Forming an overlayer on the ceramic coating with ductile metals is an alternative approach to in situ healing to compensate for cracks in the insulator layer. Current efforts for fabricating the two-layer
coating use pure V, V-alloys, and pure Fe, as shown in Figure 9. In these cases, only modest compatibil­ity with Li would be required for the insulator ceramics. Instead, the compatibility of V, V-alloys, and pure Fe with Li needs to be verified. It is also necessary to avoid shorting between the over­layer and the substrate. The Er2O3-V and Y2O3-V two-layer coatings on a V-alloy substrate fabricated using the EB-PVD process showed sufficient resis­tivity in Li.31

Recently, a mono-metallic thermal convection Li loop was constructed using V-4Cr-4Ti alloy. The two-layer coatings were tested in addition to uncoated V-alloy substrates at 700 °C for >2000 h in flowing Li. The tentative results showed that the corrosion loss, degradation of the coating, and mechanical property changes to the substrate were small.32 However, a full characterization remains to be completed.