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.