Coatings for use in liquid metals

The targeted modification of properties on the surface of a structural material can extend its service life in the event of external stresses acting on the material. The change that can be achieved by creating a layer of a second material is the most striking. In addition to the function, the adhesion of the coating to the substrate in particular must be guaranteed and must be permanently maintained under the stress of the composite in the case of use.

For metallic materials in the presence of liquid metals, corrosion protection is usually of overriding importance. If there is a minimum of oxygen dissolved in the liquid metal, corundum (a-Al2O3) or coatings forming this oxide are particularly suitable.

Currently developed coatings for steel are based on galvanic deposition of aluminium from an ionic liquid and a three-stage heat treatment, during which the aluminium dissolves in the zone near the surface of the steel and aluminium oxide grows on the surface. The oxygen required for this comes from the gas atmosphere in the annealing furnace.

The work is connected with the development of the fusion reactor, for which certain components must be protected against corrosion by a liquid lithium-lead alloy. At the same time, the surface must be electrically non-conductive and, in particular, the passage of tritium through the component wall must be reduced. Alumina can fulfil all three functions.