Abstract
The ability of hydrogen to permeate through composite systems consisting of metallic coatings on Type 304 stainless steel and Haynes 25 alloy as base metals was evaluated. Results indicate that the effectiveness of a particular coating-base metal system in retarding hydrogen passage can often be predicted qualitatively from knowledge of the metallurgical interaction between the coating and base metal. In systems where virtually no interaction or extensive solid solution effects occur, the coating produces a relatively small change in permeability. In systems where a continuous intermetallic layer is formed between the coating and base metal, e.g., aluminum, silicon, or metal-silicide coatings on Haynes 25 alloy, a significant decrease in permeability to hydrogen takes place.
