Abstract
The oxidation behavior of Fe–20Cr–4Al alloys containing 0.01, 0.04 and 0.37%Ce was studied in air at temperatures between 1273 and 1523 K by weight-change measurements, X-ray diffraction, electron probe microanalysis and scanning electron microscopy. The surface oxide predominantly formed on all the alloys was α-Al2O3. The marker and kinetic studies suggested that the α-Al2O3 scale grew into the alloy substrate by the inward diffusion of oxygen along the oxide grain boundaries. In the alloys without Ce and with 0.01%Ce, the α-Al2O3 scale spalled during cooling from the oxidation temperature. Spalling of the surface oxide, probably caused by the void formation at the oxide/alloy interface, initially occurred at the intersection of the grain boundaries and subsequently extended to the interior of the grains. No spalling was observed on the surface of the alloys with 0.04 and 0.37%Ce. In both alloys cerium primarily existed all over the matrix as a Ce–Fe intermetallic compound, which mostly precipitated at the grain boundaries. Higher cerium additions resulted in good adherence of the surface oxide due to the prevention of the void formation at the oxide/alloy interface, and pegging effect of intergranular oxide preferentially formed at the grain boundaries.
