Long-term corrosion behavior of FeCr(Al, Ni) alloys in O2 + H2O with KCl(s) at 600 °C: Microstructural evolution after breakaway oxidation

Abstract

The microstructural evolution of the oxide scales formed on FeCr(Al,Ni) alloys after breakaway oxidation was studied in 5 % O2 + 20 % H2O + N2 (Bal) + KCl(s)/KCl(g) at 600 °C for 168, 1000 and 8000 h. The SEM/EDS, SEM/EBSD and XRD investigation show that all alloys experience breakaway oxidation and form multi-layered scales. Experimental results, thermodynamic modelling and kinetic simulations show that FeCrAl and FeCrNi alloys form chromium-rich spinel oxide in inward-growing scales which transform into a protective corundum-type oxide as the oxidation progresses, while FeCr alloy experiences fast oxidation and maintains a non-protective spinel oxide/internal oxidation after long exposures.