Effect of Water Vapor on the Oxidation Behavior of the Eutectic High‐Temperature Alloy Mo‐20Si‐52.8Ti

Matthias Weber,Hans-Jürgen Christ,Susanne Obert,Martin Heilmaier,Bronislava Gorr,Alexander Kauffmann

doi:10.1002/adem.202000219

Matthias Weber, Hans-Jürgen Christ + Show 4 more

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https://doi.org/10.1002/adem.202000219

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Abstract

Herein, the effect of water vapor on the oxidation resistance of the alloy Mo‐20Si‐52.8Ti (at%) is investigated. The alloy is oxidized in dry, wet, as well as in in situ changing atmospheres at 1100 °C. The oxidation kinetics changes from nearly parabolic to linear if water vapor is present in oxidizing atmosphere. Under all conditions, the oxide scales consist of an outer TiO2 and a TiO2SiO2 duplex layer underneath. In wet atmosphere, the thicknesses of the two regions substantially increase indicating a severe ingress of water vapor. The inferior oxidation resistance in wet environment is primarily rationalized by the fast diffusion of H2O through SiO2.

Highlights

Introduction behavior ofMoSi2 in dry air, wet air, and pure oxygen between 400 and 600 C.[16]
The eutectic alloy Mo-20Si-52.8Ti consists of two phases, a bright body-centered cubic solid solution (Mo,Si,Ti) and a (Ti,Mo)5Si3 phase (Strukturbericht D88), which appears dark in the backscatter electron (BSE) mode
Accelerated linear kinetic was observed during oxidation in wet atmosphere indicating more severe oxygen and presumably H3Oþ and OHÀ ingress

Summary

Introduction

Introduction behavior ofMoSi2 in dry air, wet air, and pure oxygen between 400 and 600 C.[16]. The effect of water vapor on the oxidation oxidation resistance is a well-known shortcoming that restricts behavior of multiphase Mo─Si─B alloys was studied by their industrial application so far.[4,5] Recently, outstanding oxida- Mandal et al.[18] the initial mass loss due to the evapotion resistance in air was detected for some multiphase Mo─Si─Ti alloys at 1100 and 1200 C.[6,7] Surprisingly, the ubiquitous pesting phenomenon at 800 C could be reliably suppressed.[8,9,10] The ration of MoO3 was approximately independent on the moisture content of the atmosphere, accelerated growth of the glassy scale as well as the MoO2 layer underneath was identified. At Ti contents of 43 at% and above, absence of of water vapor on the oxidation behavior of ternary Mo─Si─Ti catastrophic oxidation at 800 C is observed even though TiO2 is the major phase within the duplex scale.[7]

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