EDP Sciences Journals List
Issue J. Phys. IV France
Volume 03, Number C9, Décembre 1993
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
Page(s) C9-429 - C9-435
DOI http://dx.doi.org/10.1051/jp4:1993945

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) C9-429-C9-435

DOI: 10.1051/jp4:1993945

Sulfidation of pure and chromium-modified beta-NiAl intermetallic compound - mechanism studies

E. Godlewska and S. Mrowec

Institute of Materials Science, Academy of Mining and Metallurgy, al. Mickiewicza 30-059 Cracow, Poland


Abstract
The studies on sulfidation mechanism of pure and chromium modified [MATH]-NiAl intermetallic compound were carried out in He/S2 gas mixtures at high sulfur pressure (about 2 x 103 Pa). Gold markers were deposited on the surface of specimens prior to sulfidation run by a PVD process. The distribution of gold marker after sulfidation indicated that the outer scale layer, composed of sulfospinels, NiAl2S4 and/or CrAl2S4, and nickel sulfide, grows by an outward diffusion of cations. This is accompanied by an inward penetration of sulfur resulting in the formation of internal sulfides (Al2S3 and CrAl2S4). The inward transport of sulfur may be due to dissociation of the sulfospinel phases at the scale/alloy interface. Secondary formation of fine-grained sulfospinel phases was observed in the vicinity of the scale/alloy interface. Another secondary reaction takes place between the sulfospinels and nickel sulfide nodules present on the scale surface, greatly contributing to the overall growth of the sulfospinel layer on β-NiAl, NiAl-4Cr and NiAl-10Cr. The formation of a stratified scale on NiAl-20Cr is explained by periodic detachment of the scale layers and their reproduction on the alloy surface due to inward penetration of sulfur.



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