The Effect of Ramp Heating on the Microstructure and Surface Chemistry of APMT FeCrAl Alloy

The APMT FeCrAl alloy is a cladding candidate for the accident-tolerant fuel (ATF) systems in light water reactors (LWRs) due to its ability to form a protective Al2O3 film on the surface at temperatures greater than 1000 °C. In order to understand the alumina evolution at the early stages of high-temperature exposure in short periods, an APMT tube specimen was heated up rapidly to melting temperature in a flowing 100 % water and steam environment. Using transmission electron microscopy (TEM), the presence of a ∼ 90 nm thick oxide layer was confirmed. The surface chemistry of APMT was characterized layer by layer using X-ray photoelectron spectroscopy (XPS) depth profiling. The results indicated a thin layer composed of oxides and hydroxides of Al, Cr, and Fe with varying proportions at different depths in the oxide layer. The microstructure of the oxide layer was characterized using X-ray diffraction and showed the presence of α-Al2O3 and γ-Fe2O3/Fe3O4 after ramp heating. The results depict the ability of the APMT FeCrAl alloy to form a protective oxide layer in less than a second on exposure to steam under high ramp rates.