Novel Fe- and Ni-based HVOF-sprayed coatings compared to APS-sprayed TBC systems for improved thermal insulation capabilities in cryogenic environments

Thermal sprayed coatings can be a potential core technology for the energy transition in several industrial areas. For example, there is currently no expertise in offshore production, storage, and transportation of large quantities of liquid hydrogen (LH2) due to the emerging market. As a result, present tank designs refer to standard onshore designs with thick walls and insufficient thermal insulation. This leads to lower cost efficiency due to boil-off and neglects some other demands such as mechanical and cyclic durability. Consequently, thermal barrier coatings (TBC) are attracting interest due to high insulating effects and wear resistance to counteract boil-off and additionally protect the inner tank shell from dynamic sloshing forces. A key factor influencing the thermal properties is the defect content of such coatings.

Thus, a NiCrAlY alloy and Fe-based alloys are HVOF-sprayed due to the combination of high coating density and customizable coating properties. The oxygen/fuel gas ratio was varied to modify coating defects in a targeted manner. In parallel, the coatings were compared with APS-sprayed TBC systems based on NiCrAlY and NiCrAlY+YSZ. The results demonstrate low porosity and oxide contents. Further investigations regard the thermal diffusivity, residual stresses, hardness, electrical conductivity, and durability under cryogenic conditions.