Ceramic coating for corrosion (c3) resistance of nuclear fuel cladding

In an attempt to develop a nuclear fuel cladding that is more tolerant to loss-of-coolant-accidents (LOCA), ceramic coatings were deposited onto a ZIRLO (TM)(1) substrate by cathodic arc physical vapor deposition (CA-PVD). The coatings consisted of either Ti-1 _ xAlxN or TiN ceramic monolithic layers with a titanium bond coating layer as the interlayer between the ceramic coating and the ZIRLO (TM) substrate to improve coating adhesion. Several coating deposition trials were performed investigating the effects of bond coating thickness (200-800 nm), ceramic coating thickness (4, 8 and 12 mu m), substrate surface roughness prior to deposition, and select coating deposition processing parameters, such as nitrogen partial pressure and substrate bias, in order to optimize the coating durability in a corrosion environment. Corrosion tests were performed in static pure water at 360 degrees C and saturation pressure (18.7 MPa) for 3 days. The optimized nitride-based ceramic coatings survived the autoclave test exposure showing very low weight gain of 1-5 mg/dm(2) compared to the uncoated ZIRLO (TM) samples which showed an average weight gain of 14.4 mg/dm(2). Post-corrosion exposure analytical characterization showed that aluminum depletion occurred in the TiAlN coated samples during the autoclave corrosion test, which led to the formation of the boehmite phase that degraded the corrosion durability of some of the TiAlN samples. However, by eliminating the aluminum content and depositing TiN, the boehmite phase was prevented from forming. Best results in TiAlN coated samples were obtained with 600 nm Ti bond coating thickness, 12 mu m coating thickness and 0.25 mu m substrate surface roughness (E14). Results are discussed in terms of the capability of TiN and Ti-1 _ xAlxN coatings to improve the high temperature corrosion resistance and oxidation resistance of zirconium alloy cladding. (C) 2015 Elsevier B.V. All rights reserved.