Simultaneous improvement in fracture toughness and oxidation resistance of Nb-Si based alloys by vanadium addition

The microstructural characterization, fracture toughness and oxidation resistance of Nb-15Si-24Ti-4Cr-2Al-2Hf (at%, V-free) alloys and Nb-15Si-24Ti-4Cr-2Al-2Hf-1V (at%, 1V) alloys were investigated. Results showed that the V-free alloys and 1V alloys both consisted of Nbss, αNb5Si3 and γNb5Si3 phases, and V was primarily partitioned in Nbss phases. Compared with the V-free alloys, the 1V alloys were featured by a better continuity of Nbss, finer average diameter of silicides and lower volume fraction of γNb5Si3. The 1 at% addition of V enhanced the fracture toughness of Nb-Si based alloys from 9.87 to 12.98 MPa m1/2 at room temperature. The fracture surfaces of 1V alloys were more undulated, compared with those of the V-free alloys. The 1 at% addition of V significantly improved the oxidation resistance of Nb-Si based alloys, by reducing the weight gain from 264.7 to 148.5 mg/cm2 after oxidation at 1300 °C for 100 h. The transition from a paralinear oxidation kinetic to a parabolic oxidation kinetic was triggered by the addition of V.