Highly Efficient Thermal Barrier Coatings Based on Arc Spraying of Amorphous Fe-based Alloys and NiCrAlY for Use in LH2 Tanks and other Cryogenic Environments

In the current work, a typical NiCrAlY alloy and two novel amorphous Fe-based alloys were arc-sprayed for the desired application as insulative coatings in cryogenic environments such as for the inner walls of LH2 tanks. For the experiments, nitrogen was used as process gas, while the stand-off distance and number of passes were varied. The deposition efficiency, tensile adhesive strength, hardness, durability under cryogenic conditions, and thermal diffusivity were investigated. Another focus included the visual and chemical characterization of the microstructures and potential changes in these due to the harsh temperature regime. Additionally, the residual stresses within the coatings were measured by the incremental hole drilling method based on electronic speckle pattern interferometry and correlated with the other coating properties. This was done to estimate the influence of the stress state on possible coating delamination in the tanks over a longer period. The results demonstrate coatings with low, but varying porosity and oxide content as well as material-dependent correlations to electrical conductivity. In particular, the amorphous Fe-based coatings reveal homogeneous coating structures and promising properties in terms of insulation capacity for use in various cryogenic applications.