Decomposition of Nb₃Si and mechanical-property improvement by adding appropriate amount of MgO in Nb–16Si–20Ti alloy

Five Nb–16Si–20Ti–xMgO alloys (x = 0, 0.1, 0.5, 1.0 and 3.0) were prepared via arc melting in this study, and the effect of MgO addition on their phase composition, microstructure evolution, and mechanical properties was examined. The results demonstrated that MgO reacted with the Nb–Si–Ti alloy while Mg atoms replaced Nb atoms in the Nbss phase. The hypoeutectic alloy was transformed into a hypereutectic alloy upon the addition of 3.0 at% MgO, and the Nb₃Si phases decomposed into a fine Nbss/α-Nb₅Si₃ eutectic structure. The highest fracture toughness was achieved for the Nb–16Si–20Ti–3MgO alloy, with an ambient fracture toughness value of 9.4 MPa·m^–1/2 due to its largest Nbss phase content and optimal Nbss/α-Nb₅Si₃ eutectic structure. Furthermore, the alloy compressive strength increased with MgO addition. The compressive strength of the Nb–16Si–20Ti–3MgO alloy was 2624.1 MPa, 26.0% higher than that of Nb–16Si–20Ti, due to the formation of a solid solution of Mg atoms in the Nbss phase and reinforcement of a small amount of the Ti₂O phase. Finally, an increase in the content of the Nbss/α-Nb₅Si₃ eutectic structure increased both the alloy strength and fracture strain. Graphical abstract: [Figure not available: see fulltext.].