The effect of microcrystallites in the amorphous matrix on the corrosion behavior of amorphous Fe-8Cr-P alloys

• Published in: Corrosion science 1995-09, Vol.37 (9), p.1411-1422
• Main Authors: Im, B.-M., Komori, M., Lee, B.-T., Aoyagi, E., Akiyama, E., Habazaki, H., Kawashima, A., Asami, K., Hiraga, K., Hashimoto, K.
• Format: Article
• Language: English
• Subjects: Applied sciences; Corrosion; Corrosion environments; Exact sciences and technology; Metals. Metallurgy
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/0010-938X(95)00048-O

The formation of a single amorphous Fe-Cr-P phase was strongly related to the amount of phosphorus addition. The structure of the melt-spun Fe-8Cr-P alloys containing 16.5 at% or more phosphorus was confirmed to be amorphous by X-ray diffraction (XRD). However, high-resolution transmission electron microscopy (TEM) revealed that a microcrystalline bcc Fe phase was dispersed in the amorphous matrix of the Fe-8Cr-16.5P and Fe-8Cr-18P alloys. The corrosion behavior of Fe-Cr-P alloys is significantly sensitive to the presence of microcrystallites in the amorphous matrix. A thick corroded layer was formed on the Fe-8Cr-16.5P and Fe-8Cr-18P alloys by immersion in 9M H 2SO 4. A TEM image for the thick corroded layer of the Fe-8Cr-16.5P alloy showed that the microcrystalline bcc Fe phase was preferentially dissolved away in the solution and that the amorphous Fe-Cr-P phase remained on the surface of the alloy without dissolution. Accordingly, the thick corroded layer corresponds to the amorphous Fe-Cr-P phase which is covered with the passive film. The addition of 20 at% phosphorus is necessary to form an almost complete amorphous structure and to provide the high corrosion resistance even in 9M H 2SO 4.