Effects of TaB2 addition on microstructure and mechanical properties of Nb[sbnd]Si based alloys

Abstract

The effects of TaB2 addition on the Nb-16Si-22Ti-3Al alloy were investigated in this study. The results showed that the Nb-16Si-22Ti-3Al alloy consisted of the Nbss phase, α-Nb5Si3 phase, Nb3Si phase, and Tiss phase. With the addition of TaB2 increased from 0 to 0.25 at. %, the Nb3Si disappeared and the eutectic transformation reaction occurred (Nb3Si → Nbss + α-Nb5Si3), which made the volume fraction of the Nbss phase increased from 38.6% to 50.3%. With the TaB2 addition further increasing to 2.0 at. %, the α-Nb5Si3 became the primary phase, and the microstructure transformed from the Nbss + α-Nb5Si3 eutectic structure to the primary α-Nb5Si3 and (Nbss + γ-Nb5Si3) hypereutectic structure. The alloy with 0.25 at. % TaB2 addition had the highest fracture toughness of 10.2 MPa•m1/2 due to the refinement of microstructure and the increment of ductile Nbss. The maximum compressive strength of TaB2 added alloy at room temperature reached 2587.25 MPa in 2.0TaB2 specimen, owing to the solid solution strengthening of Ta and B, and the increment of the silicides content. Additionally, by comparing the fracture toughness of alloys with TaB2 addition obtained by three-point bending (SENBs) and indentation methods, respectively, the feasibility of estimating the fracture toughness of NbSi based alloys by the indentation method is demonstrated with an error of below 20%, which provided a basis for subsequent rapid performance characterization.