Investigating Scandium-Alloyed Nb-Si Systems: Microstructure, Oxidation Behavior, and Fracture Toughness

Abstract

In order to synchronize the oxidation resistance and room temperature fracture toughness of Nb-Si based alloys to meet the development needs, the effects of Sc addition on microstructure evolution, oxidation resistance and mechanical performance of Nb-16Si-20Ti-1.5Zr-1C-1B-xSc (x = 0, 0.1, 0.3, 0.5, 0.8) alloys are studied systematically. All compositions of the alloys are composed of two phases, Nbss and γ-(Nb,X)5Si3, X-ray diffraction and electron microscopy reveal that Sc addition refines γ-(Nb,X)5Si3 phases and promotes a transition from primary to lamellar eutectic structures, enhancing oxidation resistance. Sc2O3 formation at phase boundaries impedes oxygen diffusion, forming continuous oxide barriers (TiO2 and SiO2), thereby improving oxidation resistance. Mechanical testing shows an increase in fracture toughness with Sc doping, attributed to enhanced crack deflection and energy absorption within the Nbss phase. These results are important for the simultaneous improvement of room-temperature fracture toughness and high-temperature oxidation resistance as well as the mechanism of action of the rare earth element Sc, and for the further development of Nb-Si based superalloys to meet practical needs.

Keywords: Keywords: Nb-Si based alloy, Sc2O3, Oxidation, Fracture toughness