Secondary corrosion protection of FeCr(Al) model alloys at 600 °C – The influence of Cr and Al after breakaway corrosion

J Eklund,A Persdotter,I Hanif,S Bigdeli,T Jonsson

doi:10.1016/j.corsci.2021.109584

Abstract

The influence of Cr and Al content on the oxidation behaviour of FeCr(Al) model alloys after breakaway oxidation at 600 °C and the underlying mechanisms were investigated in detail with thermogravimetrical analysis (TGA), thermodynamic calculations and advanced electron microscopy. The results showed that a Cr-content of ≥18 wt% drastically reduced the growth rate of the Fe-rich oxide scale, formed after breakaway oxidation, for FeCrAl alloys but not for FeCr alloys. This was attributed to the ability of the Fe(18-25)CrAl alloys to prevent internal oxidation, which enables the formation of a healing layer.

Highlights

High temperature corrosion is an issue present in many applications, which often negatively impacts the efficiency of the involved processes and generally increases the maintenance costs due to accelerated ma terial degradation
A possible solution to prevent breakaway oxidation is to use aluminaforming alloys, i.e. FeAl or FeCrAl alloys, with the ability to form Al-rich M2O3 oxide scales at elevated temperatures
Exposure in the presence of K2CO3 resulted in rapid breakaway oxidation for all alloys, i.e transition from the primary to the secondary corrosion regime

Summary

Introduction

High temperature corrosion is an issue present in many applications, which often negatively impacts the efficiency of the involved processes and generally increases the maintenance costs due to accelerated ma terial degradation. In the presence of these compounds the (Cr, Fe)2O3 oxide scale may be depleted in Cr through two separate mechanisms: In the presence of alkali compounds, Cr depletion takes place due to the formation of alkali chromates [1,2,3]; In the presence of water vapour, Cr depletion is caused by evaporation of chromium oxy hydroxide (CrO2(OH)2) [4,5,6,7] Both of these mechanisms eventually cause the protective (Cr, Fe)2O3 oxide to break down, which is followed by the formation of a faster growing multi-layered Fe-rich oxide scale. This phenomenon is generally referred to as breakaway oxidation. A different approach was recently investigated by Persdotter et al [24] in which two different corrosion regimes were distinguished: Primary (Cr- and/or Al-rich M2O3 oxide scale(s)) and Secondary (multi-layered Fe-rich oxide scales)

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