Combined effect of NdNbTiO₆ precipitation and fine microstructure on oxidation resistance of Nb-Si alloys at 1250 °C

• Fracture toughness was increased to 17.5 MPa·m1/2 by addition of 0.4% Nd. • The alloy with 0.4 at. % Nd addition exhibits the most superior oxidation resistance at 1250°C. • Nd mainly exists as Nd2O3 in the alloys, which occurs N d 2 O 3 + 2 Ti O 2 + N b 2 O 5 → 2 NdNbTi O 6 during the oxidation. • Nd enhances the oxidation resistance of the alloy by forming NdNbTiO6 and refining microstructure. The oxidation behavior and resistance of Nd-doped Nb-Si-based alloys at 1250°C were studied. At a Nd content of 0.4%, the K Q value reached 17.5 MPa m 1/2 . Microcracks develop within near-eutectic clusters, serving to impede the propagation of the main crack and thereby boost fracture toughness. Oxidation tests show that the 0.4 at.% Nd alloy demonstrates optimal oxidation resistance, with a mass gain of 128.1 mg/cm² after 50 h at 1250°C—45.3% lower than the 0.05 at.% Nd alloy (234.2 mg/cm²). During oxidation, Nd₂O₃ reacts with Nb₂O₅ and TiO₂ to form NdNbTiO₆, which pins at phase boundaries and hinders inward oxygen diffusion. Additionally, a refined microstructure decreases oxidation rate and improves scale density. Therefore, the appropriate addition of 0.4 at.% Nd enhances the oxidation resistance of Nb-Si-based alloys primarily due to the synergistic effects of: (1) the formation of interfacially-pinned NdNbTiO₆ particles that impede grain boundary migration; and (2) the continuous and dense NdNbTiO₆ layer that serves as a diffusion barrier to inward oxygen transport.