Microstructural and chemical constitution of the oxide scale formed on a pesting-resistant Mo-Si-Ti alloy. (January 2021)

• Record Type: Journal Article
• Authors: Obert, Susanne; Kauffmann, Alexander; Seils, Sascha; Boll, Torben; Kauffmann-Weiss, Sandra; Chen, Hans; Anton, Ronja; Heilmaier, Martin
• Is Part Of: Corrosion science. Volume 178(2021)
• Publication Date: 2021-01
• Subjects: Refractory alloys -- Oxide scale -- Microstructure -- Chemical composition -- Crystal structure -- Oxidation kinetics; Corrosion and anti-corrosives -- Periodicals; 620.11223
• DOI: 10.1016/j.corsci.2020.109081
• Languages: English
• ISSNs: 0010-938X

Abstract

Highlights: The oxidation behaviour of pesting-resistant Mo-20Si-52.8Ti was investigated. The scale forms slowly at 800 °C: cubic kinetics following linear kinetics. It is composed of a Ti(+IV)-oxide and SiO2 islands. The scale comprises strongly off-stoichiometric Ti- and Si-oxide at 1200 °C. Here, diffusion-controlled parabolic kinetics prevail. Abstract: The oxidation behaviour of the pesting-resistant eutectic alloy Mo-20Si-52.8Ti was investigated by addressing the microstructural and chemical constitution by grazing incidence X-ray diffraction GIXRD and atom probe tomography APT of oxide scales formed at 800 and 1200 °C in order to understand their protective character. The duplex Si-Ti-oxide scale formed at 800 °C in air, i.e. within the so-called " pesting regime ", is considerably slow growing with a scale thickness of (11 ± 3) μm after 1000 h of exposure. It is composed of a Ti(+IV)-oxide with the chemical composition of approximately TiO2.1 confirmed by APT and SiO2 islands, which are most likely amorphous. The oxide scale formed at 1200 °C, a potential application temperature, is characterised by a top single-phase scale and an underlying duplex scale with a considerably increased thickness of (68 ± 11) μm in total. It consists of rutile TiO2 and some cristobalite SiO2 as determined by GIXRD. APT analysis of the top Ti-oxide scale confirms the stoichiometry TiO2.2 . The underlying duplex scale comprising Ti- and Si-oxide is characterised by strongly off-stoichiometric compounds, namely TiO1.4 and SiO1.6 . Initial linear oxide scale growth kinetics are found at 800 °C, which change to cubic kinetics for exposure times longer than 100 h. At higher temperatures of 1100 and 1200 °C, diffusion-controlled, almost parabolic kinetics prevail.