Oxidation behavior of Ru(Al)–RuAl intermetallic eutectics produced by ingot and powder metallurgy

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

“…7. This is in accordance to the observations in literature [11,17,18], although in those investigations the total thickness of the Al 2 O 3 scale was greater than in the present work.…”

“…The data seems to fit a linear time dependence, which agrees with the transport mechanisms that could be acting in an open oxide structure [20]. The estimated constant of the linear growth rate (k L w1.75 mm/h-at 1000 8C) is somewhat smaller than that for pure eutectic samples studied under similar conditions (k L w2.73 mm-at 1100 8C) [18]. However, some uncertainties remain due to the considerable data scatter.…”

“…2, 3 and 7) was already observed in near stoichiometric RuAl oxidized above 1200 8C [11,17], in a eutectic RuAl alloy oxidized at 1100 8C [18], and in IrAl oxidized at 1300 and 1600 8C [19]. Examination of the compositions of the scales by microprobe mapping [11] and X-ray elemental mapping [17,18] indicated that the bands near the alloy/scale interface were composed alternately of alumina layers and ruthenium oxide. This is in accordance with the compositions measured with EDS (on Table 1).…”

Oxidation of ruthenium aluminide-based alloys: The role of microstructure and platinum additions

“…8) are composed of alternating layers of Al 2 O 3 and Ru-rich phases next to the outer Al 2 O 3 layer after cyclic oxidation at 1100 C. The outer Al 2 O 3 layer appears to be fragile and porous and thus unprotective. The formation of the alternating multilayer structure beneath the Al 2 O 3 scale was observed in near-stoichiometric RuAl isothermally oxidized at 1350 C [4], in a eutectic RuAl alloy [33], and in near-stoichiometric RuAl alloys [13,15] oxidized between 1000 C and 1300 C. A similar alternating multilayered structure has been observed in the IrAl and Ir x Ru 1ÿx Al systems with alternating layers of Al 2 O 3 and Ir-rich or Ir/Ru-rich phases during isothermal oxidation at temperatures up to 1400 C [32,34]. The formation of the layered structure has been attributed to the slower nucleation and growth kinetics of the Al 2 O 3 at the reaction front compared to the inward diffusion rate of oxygen [34].…”

RuAl and its alloys, Part II: Mechanical properties, environmental resistance and applications

“…This is characterized by, on one hand, columnar grains next to the RuAl substrate, and on the other hand, equiaxed and needle-like morphology at the surface. As oxidation time increases, the periodic structure propagates inwards and consumes the bulk material, leaving Al 2 O 3 on the free surface of the sample [11,46,86,87,97,98]. It was also reported that whiskers of Al 2 O 3 form on the free surface of the oxidized single-phase or near single-phase alloy samples [91,92,95], whereas the oxide layer on the Ru(Al)eRuAl eutectic alloy has a nodular morphology [97].…”