Solidification processing, mechanical properties and oxidation of ruthenium aluminide-based alloys

Alloys within the Ru-Al-Mo and Ru-Al-Cr systems were investigated to find possible candidates for high temperature structural applications based on ruthenium aluminide (RuAl). Alloys of RuAl-Ru(Mo) had fracture toughness values that ranged from 13 to 37 MPa√m, but had poor oxidation resistance at 1100 °C. Substituting Cr for Mo improved oxidation resistance. The fracture toughness of a RuAl-Ru(Cr) alloy was 38 MPa√m while a single phase Ru(Cr,Al) was found to be 68 MPa√m As the volume fraction of RuAl increased, the fracture toughness decreased.; Upon heat treatment at 1100 °C, a single phase Ru(Cr,Al) alloy formed RuAl precipitates. The fracture toughness did not change from the formation of precipitates, but room temperature yield strength increased from 535 to 1060 MPa and tensile elongation dropped from 13% to <1%. The RuAl precipitates were found to embrittle the grain boundaries resulting in poor ductility. The single phase Ru(Cr,Al) alloy was found to have the best combination of mechanical properties and oxidation resistance of the alloys investigated.