Element redistribution in the oxide scale during air oxidation of Kanthal AF alloy

Karpe, Blaž (author), Kovač, Janez (author), Manfreda, Monika (author), Bizjak, Milan (author), Veskovič Bukudur, Stojana (author), Cerc Korošec, Romana (author), Umek, Polona (author)

The oxidation mechanism of Kanthal AF (FeCrAl alloy) was studied in the temperature range of 800–1200 °C through isothermal and thermo-cyclic oxidation tests. At 800 °C, tests involved 12-hour cycles (up to 36 cycles), while at 1000 °C and 1200 °C, they were conducted isothermally (up to 432 hours). Oxidation constants, oxide scale thickness, surface microstructure, and elemental composition were analyzed using TGA, SEM-EDXS, TEM, AES, XPS, GIXRD, and ToF-SIMS. The results show that the Al$_2$O$_3$ layer has a multilayer structure, defined by a naturally formed thin Cr-rich oxide layer on the alloy surface, which exhibits temperature-dependent selective permeability of metal cations, influencing the oxide scale growth. At 800 °C, inward oxide diffusion dominates due to limited cation permeability in the Cr-rich layer, while at higher temperatures, outward growth of the alumina scale is facilitated by increased permeability to metal cations. Despite the low Mg concentration in the alloy (0.01 wt.%), Mg diffuses into the alumina rapidly, forming Mg-Al-Fe oxides that transform into MgAl$_2$O$_4$ spinel, impacting scale integrity and adhesion due to associated porosity. Consequently, Mg is considered an undesirable impurity, even at trace levels. Titanium forms separate oxides in the alumina scale, while zirconium and yttrium incorporate uniformly into the alumina scale.

• Language: English
• Keywords: Kanthal alloys, oxidation tests, protective alumina scale, high temperature oxidation, FeCrAl alloys, element distribution in alumina scale
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: NTF - Faculty of Natural Sciences and Engineering; FKKT - Faculty of Chemistry and Chemical Technology
• Publication status: Published
• Publication version: Version of Record
• Year: 2024
• Number of pages: Str. 8720-8729
• Numbering: Vol. 33
• PID: 20.500.12556/RUL-169759
• UDC: 620.1/.2
• ISSN on article: 2214-0697
• DOI: 10.1016/j.jmrt.2024.11.169
• COBISS.SI-ID: 216298243
• Publication date in RUL: 09.06.2025

Record is a part of a journal

• Title: Journal of materials research and technology
• Publisher: Brazilian Metallurgical Materials and Mining Association, Elsevier
• ISSN: 2214-0697
• COBISS.SI-ID: 56382211

Licences

• License: CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
• Link: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Description: The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.

Secondary language

• Language: Slovenian
• Keywords: zlitine FeCrAl, zlitine, jeklo, oksidacija