Oxidation behavior of a Mo (Si, Al) 2-based composite at 300–1000 °C

Abstract

The oxidation behavior of a Mo (Si,Al) 2-based composite of Mo(Si,Al) 2, Al 2O 3 and Mo 5(Si,Al) 3 (Kanthal Super ER) in synthetic air was investigated. The samples were oxidized isothermally for up to 72 h at 300–1000 °C using a thermobalance. The microstructure was analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) depth profiling. Broad ion beam milling (BIB) was used to prepare cross-sections. Oxidation behavior depended strongly on the composition of the substrate which consisted of a Mo(Si,Al) 2 matrix and the minority phases Mo 5(Si,Al) 3 and Al 2O 3. At 300–500 °C the mass gains were small with parabolic kinetics, oxidation resulting in a mixture of oxides that reflects the substrate composition. At 600 and 700 °C the oxide scale is thin and protective and depleted in molybdenum, a mass loss occurring due to MoO 3 vaporization. At 1000 °C a protective α-alumina scale forms.