Basic study on self-healing of Er2O3 coating for vanadium–lithium blanket system

Development of ceramic coatings at inner wall of duct tubing is strongly required for self-cooled lithium/vanadium-alloy (Li/V-alloy) blanket concept to reduce magneto-hydrodynamics (MHD) pressure drop. In our previous study, erbium oxide (Er2O3) coatings fabricated by physical vapor deposition (PVD) method showed high electrical resistance and high compatibility with liquid lithium (Li). In situ formation of Er2O3 coatings was also explored to show oxygen in the V-alloy substrate and Er dissolved in Li could react to form thin Er2O3 layer at the interface. In this study, feasibility of self-healing of Er2O3 coating is explored by observing its in situ formation at cracks on the coatings fabricated by PVD method. V–4Cr–4Ti substrates were oxidized at 973 K for 6 h and annealed at 973 K for 16 h to introduce proper amount of oxygen into the substrates. The coatings deposited at room temperature (R.T.) were uniformly flat. On the contrary, the coatings deposited at 873 K had peeled off at most areas. After introducing cracks on Er2O3 coatings by heating, the samples were exposed in liquid Li doped with Er at 873 K for 100 h and afterward at 973 K for 100 h to heal the cracks. At the large peeled-off areas, no in situ formation was observed, while the small cracks were healed. Peel-off of the coating indicates the intrusion of Li between the coating and the substrate. For improvement of self-healing of Er2O3 coatings, it is essential to progress in the adherence of them to the substrates and control the surface condition of the substrates.