Abstract:Nb-Si based alloys show great promise to surpass current advanced Ni-base superalloys due to their low densities and high melting points. Both Ti and Al are beneficial alloying elements for Nb-Si based alloys. In the literature, small amount (≤ 3 at. % ) of Al have frequently examined, and Nb aluminides are usually not formed in this case. Since Nb3Al and Nb2Al have good strength and creep properties, NbAl3 is also a candidate hot-section material, and the study of Nb-Si alloys with these possible Nb alumininides is lacking, so we focus our efforts on primarily whether Nb aluminide is formed or not by adding more Al in the as-cast Nb-Ti-Si alloys. This work studied the microstructures and mechanical properties of two Nb-Ti-Si-Al alloys (A2: Nb-18Ti-14Si-9Al, A4: Nb-21Ti-14Si-9Al) with higher Al content, and the A4 alloy was designed to examine the alloying effect of more Ti. The A2 alloy consists of (Nb), Nb5Si3 and Nb3Al, while the A4 alloy is composed of (Nb) and Nb5Si3. The comparable fracture toughness of the A2 alloy and the A4 alloy is 11.1 MPa.m1/2 and 10.9 MPa.m1/2, respectively. Moreover, the indention experiments are employed to characterize the micro scale mechanical properties of these Nb-Ti-Si-Al alloys.