Ikeda and Nii Oxidation of Metals, Vol. 12, No. 6, 1978 pp 487 - 502
Uses "sulfur decoration" to study the distribution and time of generation of cracks in FeCr alloys and their oxides. Fe5Cr, Fe10Cr, and Fe20Cr were studied. They were studied at 750 and 900C. in pure O2. At the end of the oxidation H2S was introduced. Then the samples were cooled in Ar.
The Fe5Cr showed penetration of S all along the metal oxide boundary at 750C for 5 hrs. At 25 hours, a slight penetration to the metal oxide interface was seen. Thus, the oxide cracks were being filled. However, later cracking can be observed. Cr is enhanced at the inner oxide. Similar results are seen at 900C.
The Fe10Cr showed duplex oxide and different thickness of oxide at 750C. The thin oxide was Cr enriched. Cr depletion is observed, and so cracked oxide is aggressively attacked. They claim initial oxide behavior drives resistance to oxidation.
Fe20Cr at 900C shows a Cr2O3 oxide layer. Cracking was observed, but S intrusion was minor, suggesting the cracks rapidly healed. At long times (200hrs+) iron oxides were observed, but did not change the Cr dominated oxide layer.
The article 6 - Y. Ikeda and Nii, Trans. Jpn Inst. Metals 18, 471 (1977) should be obtained.
Summary by Allen