belowresponse to mass transport across an ~2-5%. HiPIMS Cr coated Zircaloyinterface (in this case Cr diffusion to 38 2023|AFC ACCOMPLISHMENTS'