Development of aluminum-alloy coating on type 316SS for nuclear systems using liquid lead–bismuth

An Al-alloy coating method using Al, Ti and Fe powders and the laser beam heating has been developed for nuclear systems using liquid lead–bismuth eutectic (LBE). Main defects formed in the coating process were surface defects and cracks. It was effective to decrease a laser beam scanning rate to 20mm/min to avoid surface defects. It was necessary to adjust the Al concentration in the coating layer to be lower than 12wt.% in order to avoid significant cracking. A static corrosion test was conducted in liquid LBE at the controlled oxygen concentrations of 10−6–10−3wt.% at 550°C for 3000h. The Al-alloy coating layer on 316SS prevented severe corrosion attack such as Ni dissolution, partial loss of grains and LBE penetration which were observed in 316SS without Al-alloy coating. Liquid LBE penetrated into the surface defects formed in the Al-alloy coating layers produced using a laser beam with the scanning rate of 60mm/min. The Al-alloy coating layer, which was formed without surface defects and cracks under the optimum condition of the scanning rate of 20mm/min, exhibited good corrosion resistance in liquid LBE.