Effect of substrate roughness and thermal cycling to the deuterium permeation of the MOCVD derived alumina coatings

Alumina coatings were deposited by MOCVD on 316L substrates. 316L substrates with surface roughness of 65.3 nm, 15.2 nm and 8.71 nm were used. The formation of amorphous alumina coatings was observed by XRD. The as-deposited coatings were uniform and continuous even on substrates with substantial trenches. The deuterium permeability of the as-deposited coating depended on the substrate roughness. Increased deuterium permeability of coating was illustrated as the substrate roughness increased. The permeability of the coating on 316L with roughness of 8.71 nm was 41–106 times lower than that of the uncoated 316L at 873–973 K. Furthermore, it was revealed that the thermal cycling resistance of coating related to the substrate roughness as well. The permeability of the coating on 316L with roughness of 65.3 nm exhibited an apparent increase after thermal cycling. While, there was no obvious change of permeability of coatings on the other two substrates. It was believed that the increase of permeability was mainly caused by the coating damage after thermal cycling. Therefore, it was concluded that substrate with low substrate roughness was favored to obtain the low permeability and high thermal cycling resistance of coating.