Preparation Of Al₂O₃-TiC Coating As Tritium Permeation Barrier By Laser-assisted Combustion Synthesis

Permeation barrier coatings have been prepared on the surface of structural materials for preventing tritium permeation in fusion reactor. Hence, the research of tritium permeation barrier has significant meaning for the application and development of nuclear fusion energy.Al2O3-TiC composite coating as tritium permeation barrier was successfully obtained via laser-assisted combustion synthesis in this dissertation. The research contents were described as follows:The effect of laser energy density on the microstructure of the coatings was studied. The calculated laser energy density needed to trigger the combustion reaction was 20.83 J/mm2. When the actual laser energy densities were below 83.3 J/mm2, the obtained coatings were not dense, cracks were found in the coating-substrate interface, and the performance of the coatings were poor. When the actual laser energy densities were above 125.5 J/mm2, the performance of the coatings were moderate. When the actual laser energy densities were between 83.3 J/mm2 and 125.5 J/mm2, the obtained coatings were dense with improved performance.The effect of ball milling time in precursor material on the microstructure of the coatings was also studied. The powder mixture was more uniform after milling for 2 h than mixed manually. The crystal size of the powders decreased after milling. The structure in the obtained coating prepared by laser power of 4 kW and laser scanning speed of 6 mm/s was fine and uniform. The performance was superior to the coatings prepared with powders mixed manually or powders ball milled for longer period of time.When the laser power was 4 kW, the effect of laser scanning speed on microstructure and bonding strength of the coatings was studied. When the laser scanning speeds were above 20 mm/s, metallurgical bonding was not formed and the obtained coatings were fell off the substrates. The particle size in the coating structure increased with the decreasing laser scanning speed. When the laser scanning speeds were below 20 mm/s, metallurgical bonding was formed and the density of the obtained coatings increased with the decreasing laser scanning speed. When the laser scanning speed was 6 mm/s, the structure in the obtained coating was fine and uniform. The bonding strength of the coating was improved.The effect of pre-coating thickness on on the microstructure of the coatings was also studied. The microstructure of the coating transformed from large dendrites to fine equiaxed grains with the thickness increasing. The thermal shock resistance of the coatings were dependent on the pre-coating thickness.