High Temperature Protective Coatings of Interest to the Process Industry

Protective coatings are one approach to defend against corrosion at high temperatures and environments encountered in the process industry.  Halide Activated Pack Cementation is a versatile and economical method to apply such coatings.  Once the desired coating compositions have been identified, the coating process needs to be adjusted to obtain the final composition and microstructure.  Therefore, coating process optimization is an ongoing need.  In a typical process, the metallic component to be coated is placed within a mixture of powders that serve different roles, e.g., a master alloy that contains the coating element(s), a salt that participates in reactions to transport the coating elements to the surface of the material to be coated, and a filler that typically provides the framework for vapor transport.  The entire pack is processed in a high temperature furnace under flowing argon or argon-hydrogen mixtures.  One of the key parameters in achieving the desired coating is the arrival rate of the halide species at the substrate.  In this talk, key results from our modeling efforts will be presented.  Experimental results from our coating studies on Ni and Fe based systems will be discussed.