Influence of the microstructure on the formation of alumina scales on near stoichiometric RuAl produced by arc melting

The influence of the microstructure on the oxidation behavior of two-phase near stoichiometric RuAl produced by arc melting was investigated. The oxidation was conducted at 1000 °C. The oxide scale growth and phase formation were studied using scanning electron microscopy, focused ion beam microscopy and in situ X-ray diffraction. The microstructure of the samples consisted of RuAl grains with continuous or isolated intergranular phase composed of Ru(Al) or Ru(Al)-RuAl eutectic. The Ru(Al) intergranular layer is prone to oxidation, which was not observed in samples with intergranular Ru(Al)-RuAl eutectic. Porous, poor-protective α-Al2O3 scales were formed. A region with periodic Aluminum oxide/Ruthenium oxide banded layers was developed beneath the external α-Al2O3 scale. Scale growth follows a linear rate law.