Cyclic oxidation of Ru-containing single crystal superalloys at 1100 °C

The cyclic oxidation behavior of Ru-containing single crystal superalloys at 1100 °C has been investigated in alloys with Ru contents ranging from 3.5 to 9 at.% (5.7–14.1 wt.%) and Cr additions ranging from 0 to 8 at.% (0–6.7 wt.%). High levels of Cr additions (8 at.%) significantly improved oxidation resistance, while increased levels of Ru adversely affected the oxidation performance. A multi-layered scale formed on the alloy surface, and it generally consisted of an external layer of NiO, an intermediate layer of spinel and an Al2O3 inner layer. The presence of a continuous α-Al2O3 inner layer clearly improved oxidation performance. Ru-rich precipitates were observed in the spinel layer of alloys which displayed poor oxidation resistance. High levels of Cr additions not only reduced the propensity for formation of Ru-rich phases in the oxide, but also promoted the formation of a continuous alumina layer adjacent to the superalloy, without stabilization of any detrimental phases in the superalloy.