High Heat Flux Tolerant and Radiation Resistant Materials Based on Mo and SiC Coatings

Abstract

Fulfilling energy demand is very vital for every nation. But using fossil fuels to meet it has turned the global environment on a destructive path. The high level of greenhouse gas (GHG) emissions and the impacts of global warming have stimulated humans to find environmentally friendly energy practices. Apart from renewable sources, nuclear fusion and advanced nuclear fission are the aspiring alternative to fossil fuels. Scientists are considering fusion as a future of energy. The aim is the development of such a facility that can run the process for a long period of time. In order to sustain in a high-temperature plasma environment, it is needed to make plasma-facing components that are high heat flux tolerant and erosion resistive. Molybdenum (Mo) is a high Z refractory metal. It has a high melting temperature of 2617°C and a low coefficient of thermal expansion of 4.8 μm/m°C. Combination of thermo-mechanical and chemical properties makes it suitable for various applications that involve high heat flux. In Generation IV nuclear fission reactors, molten salt reactor will play a significant role in the exploration of nuclear energy. These reactors will employ graphite as a reflector and moderator. Owing to the high porosity of the graphite matrix, it undergoes oxidation at high temperatures. However, several opportunities exist to enhance graphite's utility as a moderator in Generation IV nuclear reactors. One of them is by developing an oxidation-resistant coating. This work consists of two major portions. At first, DC magnetron sputtering was employed to deposit molybdenum coatings on the graphite substrate. The impact of process parameters like sputtering power and working gas pressure has been investigated to get a suitable match between physical and mechanical characteristics of coating and substrate. Adequate class thin film was achieved at high deposition power and low working gas pressure. The optimum thin film was irradiated with He ion of 0.8 MeV and 1.6 MeV with an equivalent dose of 0.0765 and 0.645 DPA respectively. Different analytical techniques were employed to analyze the structure and morphological evolution occurred as a result of irradiation. Significant deterioration in crystallanity was observed as crystallite size was decreased at high irradiation dose. Surface roughness was increased and electrical conductivity was dropped. However, no delamination was observed. Micro-hardness of Mo thin film increased with an increase in irradiation dose. In the second part of this research one-micron silicon carbide (SiC) coating was developed on Graphite using RF VII Magnetron Sputtering to serve as an anti-corrosion layer. Crystallanity of deposited thin film was enhanced by high-temperature annealing at 1000, 1200 and 1400 °C. The dependence of corrosion resistance on the annealing temperature of coatings has been analyzed. Corrosion resistance of SiC thin film increased with an increase in annealing temperature as sample annealed at 1400 °C showed the lowest corrosion rate as compared to low temperature annealed thin films.