Zr addition-induced transitions of deformation mechanism at high temperatures of Nb-Si-Ti based multi-alloys: Super-dislocations in γ-Nb₅Si₃

In this work, mechanisms of two different deformation and fracture modes at 1250 °C of directional solidified Nb-Si-Ti based multi-alloys are investigated to explore the influence of element Zr on the high temperature properties. The 5Zr alloy exhibits the least drop of tensile strength and it shows the best comprehensive property of the plasticity and the tensile strength. Zr reduces α-Nb₅Si₃ and weakens the load-carrying capacity at high temperatures. Meanwhile, γ-Nb₅Si₃ are introduced by the addition of Zr which improve the plasticity and provides a significant work hardening to recover the tensile strength at 1250 °C. New super-dislocations are discovered for the first time with a slip system of <11¯01>(112¯0) in γ-Nb₅Si₃ which significantly improve the plasticity and promotes a coordinated deformation between Nb solid solutions and γ-Nb₅Si₃. Due to the different phase compositions, two models are derived to discuss the deformation mechanisms at high temperatures. In order to achieve an enough tensile strength at high temperatures, it is suggested that microstructures consisting of two phases is more beneficial to provide a good load-carrying capacity (Nbss/α) or a significant work hardening (Nbss/γ) at high temperatures.