Effect of Fe and partial pressure of oxygen on the formation and phase transformation behavior of Al 2 O 3 scale

The effect of oxygen partial pressure on the phase transformation of Al 2 O 3 scale on various Fe–Al alloys with and without very thin (∼100 nm) Fe coating was investigated. Fe‐coating on Fe–Al alloys can effectively suppress metastable Al 2 O 3 formation, but little effect was observed when the samples were oxidized in a low partial pressure of oxygen. Under the low ${\rm P}_{{\rm O}_{{\rm 2}} } $ atmosphere, metastable to stable α‐Al 2 O 3 scale phase transformation on both Fe‐coated and non‐coated Fe–Al alloys was significantly delayed. The lattice spacing of α‐Al 2 O 3 scale formed in air decreased with increasing alloy Al content. Further decrease in the lattice spacing of α‐Al 2 O 3 scale was observed when the alloy was oxidized in low ${\rm P}_{{\rm O}_{{\rm 2}} } $ . The results obtained clearly indicated that the formation of Fe 2 O 3 or Fe 3+ in metastable Al 2 O 3 accelerated the metastable to stable α‐Al 2 O 3 scale transformation.