Preparation Of Hot Dip Aluminized Stainless Steel Container Surface Aluminide Coatings And Its Infiltration Deuterium,

Tritium induce radiation in reactor materials and some radioactive tritium gas may be released.Most of the materials used in the ITER-test blanket module fusion reactors is stainless steel that is ductile and strong enough but have relatively high permeabilities for tritium. Researchers have been working on the permeation reduction barriers for a long time. In the design description document composed by the work group the minimum tritium permeation reduction factor in the working environment was set as 100 at 500℃.In the first chapter of this paper the status of tritium permeation barrier as well as the preparation ways of aluminide coatings was presented briefly and then hot dip aluminizing with the oxidation methods, the mechanism of the permeation in the barriers, the test methods of the permeation were reviewed. Consequently, aluminide coatings was selected to be prepared on the 1Cr18Ni9Ti steel tubes through hot dip aluminizing to reduce the permeation.In the second chapter, the micro structure, composition as well as the phase of the hot dip coatings were studied by scanning electron microcopy, energy dispersion X-ray spectrum, X-ray diffraction and X-ray photo electron spectroscopy, the thickness of the layers at different time and temperature were confirmed with metallographic microscope. It was found that the hot dip coatings were made up of top aluminum layers and inter layers which mainly contained intermetallics of FeAl3 and Fe2Al5.After all, The parameters were optimized. The dipping assistant agent and the covering flux were optimized as 6%KF+4%NaCl and 50%KCl+25%NaCl+17% NaF+8%AlF3 respectively. The growth kinetics of the intermetallic layers were then disscussed.It was indicated that the growth followed the parabolic law at 700℃,720℃,nevertheless,at higher temperature (740℃,760℃)the growth did not keep to the parabolic law any longer.In the third chapter, the morphologies of the surfaces were studied with SEM after the thermal oxidation treatment in air. At 600℃,the oxides gradually grew up and then form a film on the surface. While the temperature was higher than 650℃the oxide film cracked and flaked off, subsequently, the oxides grew up to a film again. From the XRD spectrum it was shown that intermetallics transformed from aluminum rich phase to aluminum poor phase as follows:FeAl3â†'Fe2Al5â†'FeAl2â†'FeAlâ†' Fe3Al. The thickness of the intermetallic layer suggested that both volume diffusion and grain growth controlled the growth of the interlayer.In the end the permeation rate of the coated tubes was tested with a simple but convenient system which is primarily built up of a helium mass spectrum leak hunter. The unoxidated aluminide coating exhibited poor ability to reduce the permeation whereas the sample heat treated in the air reduced the permeation rate for about 100 times.Meanwhile, the oxidized sample has a similar permeation activation energy to the bare samle. Particularly the vacuum oxidized sample had a higher permeation activation energy and its PRF accordingly reached 850 at 500℃and 89 at 700℃. The anode oxidized samples was also very effective at low temperature (500℃) as well for its PRF reached 750 but it was degraded rapidly when the coatings was working at a higher temperature.