Proceedings of the 3rd International Symposium on High Temperature Corrosion and Protection of Materials
Actes du 3ème Colloque International sur la Corrosion et la Protection des Matériaux à Haute Température

J. Phys. IV France 03 (1993) C9-865-C9-871
DOI: 10.1051/jp4:1993989

Improved SiO₂-coatings against high temperature sulphidation by internal stress reduction

R. Hofman¹, J.G.F. Westheim², T. Fransen³ and P.J. Gellings<sup>2

1</sup>  University of Twente, Department of Chemical Technology, Division of Corrosion Science and Inorganic Chemistry, PO. Box 217,7500 AE Twente, The Netherlands.
²  University of Twente, Department of Chemical Technology, Division of Corrosion Science and Inorganic Chemistry, PO. Box 217, 7500 AE Twente, The Netherlands.
³  To whom all correspondence should be addressed.

Abstract
Alloys such as AIS1 304 and AIS1 321 stainless steels and Incoloy 800H can be protected against high temperature corrosion by means of amorphous SiO₂-coatings deposited by metal organic chemical vapor deposition (MOCVD). The coated alloys are only attacked locally after exposure to a 19% H₂, 1% H₂S, 1.5% H₂O, Ar bal. environment at 823 K (p_S2 = 1.2 x 10^-9bar and p_O2 = 9.3 x 10^-29 bar). The crack density observed after sulphidation is identical for silica deposited onto all metallic substrates. Decohesion of amorphous silica coatings from AISI 304 is observed, when the coating thickness exceeds 1.7 µm, while coatings on Incoloy 800H are adherent up to 4 µm. These phenomena can be explained by the fact that the adhesion is a function of the chemical interactions between the metal and the coating, whereas crack formation is only a function of the internal stresses in the coating. Two methods are studied to reduce the coating failure by means of a reduction of internal stresses in the coating, the first is changing the deposition process and the second is reducing the thermal mismatch between the coating and the metal.

© EDP Sciences 1993