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

Abstract

Nb–Si–Al–Ti quaternary phase diagram around three-phase region, which consists of niobium solid solution (Nb_ss), 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 Nb_ss 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 (Nb_ss+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 (Nb_ss+Nb₃Al+Nb₅Si₃) three-phase alloys is increased to over 12 MPa m^1/2 by the addition of titanium without sacrificing high temperature strength. Oxidation resistance of (Nb_ss+Nb₃Al+Nb₅Si₃) three-phase alloys is improved by the addition of titanium.