Investigation on the composite effect of Zr and Cr on oxidation behavior and fracture toughness of Nb-Ti-Si-based alloys manufactured by directed energy deposition

Nb-Ti-Si-based in-situ composites are expected to be very promising materials for high-temperature structures seen in cutting-edge engines. However, the subpar fracture toughness and poor oxidation resistance severely limit their engineering application. To customize the microstructure and performance of directed energy deposition (DED) Nb-Ti-Si-based in-situ composite, it is important to comprehend the impact of alloying element. The present study examines the composite effect of Zr and Cr on room-temperature fracture toughness and high-temperature (1250 °C) oxidation behavior of Nb-23Ti-14Si-based in-situ composites produced by DED. With the co-alloying of Zr and Cr, (γ, α)-Nb₅Si₃ and Cr₂Nb phases are formed in the DED-built Nb-23Ti-14Si-xZr-yCr (x = 3-6 at.%Zr, y = 5-10 at.%) alloys. The formation mechanisms of the oxide scales on Nb-23Ti-14Si-based alloys during the oxidation process have been discussed. With the co-alloying of 6 at.%Zr + 12 at.%Cr, it presents the best oxidation resistance, and the weight gain at 1250 °C for 20 h has decreased to 34.67 mg/cm². An enhancement in fracture toughness (K_Q) to 14.46 MPa·m^1/2 was achieved by alloying with 6 at.%Zr + 5 at.%Cr.