Effect of Y-La Addition on Interfacial Reaction and Cyclic Oxidation Behavior of Nickel-based Single Crystal Superalloy

Abstract

Y-La was added into the second generation of nickel base single crystal superalloy and two kinds of alloy castings with Y-La content of 5.26 × 10–4%(mass fraction, ) Y + 6.05 × 10–4% La and 47.64 × 10–4% Y + 69.09 × 10–4% La were obtained after directional solidification. The effect of Y-La content on the interface reaction between alloy melts and Al2O3 based ceramics during directional solidification was investigated. The effect of alloy content on oxidation resistance of alloy at 1100 oC under cyclic oxidation was studied. The microstructure at the interface between alloy and mould, as well as the surface cross-section and fracture morphologies of the specimens, was characterized by means of scanning electron microscope (SME) with an energy-dispersive spectroscopy attachment. The phases of the oxides were identified by X-ray diffraction. The results show that the increase of Y-La content promotes the interfacial reaction, which makes the reaction layer thicker and more complex. The main reaction products are oxides containing Y and La. The addition of Y-La obviously improves the oxidation resistance of the alloy and reduces the exfoliation of the oxide film on the surface of the alloy. However, excessive Y-La will deteriorate the oxidation resistance of the alloy, accelerate the oxidation weight gain rate of the alloy. And the oxide film of the alloy surface has obvious traces of exfoliation, more holes and serious internal oxidation.

Keywords

• rare earth elements
• Ni-based superalloys
• interfacial reaction
• cyclic oxidation