- Ece Alat, The Pennsylvania State University, University Park
The Fukushima-Daiichi accident motivated research for accident-tolerant fuels. The aim of my research was to develop ceramic coatings for zirconium-based nuclear fuel cladding that are corrosion resistant and that can withstand normal operation and accident conditions. Single layer TiN, single layer Ti1-xAlxN and multilayer TiN/Ti1-xAlxN coatings were deposited on flat and tubular samples of a commercially available substrate by using cathodic-arc physical vapor deposition (CA-PVD). Autoclave corrosion tests of the coated materials were performed in static pure water at 360°C and 18.7 MPa for up to 128 days. Following the autoclave test, weight gain analysis was used to characterize corrosion performance of the coated materials. Characterization methods used to examine the materials before and after the corrosion test include scanning electron microscopy for morphology examination, energy dispersive spectroscopy for elemental analysis, and x-ray diffraction to determine the phases present. Coating adhesion and corrosion performance was systematically improved through the optimization of parameters involving substrate surface preparation method, substrate surface roughness, titanium bond coating thickness, coating thickness, deposition parameters, and multilayer design architecture. We determined deposition parameter effects on coating morphology, composition, and adhesion; identified optimized CA-PVD parameters to enhance adhesion of the coatings on flat and tubular samples; and determined corrosion behavior of TiN and TiAlN in a nuclear reactor environment. The results indicated that the corrosion performance was substantially improved for the multilayer design and that the coatings enhance corrosion resistance under normal and extreme conditions.