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A cross-sectional SEM micrograph of the structure of an 8-layer TiN/TiAlN coating produced by co-principal investigator Doug Wolfe (PSU) using magnetron sputtering. The image (obtained by Sickafus and co-workers at U. Tennessee) shows two identical ceramic coatings mounted face to face (the black region between the coatings is a layer of epoxy). The outermost layer of the multilayer coating is a pure titanium nitride (TiN) layer (the SEM contrast from this layer is relatively bright). Beneath the outermost TiN layer, the coating architecture consists of alternating titanium aluminum nitride (TiAlN) and TiN layers (the TiAlN layers are darker in contrast compared to TiN). The brightest layer at the bottom of the “stack” is a pure metallic Ti layer. This layer is used as a buffer layer between the ceramic coating and the cladding substrate (it improves coating adhesion to the substrate). The substrate in this particular image is silicon rather than zirconium alloy clad. The silicon is used as a control in coating deposition experiments to ensure that the layers are deposited uniformly and with the desired compositions. Accomplishments: In an attempt to develop an accident- tolerant fuel (ATF) with a cladding that can delay the deleterious consequences of loss-of-coolant-accidents (LOCA), multilayer ceramic coatings were depos- ited onto a ZIRLO© fuel cladding by cathodic arc physical vapor deposition (CA-PVD) and magnetron sputtering (DougWolfe, PSU).Various coating architectures composed of alternating TiN andTi1-xAlxN (2-layer, 4-layer, 8-layer and 16-layer) were deposited in order to investigate the minimumTiN top coating thickness necessary to avoid aluminum hydroxide phase forma- tion during corrosion and optimum coating architecture for good corrosion resistance and oxidation resistance. One type of 2-layer architecture consisted of a 1µmTiN top thickness (~1/10 of the total coating thickness), while other coatings were composed of layers with approximately equal thickness. Corro- sion tests were performed in static pure water at 360º C and saturation pres- sure (18.7 MPa) up to 90 days (Jonna Partezana,Westinghouse). Coatings having no spallation or delamination survived the autoclave test exposure with a maximum 6 mg/dm² weight gain, which is 6 times smaller than that of the uncoated ZIRLO™ sample which had a weight gain of 40.2 mg/ Coatings on nuclear fuel cladding may make reactors much safer, especially if coatings serve to arrest or slow cladding oxidation during a loss of coolant incident. dm². Post-corrosion exposure analytical characterization (PSU and U.Tennessee) showed that depositing ~1µmTiN as a top layer prevented aluminum hydroxide formation andTiN/TiAlN 8-layer architecture provided best corro- sion performance due to no hydroxide phase formation, approximately linear weight gain data without any delamina- tion/spallation and advanced oxygen ingress prevention. Multilayer TiN andTi1-xAlxN coatings have shown significant improvements in the high temperature corrosion resistance of zirconium alloy cladding.