High-temperature oxidation behaviour of Zr alloyed Fe3Al-type iron aluminide

The oxidation behaviour of two Fe3Al-based Fe–Al–Cr–Zr–C alloys has been evaluated between 900 and 1200 °C. The alloys contained either (Fe,Al)2Zr Laves phase or ZrC carbide. The alloys were oxidised for up to 1000 h in synthetic air using thermogravimetric analysis (TGA). Scales that formed on the surfaces of the sample as well as cross sections were analysed by light optical microscopy (LOM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectrometry (EDS).At 900 °C parabolic growth and low weight gains for both tested alloys were observed. The scales are predominantly formed by Al2O3 with minor amounts of ZrO2. Some Fe2O3 was observed after oxidation at 900 °C. At 1000 °C oxidation ingresses into the samples along grain boundaries due to preferential oxidation of the Zr-rich precipitates, becoming more severe at higher temperatures. Ingress of oxidation into the sample is more pronounced for the alloy containing ZrC where at 1200 °C it is not any longer limited to the carbide but extends markedly into the Fe3Al matrix.

► The two Fe–Al–Cr–Zr–C alloys were oxidised at high temperatures (900–1200 °C).
► Both alloys have very good oxidation resistance at 900 °C.
► Above 1000 °C both alloys showed ingress of oxidation.
► Oxide protrusions are caused by preferential oxidation of Zr-rich precipitates.
► ZrC precipitates is oxidised more readily than the (Fe,Al)2Zr Laves phase.