High temperature strength, fracture toughness and oxidation resistance of Nb–Si–Al–Ti multiphase alloys

Nb?Si?Al?Ti quaternary phase diagram around three-phase region, which consists of niobium solid solution (Nbss), Nb3Al and Nb5Si3, is constructed in this study. The three-phase region exists up to titanium content of about 20?mol%. Based on the quaternary phase diagram, three-phase alloys containing Nbss from about 50 to 75% in volume are prepared to improve high temperature strength, room temperature fracture toughness and oxidation resistance simultaneously.When microstructure and composition are optimized (Nbss+Nb3Al+Nb5Si3) three-phase alloy with the addition of titanium exhibits higher compressive strength than nickel-based superalloys at room temperature to 1573?K. Fracture toughness at room temperature of (Nbss+Nb3Al+Nb5Si3) three-phase alloys is increased to over 12?MPa?m1/2 by the addition of titanium without sacrificing high temperature strength. Oxidation resistance of (Nbss+Nb3Al+Nb5Si3) three-phase alloys is improved by the addition of titanium.